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Master the chemistry of carbon compounds—from nomenclature and reaction mechanisms to polymers and materials—with systematic problem-solving strategies for organic synthesis.
IUPAC nomenclature provides a systematic way to name organic compounds. For HSC Chemistry, you must be able to name compounds from C1 to C8 and apply functional group priority rules.
The parent chain (longest continuous carbon chain) determines the stem name:
| Carbons | Prefix | Alkane |
|---|---|---|
| 1 | meth- | methane |
| 2 | eth- | ethane |
| 3 | prop- | propane |
| 4 | but- | butane |
| 5 | pent- | pentane |
| 6 | hex- | hexane |
| 7 | hept- | heptane |
| 8 | oct- | octane |
Memory tip: "My Elephant Plays Piano, But Prefers Heavy Orchestra" (Meth, Eth, Prop, Pent, But, Hex, Hept, Oct - note But and Pent reversed in the mnemonic to help remember the spelling)
When multiple functional groups are present, the highest priority group determines the suffix. Lower priority groups become prefixes.
Priority order (highest to lowest):
Example: If a molecule contains both -OH and C=C, the alcohol takes priority for the suffix (-ol), and the alkene is indicated by inserting "en" before the -ol: hex-2-en-1-ol
Step 1: Find the longest carbon chain containing the highest priority functional group. This is the parent chain.
Step 2: Number the chain from the end that gives the lowest number to the highest priority functional group (or to the first point of difference if groups have equal priority).
Step 3: Name substituents with their position numbers. List alphabetically (ignoring di-, tri-, etc.).
Step 4: Assemble the name:
[position]-[substituent(s)]-[parent stem]-[position]-[suffix]
Important rules:
Examples:
CH₃CH₂CH₂CH₃ = butane
CH₃CH(CH₃)CH₃ = 2-methylpropane
CH₃CH₂OH = ethanol
CH₃COCH₃ = propanone (acetone)
CH₃CH₂COOH = propanoic acid
Name the compound: CH₃CH(OH)CH₂CH₂CH₃
Step 1: Identify the longest chain:
The longest continuous carbon chain has 5 carbons: pent-
Step 2: Identify functional groups:
There is an -OH group (alcohol), so the suffix will be -ol
The compound is a pentanol
Step 3: Number the chain:
Number from the end closest to the -OH group
CH₃-CH(OH)-CH₂-CH₂-CH₃
Numbering left to right: 1-2-3-4-5
The -OH is on carbon 2
Step 4: Assemble the name:
Parent: pentan
Position of -OH: 2
Suffix: -ol
Final name: pentan-2-ol
(Also acceptable: 2-pentanol)
Name the following compound and explain your reasoning: CH₃CH₂CH(Cl)CH₂CH₃
Step-by-step solution:
1. Longest chain: The longest continuous carbon chain has 5 carbons, so the parent is pentane.
2. Functional groups: There is a chlorine atom attached, making this a chloroalkane. Halogens are named as prefixes: chloro-
3. Numbering: Since there's no high-priority functional group, number from the end that gives the substituent the lowest number.
From left: CH₃(1)-CH₂(2)-CH(Cl)(3)-CH₂(4)-CH₃(5) → Cl is on carbon 3
From right: CH₃(5)-CH₂(4)-CH(Cl)(3)-CH₂(2)-CH₃(1) → Cl is still on carbon 3
Either way, the chlorine is on carbon 3.
4. Final name: 3-chloropentane
Explanation: We use the prefix "chloro" to indicate the chlorine substituent, the number "3" to show its position, and "pentane" as the parent alkane. The name is written as one word with a hyphen between the number and the name: 3-chloropentane.
Isomers are compounds with the same molecular formula but different structural arrangements. Understanding the types of isomers is essential for predicting properties and reactions.
Definition: Isomers that differ in the arrangement of the carbon skeleton. The carbon chain has a different branching pattern.
Example: C₅H₁₂ (three chain isomers)
1. Pentane (straight chain):
CH₃-CH₂-CH₂-CH₂-CH₃
2. 2-methylbutane (one branch):
CH₃-CH(CH₃)-CH₂-CH₃
3. 2,2-dimethylpropane (two branches):
CH₃-C(CH₃)₂-CH₃
Properties: Chain isomers have different physical properties (boiling points, melting points) because branching affects molecular shape and surface area. More branching generally means lower boiling point due to reduced surface contact between molecules.
Key point: Same molecular formula (C₅H₁₂), different carbon skeleton arrangement.
Definition: Isomers that have the same carbon skeleton but differ in the position of a functional group or substituent.
Example: C₃H₈O (two position isomers - alcohols)
1. Propan-1-ol (-OH on carbon 1):
CH₃-CH₂-CH₂-OH
2. Propan-2-ol (-OH on carbon 2):
CH₃-CH(OH)-CH₃
Another example: C₄H₈ (alkenes)
1. But-1-ene (double bond between C1 and C2):
CH₂=CH-CH₂-CH₃
2. But-2-ene (double bond between C2 and C3):
CH₃-CH=CH-CH₃
Properties: Position isomers often have different chemical properties because the functional group is in a different environment. For example, propan-1-ol can be oxidized to an aldehyde, while propan-2-ol oxidizes to a ketone.
Key point: Same molecular formula, same carbon skeleton, different functional group position.
Definition: Isomers that have different functional groups, resulting in completely different chemical properties.
Common examples:
1. Alcohols vs Ethers (C₂H₆O):
Ethanol (alcohol): CH₃-CH₂-OH
Methoxymethane (ether): CH₃-O-CH₃
Very different properties: ethanol is polar and forms hydrogen bonds, while ether cannot hydrogen bond as effectively
2. Aldehydes vs Ketones (C₃H₆O):
Propanal (aldehyde): CH₃-CH₂-CHO
Propanone (ketone): CH₃-CO-CH₃
Different reactivity: aldehydes are easily oxidized, ketones are not
3. Carboxylic Acids vs Esters (C₃H₆O₂):
Propanoic acid: CH₃-CH₂-COOH
Methyl ethanoate: CH₃-COO-CH₃
Acid is acidic and corrosive, ester is neutral and often fragrant
Properties: Functional group isomers have dramatically different chemical and physical properties because they contain different functional groups. They belong to different homologous series.
Key point: Same molecular formula, completely different functional groups.
Draw all structural isomers of C₄H₁₀ and identify which type of isomerism is present. Name each isomer.
Type of isomerism:
These will be chain isomers (structural isomers) because C₄H₁₀ is an alkane with no functional groups—the only way to create isomers is by changing the carbon skeleton.
Isomer 1: Straight chain (4 carbons in a row)
Structure: CH₃-CH₂-CH₂-CH₃
Name: Butane
Isomer 2: Branched chain (3 carbons in main chain, 1 branch)
Structure: CH₃-CH(CH₃)-CH₃
(A methyl group branches off the middle carbon)
Name: 2-methylpropane (also called isobutane)
Total isomers:
C₄H₁₀ has 2 structural isomers
You cannot make more isomers by numbering differently—these are the only two distinct structures for C₄H₁₀.
Draw and name three different isomers of C₃H₈O. Identify what type of isomerism each pair represents.
Three isomers of C₃H₈O:
Isomer 1: Propan-1-ol (primary alcohol)
Structure: CH₃-CH₂-CH₂-OH
The -OH group is on carbon 1 (end of chain)
Isomer 2: Propan-2-ol (secondary alcohol)
Structure: CH₃-CH(OH)-CH₃
The -OH group is on carbon 2 (middle of chain)
Isomer 3: Methoxymethane (ether)
Structure: CH₃-O-CH₃
An oxygen atom is between two methyl groups (ether functional group)
Types of isomerism:
Propan-1-ol vs Propan-2-ol: Position isomers
They have the same carbon skeleton (3 carbons in a row) and the same functional group (-OH), but the -OH is in different positions.
Propan-1-ol vs Methoxymethane: Functional group isomers
They have the same molecular formula but completely different functional groups: one is an alcohol (-OH) and the other is an ether (C-O-C). They have very different properties.
Propan-2-ol vs Methoxymethane: Functional group isomers
Same reasoning as above—different functional groups.
Alkanes are saturated hydrocarbons containing only single C-C and C-H bonds. They undergo substitution reactions where hydrogen atoms are replaced by other atoms or groups.
General formula: CnH2n+2 (for straight-chain and branched alkanes)
Bonding: All carbon atoms are sp³ hybridized with tetrahedral geometry (bond angles ≈109.5°). Only single bonds present (sigma bonds only).
Physical properties:
Chemical properties:
Why alkanes are unreactive: The C-H bond is strong (413 kJ/mol) and non-polar. The electron density is evenly distributed, providing no reactive sites for electrophiles or nucleophiles to attack.
Definition: A reaction where one atom or group is replaced by another atom or group. For alkanes, hydrogen atoms are substituted by halogen atoms.
General equation:
Example - Chlorination of methane:
Methane + Chlorine → Chloromethane + Hydrogen chloride
Critical requirement: UV light or sunlight
Without UV light, alkanes do not react with halogens at room temperature. UV light provides the activation energy to break the Cl-Cl bond, initiating the reaction through a free radical mechanism.
Further substitution is possible:
CH₃Cl + Cl₂ → CH₂Cl₂ + HCl (dichloromethane)
CH₂Cl₂ + Cl₂ → CHCl₃ + HCl (trichloromethane, chloroform)
CHCl₃ + Cl₂ → CCl₄ + HCl (tetrachloromethane)
Controlling the product: Use excess alkane to favor monosubstitution, or excess halogen to drive multiple substitution.
The substitution occurs via a free radical chain reaction with three stages:
1. Initiation: UV light breaks the Cl-Cl bond homolytically (each atom takes one electron)
Cl₂ → 2Cl• (chlorine radicals)
2. Propagation: Chain reaction producing products and regenerating radicals
CH₄ + Cl• → •CH₃ + HCl
•CH₃ + Cl₂ → CH₃Cl + Cl•
(The Cl• radical is regenerated, allowing the chain to continue)
3. Termination: Radicals combine, ending the chain
Cl• + Cl• → Cl₂
•CH₃ + Cl• → CH₃Cl
•CH₃ + •CH₃ → C₂H₆
Why UV light is essential: The Cl-Cl bond (243 kJ/mol) is strong enough that thermal energy at room temperature cannot break it. UV light provides photons with sufficient energy to cause homolytic fission, generating the chlorine radicals needed to initiate the chain reaction.
Write a balanced equation for the reaction between propane and bromine in the presence of UV light. Name the organic product formed in the first substitution.
Equation:
Or more explicitly:
Product name:
The main organic product is 1-bromopropane
(Also called bromopropane since the position of Br can also be on carbon 2, forming 2-bromopropane as a minor product)
Important notes:
1. UV light must be shown above the arrow
2. Multiple products are possible: both 1-bromopropane and 2-bromopropane form
3. HBr is produced as a by-product
4. Further substitution can occur with excess Br₂
Explain why alkanes are unreactive under normal conditions but react with halogens in the presence of UV light. What role does UV light play in the reaction?
Why alkanes are unreactive:
Alkanes contain only C-C and C-H single bonds, which are both strong and non-polar. The C-H bond has a bond energy of approximately 413 kJ/mol, making it difficult to break under normal conditions. Additionally, the even distribution of electron density in alkane molecules means there are no partial positive or negative charges for other reagents to attack. This makes alkanes resistant to reaction with acids, bases, oxidizing agents, and even halogens at room temperature.
Why UV light enables reaction with halogens:
Halogens like Cl₂ and Br₂ have covalent bonds that are strong enough (Cl-Cl: 243 kJ/mol, Br-Br: 193 kJ/mol) that they don't break spontaneously at room temperature. UV light provides high-energy photons that can break the halogen-halogen bond through homolytic fission—each atom takes one electron from the shared pair, creating two highly reactive free radicals:
Cl₂ → 2Cl•
Role of UV light:
UV light acts as an initiator for the free radical chain reaction. The chlorine radicals (Cl•) are extremely reactive because they have an unpaired electron. These radicals can abstract hydrogen atoms from alkanes, breaking the C-H bond and forming new radicals that continue the chain reaction:
Cl• + CH₄ → •CH₃ + HCl
•CH₃ + Cl₂ → CH₃Cl + Cl•
Once initiated, the reaction becomes self-sustaining through the propagation steps, where new radicals are constantly generated. Without UV light, the initial radicals never form, so the reaction cannot proceed. This is why you must always indicate "UV light" or "sunlight" above the arrow when writing halogenation equations for alkanes—it's an essential condition, not just a detail.
Alkenes are unsaturated hydrocarbons containing at least one C=C double bond. They are much more reactive than alkanes and undergo addition reactions across the double bond.
General formula: CnH2n (for alkenes with one double bond)
Bonding: The C=C double bond consists of one sigma (σ) bond and one pi (π) bond. Carbon atoms in the double bond are sp² hybridized with trigonal planar geometry (bond angles ≈120°). The pi bond is weaker than the sigma bond.
Physical properties:
Chemical properties:
Why alkenes are reactive: The pi bond electrons are more exposed (above and below the molecular plane) than sigma bond electrons, making them accessible to electrophiles. Breaking the pi bond releases energy, which drives addition reactions.
Definition: A reaction where two atoms or groups add across the C=C double bond. The pi bond breaks and two new sigma bonds form.
General pattern:
1. Hydrogenation (Addition of H₂):
Converts alkenes to alkanes
Requires catalyst: Ni, Pt, or Pd
Example:
Ethene + Hydrogen → Ethane
Used industrially to convert vegetable oils (unsaturated) to margarine (saturated)
2. Halogenation (Addition of X₂):
Adds two halogen atoms across the double bond
No catalyst needed, occurs at room temperature
Example:
Ethene + Bromine → 1,2-dibromoethane
Test for unsaturation: bromine water decolorizes (brown → colorless) when alkene is present
3. Hydration (Addition of H₂O):
Adds H and OH across the double bond to form an alcohol
Requires acid catalyst (H₂SO₄ or H₃PO₄) and heat
Example:
Ethene + Water → Ethanol
Industrial method for producing ethanol
4. Hydrohalogenation (Addition of HX):
Adds H and halogen across the double bond
Example:
Ethene + Hydrogen bromide → Bromoethane
The rule: In the addition of HX or H₂O to an unsymmetrical alkene, the hydrogen atom adds to the carbon of the double bond that already has more hydrogen atoms.
Simple version: "The rich get richer" - hydrogen goes to the carbon with more hydrogens.
Why it matters: For symmetrical alkenes like ethene (CH₂=CH₂), it doesn't matter which carbon gets H and which gets X - you get the same product either way. But for unsymmetrical alkenes like propene (CH₃-CH=CH₂), there are two possible products, and Markovnikov's rule predicts which one forms predominantly.
Example: Hydration of propene
Propene structure: CH₃-CH=CH₂
Left carbon of double bond: has 1 H (the CH group)
Right carbon of double bond: has 2 H (the CH₂ group)
By Markovnikov's rule: H adds to the CH₂ carbon (which already has more H)
Therefore: OH adds to the CH carbon
Product: CH₃-CH(OH)-CH₃ = propan-2-ol (major product)
NOT CH₃-CH₂-CH₂OH (propan-1-ol, which is the minor product)
Another example: Hydrochlorination of but-1-ene
But-1-ene: CH₃-CH₂-CH=CH₂
Double bond between C3 and C4
C3 has 1 H, C4 has 2 H
H adds to C4, Cl adds to C3
Product: CH₃-CH₂-CHCl-CH₃ = 2-chlorobutane (major)
Mechanism explanation (extension): The rule works because addition proceeds through the most stable carbocation intermediate. Secondary and tertiary carbocations are more stable than primary carbocations. When H⁺ adds to the carbon with more H, it forms a carbocation on the carbon with more alkyl groups (more substituted), which is more stable.
Predict the major product when but-2-ene (CH₃-CH=CH-CH₃) reacts with: (a) hydrogen in the presence of a nickel catalyst, (b) bromine water. Name each product.
(a) Hydrogenation:
Reaction:
The double bond is converted to a single bond by adding H₂
Product: Butane
Note: Markovnikov's rule doesn't apply here because H₂ adds symmetrically—one H to each carbon of the double bond.
(b) Bromination (bromine water):
Reaction:
One Br adds to each carbon of the double bond
Product: 2,3-dibromobutane
Observation: The brown color of bromine water disappears (decolorizes), confirming the presence of an alkene.
Note: Markovnikov's rule doesn't apply because Br₂ adds symmetrically.
Using Markovnikov's rule, predict the major product when propene (CH₃-CH=CH₂) reacts with HBr. Write the equation and name the product. Explain your reasoning.
Step 1: Identify the double bond carbons
Propene structure: CH₃-CH=CH₂
Left carbon of double bond (C2): bonded to 1 hydrogen (part of CH group)
Right carbon of double bond (C3): bonded to 2 hydrogens (CH₂ group)
Step 2: Apply Markovnikov's rule
"Hydrogen adds to the carbon with more hydrogens"
The CH₂ carbon already has 2 H atoms, so the H from HBr adds there
The Br adds to the other carbon (the CH carbon)
Step 3: Draw the product
H adds to C3: CH₃-CH-CH₃ (with H on the right carbon)
Br adds to C2: CH₃-CHBr-CH₃
Equation:
Product name:
2-bromopropane
Explanation:
According to Markovnikov's rule, in the addition of HBr to an unsymmetrical alkene, the hydrogen atom attaches to the carbon of the double bond that already has more hydrogen atoms. In propene, C3 (the CH₂ group) has more hydrogen atoms than C2 (the CH group), so H adds to C3 and Br adds to C2, forming 2-bromopropane as the major product.
The alternative product, 1-bromopropane (CH₃-CH₂-CH₂Br), would form if Br added to C3 instead, but this is the minor product because it violates Markovnikov's rule. The major product is always the one predicted by Markovnikov's rule.
Alcohols contain the hydroxyl (-OH) functional group bonded to a saturated carbon atom. They are classified by the number of carbon atoms bonded to the carbon bearing the -OH group, which determines their oxidation behavior.
Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°) based on how many carbon atoms are directly bonded to the carbon bearing the -OH group.
Primary (1°) alcohol: The carbon with -OH is bonded to ONE other carbon (or zero carbons for methanol)
General structure: R-CH₂-OH
Example: Ethanol CH₃-CH₂-OH
The carbon with -OH is bonded to one other carbon (the CH₃)
Secondary (2°) alcohol: The carbon with -OH is bonded to TWO other carbons
General structure: R₂-CH-OH
Example: Propan-2-ol CH₃-CH(OH)-CH₃
The carbon with -OH is bonded to two other carbons (two CH₃ groups)
Tertiary (3°) alcohol: The carbon with -OH is bonded to THREE other carbons
General structure: R₃-C-OH
Example: 2-methylpropan-2-ol (CH₃)₃C-OH
The carbon with -OH is bonded to three other carbons (three CH₃ groups)
Key point: Count the carbons bonded to the C-OH carbon, NOT the total number of carbons in the molecule. Ignore hydrogens when classifying.
Alcohols can be oxidized using oxidizing agents such as acidified potassium dichromate (K₂Cr₂O₇/H⁺) or acidified potassium permanganate (KMnO₄/H⁺). The color change from orange (Cr₂O₇²⁻) to green (Cr³⁺) indicates oxidation has occurred.
Primary alcohol oxidation (2 steps possible):
Step 1: Primary alcohol → Aldehyde
Example: Ethanol → Ethanal
CH₃-CH₂-OH → CH₃-CHO
Step 2: Aldehyde → Carboxylic acid (with excess oxidizing agent)
Example: Ethanal → Ethanoic acid
CH₃-CHO → CH₃-COOH
Overall: Primary alcohol → Aldehyde → Carboxylic acid
To stop at the aldehyde stage, use gentle heating and distill the aldehyde as it forms (it has a lower boiling point). For full oxidation to the acid, use excess oxidizing agent and reflux.
Secondary alcohol oxidation (1 step only):
Secondary alcohol → Ketone
Example: Propan-2-ol → Propanone
CH₃-CH(OH)-CH₃ → CH₃-CO-CH₃
Ketones cannot be oxidized further under normal conditions (no H on the carbonyl carbon)
Tertiary alcohol oxidation:
No reaction under normal conditions
Tertiary alcohols resist oxidation because the C-OH carbon has no hydrogen atoms to remove
The dichromate solution remains orange (no color change)
Summary:
1° alcohol → Aldehyde → Carboxylic acid
2° alcohol → Ketone (stops here)
3° alcohol → No reaction
Dehydration: Removal of water (H₂O) from an alcohol to form an alkene.
Conditions: Concentrated sulfuric acid (H₂SO₄) or phosphoric acid (H₃PO₄) catalyst, heat (~170°C)
General equation:
Example: Dehydration of ethanol
Ethanol → Ethene + Water
Mechanism: The acid protonates the -OH group, turning it into a good leaving group (H₂O). Water leaves, forming a carbocation, then a hydrogen is removed from an adjacent carbon to form the double bond.
Note: This is the reverse of hydration of alkenes. Dehydration forms alkenes from alcohols, while hydration forms alcohols from alkenes.
Fermentation: The anaerobic breakdown of glucose by yeast to produce ethanol and carbon dioxide.
Equation:
Glucose → Ethanol + Carbon dioxide
Conditions:
Process: Yeast cells contain enzymes that catalyze the breakdown of glucose. The process stops when ethanol concentration reaches about 15% because the alcohol denatures the yeast enzymes.
Applications:
Comparison with hydration of ethene: Fermentation is a biological process using renewable glucose from plants, while hydration uses ethene from petroleum (non-renewable). Fermentation is slower but more sustainable.
Classify the following alcohols as primary, secondary, or tertiary. Then predict the oxidation product(s) for each: (a) Butan-1-ol: CH₃CH₂CH₂CH₂OH, (b) Butan-2-ol: CH₃CH(OH)CH₂CH₃, (c) 2-methylpropan-2-ol: (CH₃)₃COH
(a) Butan-1-ol: CH₃CH₂CH₂CH₂OH
Classification: Primary (1°) alcohol
Reason: The carbon bearing the -OH group is bonded to only ONE other carbon
Oxidation products:
First oxidation: Butanal (CH₃CH₂CH₂CHO) - an aldehyde
Further oxidation: Butanoic acid (CH₃CH₂CH₂COOH) - a carboxylic acid
(b) Butan-2-ol: CH₃CH(OH)CH₂CH₃
Classification: Secondary (2°) alcohol
Reason: The carbon bearing the -OH group is bonded to TWO other carbons
Oxidation product:
Butanone (CH₃COCH₂CH₃) - a ketone
No further oxidation occurs; ketones are resistant to oxidation
(c) 2-methylpropan-2-ol: (CH₃)₃COH
Classification: Tertiary (3°) alcohol
Reason: The carbon bearing the -OH group is bonded to THREE other carbons
Oxidation product:
No reaction
Tertiary alcohols cannot be oxidized under normal conditions. The dichromate solution would remain orange.
Explain why primary alcohols can be oxidized to two different products (aldehyde and carboxylic acid), while secondary alcohols can only be oxidized to one product (ketone). Include the structural reason for this difference.
Primary alcohols - two oxidation steps:
When a primary alcohol is oxidized, it first loses two hydrogen atoms (one from the -OH and one from the C-OH carbon) to form an aldehyde. The aldehyde has the structure R-CHO, where the carbonyl carbon still has ONE hydrogen atom attached.
Because this hydrogen is still present on the carbonyl carbon, the aldehyde can be oxidized further. It gains an oxygen atom and loses the hydrogen, forming a carboxylic acid (R-COOH).
Key point: The aldehyde intermediate has a H on the carbonyl carbon, making further oxidation possible.
Secondary alcohols - one oxidation step:
When a secondary alcohol is oxidized, it loses two hydrogen atoms to form a ketone with the structure R₂C=O. The carbonyl carbon in a ketone is bonded to TWO carbon atoms and has NO hydrogen atoms.
Because there is no hydrogen on the carbonyl carbon, further oxidation cannot occur under normal conditions. To oxidize a ketone would require breaking strong C-C bonds, which needs very harsh conditions and would destroy the molecule.
Key point: Ketones have NO hydrogen on the carbonyl carbon, so they resist further oxidation.
Structural explanation:
Oxidation of organic compounds typically involves removing hydrogen atoms from a carbon and adding oxygen or oxygen-containing groups. For oxidation to occur easily, there must be a hydrogen atom available on the carbon being oxidized.
- Primary alcohol (R-CH₂-OH): Has 2 H on C-OH carbon → oxidizes to aldehyde (R-CHO) which has 1 H → oxidizes to carboxylic acid (R-COOH) which has 0 H
- Secondary alcohol (R₂CH-OH): Has 1 H on C-OH carbon → oxidizes to ketone (R₂C=O) which has 0 H → cannot oxidize further
- Tertiary alcohol (R₃C-OH): Has 0 H on C-OH carbon → cannot oxidize at all
Understanding the differences between fossil fuels and biofuels is essential for evaluating sustainable energy options. The comparison focuses on energy density, carbon neutrality, and environmental impact.
Definition: Fuels formed from the remains of ancient organisms over millions of years. Main examples: coal, petroleum (crude oil), natural gas.
Composition: Primarily hydrocarbons (compounds of carbon and hydrogen). Petrol, diesel, and kerosene are refined from crude oil.
Combustion: Fossil fuels combust completely in excess oxygen to produce CO₂ and H₂O, releasing energy:
Example for octane (component of petrol):
Advantages:
Disadvantages:
Definition: Ethanol (C₂H₅OH) produced from renewable biological sources through fermentation of plant materials.
Production: Fermentation of glucose from crops (sugar cane, corn, wheat)
Combustion:
Advantages:
Disadvantages:
Definition: A fuel is carbon neutral if the amount of CO₂ released during combustion equals the amount of CO₂ absorbed from the atmosphere during production.
Why bioethanol is considered carbon neutral:
Step 1 - Plant growth (CO₂ absorption):
Plants absorb CO₂ from the atmosphere during photosynthesis to produce glucose:
Step 2 - Fermentation (no net CO₂ to atmosphere):
This CO₂ was just absorbed from atmosphere, so it's being returned
Step 3 - Combustion (CO₂ released):
Overall carbon cycle:
CO₂ absorbed (photosynthesis) = CO₂ released (fermentation + combustion)
Net change in atmospheric CO₂ = zero
Why fossil fuels are NOT carbon neutral:
Fossil fuels release carbon that was locked underground for millions of years. This carbon was removed from the atmosphere long ago, so burning fossil fuels adds NEW carbon to the current atmosphere, increasing total atmospheric CO₂.
Reality check: Bioethanol is not perfectly carbon neutral because:
However, bioethanol is still much closer to carbon neutral than fossil fuels, with ~70-90% reduction in net CO₂ emissions.
Energy density: The amount of energy released per unit mass or volume of fuel.
Approximate values:
Implication: Ethanol has about 66% of petrol's energy density (by volume). This means:
Why the difference? Ethanol already contains oxygen (C₂H₅OH), so it releases less energy when combusted compared to pure hydrocarbons which must gain all their oxygen from air during combustion.
Explain why bioethanol is considered carbon neutral while petrol is not. Use equations to support your explanation.
Bioethanol - Carbon neutral cycle:
1. Plant growth (CO₂ absorbed from atmosphere):
2. Fermentation (some CO₂ released back):
3. Combustion (remaining carbon released as CO₂):
Net result: All the carbon in bioethanol came from atmospheric CO₂ absorbed during recent plant growth (this growing season). When bioethanol burns, it returns this CO₂ to the atmosphere. Since the CO₂ released equals the CO₂ absorbed (within the same year or few years), there is no net increase in atmospheric CO₂. The carbon simply cycles: atmosphere → plant → ethanol → atmosphere.
Petrol - NOT carbon neutral:
Combustion of octane (petrol component):
Carbon source: The carbon in petrol was locked underground as fossil remains for millions of years. This carbon was removed from the atmosphere millions of years ago when ancient organisms photosynthesized and then died.
Net result: Burning petrol takes carbon that has been out of circulation for millions of years and puts it back into the current atmosphere. This represents a NET ADDITION of CO₂ to the present atmosphere. The carbon is not being recycled from recent photosynthesis—it's ancient carbon being added to the modern carbon cycle, causing atmospheric CO₂ to increase.
Key difference: Bioethanol cycles carbon over months/years (carbon neutral), while fossil fuels add ancient stored carbon to today's atmosphere (not carbon neutral).
Compare the advantages and disadvantages of bioethanol versus petrol as vehicle fuels. In your answer, discuss energy density and environmental impact.
Advantages of bioethanol over petrol:
1. Carbon neutrality: Bioethanol is renewable and approximately carbon neutral because the CO₂ released during combustion was recently absorbed from the atmosphere during plant photosynthesis. This creates a closed carbon cycle with no net addition of CO₂ to the atmosphere. In contrast, petrol adds ancient carbon to the atmosphere, contributing to climate change.
2. Cleaner combustion: Bioethanol produces fewer harmful pollutants such as sulfur dioxide (SO₂) and particulates because plant-derived ethanol doesn't contain sulfur compounds that are present in petroleum. This reduces acid rain and air pollution.
3. Renewable resource: Crops for bioethanol can be grown annually, making it a renewable fuel source, whereas petroleum reserves are finite and non-renewable.
Disadvantages of bioethanol compared to petrol:
1. Lower energy density: Bioethanol has an energy density of approximately 24 MJ/L compared to petrol's 35 MJ/L—only about 66% of petrol's energy content by volume. This means:
2. Land use concerns: Large areas of agricultural land are needed to grow crops for bioethanol production. This can:
3. Production energy requirements: Growing crops requires fertilizers, farm machinery, harvesting, transportation, and fermentation—all of which require energy input. While bioethanol is much better than petrol, it's not perfectly carbon neutral when these factors are considered.
4. Cost: Currently, bioethanol is more expensive to produce than petrol from crude oil, though this may change as petroleum becomes scarcer and renewable technology improves.
Conclusion:
Bioethanol offers significant environmental benefits, particularly in reducing net CO₂ emissions and air pollutants. However, its lower energy density and land use requirements present practical challenges. The ideal solution may involve a combination of improved biofuel technology, increased engine efficiency, and a transition to multiple renewable energy sources rather than relying solely on either fuel type.
Esters are organic compounds with the functional group -COO-. They are formed by the reaction between carboxylic acids and alcohols, and are known for their pleasant, fruity aromas.
General structure: R-COO-R' where R and R' are alkyl groups
Functional group: The ester linkage (-COO-) consists of a carbonyl group (C=O) bonded to an oxygen atom, which is bonded to another carbon.
Properties:
Examples:
Ethyl ethanoate (ethyl acetate): CH₃-COO-CH₂CH₃ - nail polish remover smell
Methyl butanoate: CH₃CH₂CH₂-COO-CH₃ - apple/pineapple aroma
Pentyl ethanoate: CH₃-COO-C₅H₁₁ - banana aroma
Definition: The condensation reaction between a carboxylic acid and an alcohol to form an ester and water.
General equation:
Or more explicitly:
Example: Formation of ethyl ethanoate
Ethanoic acid + Ethanol ⇌ Ethyl ethanoate + Water
Conditions for esterification:
Why reflux? Esterification is slow and reversible. Heating speeds up the reaction, but alcohols and esters have low boiling points and would evaporate. Reflux allows heating while preventing loss of materials - vapors condense and return to the reaction flask.
Why remove water? Esterification is an equilibrium reaction. Removing water (one of the products) shifts equilibrium to the right, increasing ester yield.
Rule: The alcohol part becomes the start (-yl suffix), and the acid part becomes the end (-oate suffix).
Pattern: [Alcohol-yl] + [Acid-oate]
Step-by-step naming:
1. Identify the alcohol side (R'-O-) - name it with -yl ending
2. Identify the acid side (R-COO-) - name it with -oate ending
3. Combine: [alcohol name-yl] + [acid name-oate]
Examples:
Example 1: CH₃-COO-CH₂CH₃
Alcohol side: -CH₂CH₃ (from ethanol) → ethyl
Acid side: CH₃-COO- (from ethanoic acid) → ethanoate
Name: Ethyl ethanoate
Example 2: CH₃CH₂-COO-CH₃
Alcohol side: -CH₃ (from methanol) → methyl
Acid side: CH₃CH₂-COO- (from propanoic acid) → propanoate
Name: Methyl propanoate
Example 3: CH₃-COO-CH₂CH₂CH₃
Alcohol side: -CH₂CH₂CH₃ (from propan-1-ol) → propyl
Acid side: CH₃-COO- (from ethanoic acid) → ethanoate
Name: Propyl ethanoate
Common mistake: Naming it backwards (acid-yl alcohol-oate) - always check that the alcohol part comes first!
Critical safety feature: The reflux apparatus must have an open top condenser - never sealed, or pressure builds up and the apparatus explodes!
Key components of a reflux setup:
Why water enters at bottom: Ensures the entire condenser is filled with cold water for maximum cooling efficiency. If water entered at top, only the top would cool properly.
How it works:
1. Mixture is heated and vaporizes
2. Vapor rises into the condenser
3. Cold water jacket cools the vapor, condensing it back to liquid
4. Liquid drips back into the flask
5. Volatile components don't escape, but pressure can escape through open top
When drawing reflux apparatus:
(a) Write a balanced equation for the formation of propyl methanoate from the appropriate carboxylic acid and alcohol. (b) Name the conditions required. (c) Explain why reflux is used rather than simple heating.
(a) Equation:
Step 1: Identify the reactants from the ester name
Propyl methanoate = propyl (from propan-1-ol) + methanoate (from methanoic acid)
Step 2: Write the structures
Methanoic acid: H-COOH
Propan-1-ol: CH₃CH₂CH₂OH
Propyl methanoate: H-COO-CH₂CH₂CH₃
Step 3: Write the balanced equation
or
(b) Conditions:
1. Catalyst: Concentrated sulfuric acid (conc. H₂SO₄)
2. Reflux (heat under reflux conditions)
3. Remove water to shift equilibrium toward products
(c) Why reflux instead of simple heating:
Problem with simple heating: Both the alcohol (propan-1-ol, bp 97°C) and the ester product (propyl methanoate, bp ~80°C) have relatively low boiling points. If we simply heat the mixture in an open container, these volatile components would evaporate and escape, reducing the yield dramatically.
Why reflux solves this: The reflux apparatus has a vertical condenser above the reaction flask. When volatile components vaporize and rise, they encounter the cold condenser walls and condense back to liquid, dripping back into the flask. This allows us to heat the reaction mixture to speed up the rate while preventing loss of reactants and products.
Additional benefit: The reflux setup has an open top, which prevents dangerous pressure buildup while still containing the volatile components through condensation.
A student wants to prepare methyl butanoate. (a) Name the carboxylic acid and alcohol required. (b) Explain why concentrated sulfuric acid is added to the reaction mixture. (c) Describe how to maximize the yield of ester.
(a) Reactants required:
Breaking down the ester name: "Methyl butanoate"
- "Methyl" comes from the alcohol → Methanol (CH₃OH)
- "Butanoate" comes from the carboxylic acid → Butanoic acid (CH₃CH₂CH₂COOH)
Reactants: Butanoic acid and methanol
(b) Role of concentrated sulfuric acid:
Concentrated sulfuric acid serves two important roles:
1. Catalyst: H₂SO₄ acts as an acid catalyst that speeds up the esterification reaction. Esterification is naturally very slow at room temperature. The acid catalyst protonates the carbonyl oxygen of the carboxylic acid, making the carbon more susceptible to nucleophilic attack by the alcohol, thus accelerating the reaction.
2. Dehydrating agent: Concentrated H₂SO₄ is hygroscopic (absorbs water). Since esterification is a reversible reaction that produces water as a byproduct, removing the water shifts the equilibrium to the right (toward products) according to Le Chatelier's principle, increasing ester yield.
(c) Maximizing ester yield:
1. Use reflux conditions: Heat the reaction mixture under reflux to speed up the reaction while preventing loss of volatile reactants and products. The condenser must have water entering at the bottom and exiting at the top, with an open top to prevent pressure buildup.
2. Remove water continuously: Since esterification is an equilibrium reaction, removing the water product as it forms shifts equilibrium to the right (Le Chatelier's principle), increasing the yield of ester. This can be done using:
3. Use excess reactant: Using an excess of either the alcohol or the carboxylic acid will shift equilibrium toward products. Since methanol is cheaper and more readily available than butanoic acid, using excess methanol is economically sensible.
4. Allow sufficient reaction time: Esterification can be slow even with heating and catalyst, so refluxing for an extended period (several hours) allows the reaction to approach equilibrium.
Soaps and detergents are surfactants that clean by emulsifying grease and oils in water. Understanding their structure and mechanism of action explains both how they work and why detergents perform better than soaps in hard water.
Key structural feature: Both soaps and detergents have a dual nature - one end is hydrophilic (water-loving) and the other end is hydrophobic (water-fearing).
Soap structure:
Hydrophobic tail: Long hydrocarbon chain (12-18 carbons), non-polar
Drawn as a zig-zag line or wavy line
Hydrophilic head: Carboxylate ion (-COO⁻), ionic, polar
Drawn as a circle with negative charge
Example: Sodium stearate CH₃(CH₂)₁₆COO⁻Na⁺
Detergent structure:
Hydrophobic tail: Long hydrocarbon chain, similar to soap
Hydrophilic head: Sulfonate group (-SO₃⁻) or sulfate group (-OSO₃⁻), ionic
Example: Sodium dodecylbenzenesulfonate (LAS)
Why this dual nature matters:
The hydrophobic tail dissolves in grease/oil
The hydrophilic head dissolves in water
This allows soap/detergent molecules to bridge the grease-water interface
Emulsification: The process of dispersing grease/oil droplets throughout water using soap or detergent.
How cleaning works - step by step:
Step 1: Soap molecules surround grease
When soap/detergent is added to water containing grease, the hydrophobic tails are attracted to the grease while the hydrophilic heads remain in the water.
Step 2: Micelle formation
Soap/detergent molecules arrange themselves around the grease droplet with:
- Hydrophobic tails pointing INWARD (into the grease droplet)
- Hydrophilic heads pointing OUTWARD (toward the water)
This spherical structure is called a micelle
Step 3: Grease disperses in water
The micelles have charged surfaces (from the hydrophilic heads), so they repel each other and remain suspended in water rather than clumping together. The grease is now emulsified - dispersed as tiny droplets throughout the water.
Step 4: Rinse away
The water (containing suspended micelles with grease trapped inside) can be rinsed away, removing the grease from the surface being cleaned.
CRITICAL for Band 6: Drawing micelles
When drawing a micelle diagram:
Common mistake: Drawing tails pointing outward - this is wrong! The tails must be INSIDE the grease because they are hydrophobic (grease-loving, water-hating).
Hard water: Water containing dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions, typically from limestone regions.
How soaps react with hard water:
Soap molecules (carboxylate ions) react with Ca²⁺ and Mg²⁺ ions to form insoluble precipitates:
Stearate ion + Calcium ion → Calcium stearate (solid)
Problems caused:
Why detergents don't form scum:
Detergents have sulfonate (-SO₃⁻) or sulfate (-OSO₃⁻) heads instead of carboxylate (-COO⁻) heads. The calcium and magnesium salts of these groups are SOLUBLE in water, so no precipitate forms.
Detergent + Calcium ion → Soluble calcium salt (no scum!)
Advantage of detergents: Work effectively in both soft and hard water, no scum formation, more efficient cleaning in hard water areas.
Explain how soap removes grease from a dirty plate. In your answer, describe the structure of soap molecules and the formation of micelles. Include a labeled diagram.
Structure of soap molecules:
Soap molecules have a dual structure:
1. Hydrophobic tail: A long hydrocarbon chain (typically 12-18 carbons) that is non-polar and water-repelling. This tail is attracted to grease and oils because they are also non-polar ("like dissolves like").
2. Hydrophilic head: An ionic carboxylate group (-COO⁻) that is polar and water-attracting. This head dissolves readily in water.
This dual nature allows soap to interact with both grease and water.
How soap removes grease:
Step 1: When soapy water contacts grease on the plate, soap molecules are attracted to the grease. The hydrophobic tails dissolve into the grease while the hydrophilic heads remain in the water.
Step 2: As more soap molecules accumulate, they arrange themselves around the grease droplet, forming a structure called a micelle. In a micelle:
- Hydrophobic tails point INWARD, buried inside the grease droplet
- Hydrophilic heads point OUTWARD, facing the surrounding water
Step 3: The grease is now surrounded by a layer of soap molecules with charged heads on the outside. This makes the grease droplet (with its soap coating) soluble in water.
Step 4: The micelles repel each other due to their charged surfaces, keeping the grease droplets dispersed throughout the water rather than clumping together. This process is called emulsification.
Step 5: When you rinse the plate, the water carries away the micelles (with grease trapped inside), leaving the plate clean.
Labeled diagram of a micelle:
[In an exam, you would draw:]
- A circle representing the grease droplet in the center
- Zig-zag lines (hydrophobic tails) pointing INWARD into the grease
- Circles with - charges (hydrophilic heads) on the outer edge
- Water molecules (H₂O) surrounding the micelle
Labels:
- "Grease droplet" (center)
- "Hydrophobic tails inside grease"
- "Hydrophilic heads in water"
- "Water molecules"
Explain why soap forms scum in hard water but detergents do not. Include equations in your answer.
Why soap forms scum in hard water:
Hard water contains dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These ions are present in water that has passed through limestone or chalk regions, where minerals dissolve into the water.
Soap molecules have a carboxylate head (-COO⁻). When soap is added to hard water, the carboxylate ions react with Ca²⁺ and Mg²⁺ ions to form insoluble salts:
(Stearate ion + Calcium ion → Calcium stearate precipitate)
Similarly with magnesium:
The calcium and magnesium salts of soap are insoluble in water. They precipitate out as a gray, sticky solid called scum. This scum:
Why detergents do not form scum:
Detergents have a different hydrophilic head group - typically sulfonate (-SO₃⁻) or sulfate (-OSO₃⁻) instead of carboxylate (-COO⁻).
When detergents react with Ca²⁺ or Mg²⁺ ions, they also form salts:
(Detergent + Calcium ion → Calcium detergent salt)
However, the crucial difference is that calcium and magnesium salts of sulfonate/sulfate groups are soluble in water. They remain dissolved and do not precipitate, so no scum forms.
This means detergents:
Conclusion:
The difference in scum formation comes down to solubility. Soap forms insoluble Ca²⁺/Mg²⁺ salts (scum), while detergents form soluble Ca²⁺/Mg²⁺ salts (no scum). This is why detergents have largely replaced soaps for washing clothes and dishes, especially in areas with hard water.
Addition polymers are formed when alkene monomers undergo repeated addition reactions to form long chains. No small molecules are eliminated during the reaction—all atoms from the monomers are incorporated into the polymer.
Process: Addition polymerization involves breaking the C=C double bond in alkene monomers and forming new C-C single bonds between monomers to create a long chain.
General equation:
Where n = degree of polymerization (number of monomer units)
R = substituent group (H, CH₃, Cl, C₆H₅, etc.)
Key features:
Conditions:
Drawing polymer structures:
1. Remove the double bond from the monomer
2. Add bonds extending from each end carbon (shown as lines through brackets)
3. Enclose the repeating unit in brackets with subscript n
4. Example: CH₂=CH₂ becomes -(CH₂-CH₂)n- or more commonly shown as [-CH₂-CH₂-]n
Monomer: Ethene (ethylene), CH₂=CH₂
Polymerization reaction:
or shown as: [-CH₂-CH₂-]n
Two types of polyethylene:
1. LDPE (Low-Density Polyethylene):
2. HDPE (High-Density Polyethylene):
Why the difference? Different polymerization conditions (temperature, pressure, catalyst) produce different degrees of branching, which affects how closely the polymer chains can pack together.
Monomer: Chloroethene (vinyl chloride), CH₂=CHCl
Polymerization reaction:
or shown as: [-CH₂-CHCl-]n
Structure: Similar to polyethylene but every second carbon has a chlorine atom attached.
Properties:
Uses:
Environmental concern: When burned, PVC releases hydrogen chloride (HCl) gas and can produce toxic dioxins, making disposal problematic.
Monomer: Styrene (phenylethene), CH₂=CH-C₆H₅
Polymerization reaction:
or shown as: [-CH₂-CH(C₆H₅)-]n
Structure: Similar to polyethylene but every second carbon has a benzene ring (phenyl group) attached.
Two forms:
1. Solid polystyrene:
2. Expanded polystyrene (foam, Styrofoam™):
Advantages: Low cost, good insulation, lightweight
Disadvantages: Non-biodegradable, takes up large volume in landfills, releases styrene if burned
Monomer: Tetrafluoroethene, CF₂=CF₂
Polymerization reaction:
or shown as: [-CF₂-CF₂-]n
Structure: Similar to polyethylene but ALL hydrogen atoms are replaced by fluorine atoms.
Properties:
Uses:
Why it's non-stick: The C-F bonds are very strong and the fluorine atoms create a surface that has very weak intermolecular forces with other substances, so nothing sticks to it.
(a) Draw the structure of the monomer used to make polystyrene. (b) Write an equation for the polymerization reaction. (c) Explain why expanded polystyrene is used for packaging rather than solid polystyrene.
(a) Monomer structure:
Name: Styrene (also called phenylethene or vinylbenzene)
Structure: CH₂=CH-C₆H₅
or more explicitly:
CH₂=CH- (with a benzene ring attached to the second carbon)
The monomer contains a C=C double bond (ethene part) with a benzene ring (phenyl group) attached to one of the carbons.
(b) Polymerization equation:
Where:
- n = a very large number (thousands to millions)
- The C=C double bond breaks
- Monomers link through new C-C single bonds
- The benzene ring remains unchanged as a side group
(c) Why expanded polystyrene for packaging:
Structure of expanded polystyrene: Contains millions of tiny gas bubbles trapped within the polymer structure, making it approximately 95% air.
Advantages for packaging:
1. Lightweight: The high air content makes expanded polystyrene extremely light, reducing shipping costs and making packages easier to handle. Solid polystyrene would be much heavier and more expensive to transport.
2. Shock absorption: The air bubbles compress when impacted, absorbing shocks and protecting the packaged items from damage during transport. Solid polystyrene is rigid and brittle—it would transfer impacts directly to the packaged goods and could shatter.
3. Thermal insulation: Air is an excellent insulator. Expanded polystyrene keeps items at stable temperatures, which is important for food packaging and temperature-sensitive products. Solid polystyrene has no insulating air gaps.
4. Cost-effective: Expanded polystyrene uses less plastic material (more air, less polymer), making it cheaper to produce than solid polystyrene of the same volume.
5. Cushioning: The soft, compressible nature provides cushioning around fragile items, while solid polystyrene would provide no cushioning effect.
Compare LDPE and HDPE in terms of structure, properties, and uses. Explain the relationship between molecular structure and physical properties.
Structure differences:
LDPE (Low-Density Polyethylene): Has highly branched polymer chains. During polymerization under high pressure and temperature, side chains form off the main carbon backbone, creating a branched, tree-like structure.
HDPE (High-Density Polyethylene): Has linear polymer chains with minimal or no branching. Produced using special catalysts (Ziegler-Natta) at lower temperatures and pressures, resulting in straight-chain polymers.
How structure affects properties:
Chain packing: Linear HDPE chains can pack closely together in an ordered, crystalline arrangement, similar to how straight logs stack neatly. Branched LDPE chains cannot pack as closely because the branches create gaps and disorder, like trying to stack tree branches—there are many empty spaces.
Intermolecular forces: When polymer chains are close together (HDPE), the dispersion forces between chains are stronger because there's more surface contact. When chains are far apart (LDPE), intermolecular forces are weaker.
Property comparison:
Density:
Flexibility:
Melting point:
Tensile strength:
Uses based on properties:
LDPE uses: Applications requiring flexibility and transparency:
HDPE uses: Applications requiring rigidity and strength:
Structure-property relationship summary:
The key principle is that molecular structure determines how closely polymer chains can pack, which determines the strength of intermolecular forces, which determines physical properties. Branching in LDPE prevents tight packing → weaker forces → softer, more flexible, lower melting point. Linear structure in HDPE allows tight packing → stronger forces → harder, more rigid, higher melting point. This demonstrates how microscopic structure directly determines macroscopic properties.
Condensation polymers are formed when monomers join together with the elimination of a small molecule, usually water (H₂O). Unlike addition polymers, not all atoms from the monomers end up in the polymer chain.
Key features of condensation polymerization:
Difference from addition polymerization:
Addition: All atoms from monomer → polymer (no elimination)
Condensation: Monomer atoms → polymer + small molecule (H₂O)
Common types:
General pattern:
Monomer A + Monomer B → Polymer + H₂O (or other small molecule)
Formation: Condensation reaction between dicarboxylic acids and diols (dialcohols).
Functional groups involved:
Carboxylic acid: -COOH
Alcohol: -OH
Ester link formed: -COO-
General reaction:
Dicarboxylic acid + Diol → Polyester + Water
Example: PET (Polyethylene Terephthalate)
Monomers:
1. Terephthalic acid (benzene-1,4-dicarboxylic acid): HOOC-C₆H₄-COOH
2. Ethylene glycol (ethane-1,2-diol): HO-CH₂-CH₂-OH
How water is eliminated:
The -OH from the acid and an H from the alcohol combine to form H₂O
The remaining parts join to form an ester link (-COO-)
Properties of PET:
Uses:
Why it's called polyethylene terephthalate: The name comes from the two monomers—ethylene glycol and terephthalic acid.
Formation: Condensation reaction between dicarboxylic acids and diamines.
Functional groups involved:
Carboxylic acid: -COOH
Amine: -NH₂
Amide link formed: -CONH-
General reaction:
Dicarboxylic acid + Diamine → Polyamide + Water
Example: Nylon-6,6
Monomers:
1. Adipic acid (hexanedioic acid): HOOC-(CH₂)₄-COOH
(6 carbons total, hence "6" in the name)
2. Hexamethylenediamine (1,6-diaminohexane): H₂N-(CH₂)₆-NH₂
(6 carbons total, hence the other "6" in the name)
Name explanation: "Nylon-6,6" indicates that both monomers contain 6 carbon atoms.
How water is eliminated:
The -OH from the acid and one H from the amine combine to form H₂O
The remaining parts join to form an amide link (-CO-NH-)
One H₂O molecule is eliminated for each amide link formed
Properties of Nylon:
Uses:
Other nylon types:
Nylon-6: Made from a single monomer (caprolactam) through self-condensation
Nylon-6,10: Made from a 6-carbon diamine and a 10-carbon diacid
Critical skill: Being able to identify which small molecule is eliminated during condensation polymerization.
For polyesters (acid + alcohol):
Look at what's removed from each monomer:
- From acid: -OH
- From alcohol: -H
- Combine: -OH + H = H₂O (water)
For polyamides (acid + amine):
Look at what's removed from each monomer:
- From acid: -OH
- From amine: -H
- Combine: -OH + H = H₂O (water)
General rule for condensation polymers:
In most condensation polymerizations you'll encounter in HSC Chemistry, the small molecule eliminated is water (H₂O).
How to show this in equations:
When writing condensation polymerization equations, ALWAYS include "+ nH₂O" on the product side, where n is the degree of polymerization.
Example for polyester:
Note: 2nH₂O because each diacid has two -COOH groups, so two water molecules form per repeat unit
Example for polyamide:
Why this matters: Exam questions often ask you to identify the small molecule released or to write balanced equations. Missing the "+ nH₂O" loses marks!