AS level chemistry organic

Only type of amine group we need to learn for AS level

primary amine

Describe primary amine synthesis

Describe addition polymerisation

Addition polymers are (very) large molecules made up of repeating units, bonded together over and over again. Repeating units are formed from small molecules called monomers.

Properties of addition polymer

Addition polymers are chemically inert because strong C–C and C–H bonds make addition polymers very unreactive.

They are also Non-biodegradable: These materials are not broken down naturally, causing long-term environmental issues. The strength and stability of the carbon chain makes these materials resistant to biological and chemical degradation.

Environmental issues of addition polymer

• Disposal: Polyalkenes accumulate in landfill due to their resistance to decay (non-biodegradable).

• Combustion products:

  • Burning poly(chloroethene) (PVC) releases toxic hydrogen chloride (HCl) gas.

  • Incineration can contribute to air pollution and acid rain if not properly managed.

As a result, care must be taken when disposing of polymers, particularly halogenated ones like PVC, due to the risk of toxic emissions.

List back and describe all the tests for Alkene, alcohol, aldehyde, and ketone

List all mechanism in AS level chemistry

1. Free-radical substitution

2. Electrophilic addition

3. Nucleophilic addition

4. Nucleophilic substitution

Describe synthesis of carboxylic acid (using nitriles) and there’re 2 alternatives

1. Dilute acid —→ acidification

2. Dilute alkali —→ acidification

Acid Hydrolysis of ester (carboxylic acid synthesis)

Reagents: dilute H2SO4 or HCl

Conditions: heat under reflux

Alkali Hydrolysis of ester (carboxylic acid synthesis)

Reagents: Dilute NaOH

Conditions: heat under reflux, follow by acidification

Describe carboxylic acid Redox Reaction with Reactive Metals (carboxylate salt synthesis)

Describe carboxylic acid Neutralisation with Alkalis

Describe carboxylic acid Reaction with Carbonates

Esterification of carboxylic acid (Ester synthesis)

Describe synthesis reaction of aldehyde using primary alcohol

Describe synthesis reaction of ketone using secondary alcohol

Describe reaction of aldehyde/ketone to form hydroxynitrile

describe nucleophilic addition mechanism (of HCN in forming hydroxynitriles from carbonyl group)

Describe test with 2,4-DNPH

Describe Fehling’s test

describe Tollens’ Silver Mirror Test

Describe iodoform test

Alcohol

organic compounds that contain a carbon atom bonded to a hydroxy, OH group

Reduction of aldehydes/ ketones

(alcohol synthesis)

Why reduction using LiAlH₄ need to be in dry ether?

LiAlH₄ is a more powerful reducing agent than NaBH₄, because of this if LiAlH₄ is used no water can be present and the reaction must be carried out in dry ether.

What NaBH₄ and LiAlH₄ stand for?

NaBH₄ : sodium borohydride

LiAlH₄ : Lithium aluminum hydride

Reduction of Carboxylic Acids

(alcohol synthesis)

Hydrolysis of Esters (there are two alternative by-products)

(Alcohol synthesis)

Alcohol combustion

Alcohols (especially shorter chain alcohols) burn cleanly to form CO₂ and water making them useful as fuels.

Example CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O

Alcohol reacts with sodium (Alkoxide synthesis)

Different types of alcohol

Primary alcohol oxidation (aldehyde synthesis)

Primary alcohols oxidise first to aldehydes, then to carboxylic acids

reagent: K₂Cr₂O₇/ H⁺

condition: distillation + heat

Observation when alcohol oxidized to form aldehyde / carboxylic acid

Observation: Orange Cr₂O₇²⁻ (dichromate) turns green (Cr³⁺ formed)

Route for oxidation of primary alcohol

Alcohol ——[O] —→ Aldehyde ——-[O]——> Carboxylic acid

Why need distillation during the oxidation of alcohol to form aldehyde

to remove aldehyde before it can further oxidised into carboxylic acid (this will create a mixture)

Primary alcohol oxidation (carboxylic acid synthesis)

reagent: K₂Cr₂O₇/ H⁺ OR (KMnO₄/H⁺ , quite strong=> result to carboxylic acid directly)

condition: heat in reflux

Oxidation for secondary alcohol (ketone synthesis)

reagent: K₂Cr₂O₇/ H⁺

condition: heat under reflux

Observation for secondary alcohol oxidation (ketone synthesis)

Orange Cr₂O₇²⁻ (dichromate) turns green (Cr³⁺ formed).

Why ketone/ tertiary alcohol can’t oxidise further

Because there are no more hydrogen bonded to the carbon that bonded with the oxygen

Esterification of alcohol

Reagents: conc.H2SO4 , carboxylic acid

Condition: heat under reflux

What iodoform test used for?

To test the presence of CH₃CH(OH)–R Group

How iodoform test find the presence of CH3CH(OH)- group

Products: tri-iodomethane, RCO₂^- (by-products: iodide, water)

Compare acidity of alcohol with water

Alcohols are much weaker acids than water. They are less able to lose H⁺ ions.

This is because the alkoxide ion (RO⁻) formed after losing a H⁺ ion is less stable than the hydroxide ion (OH⁻) formed from water. This is due to the electron-donating nature of the alkyl group, which increases the electron density on the negatively charged oxygen, making it less stable and less likely to form. In contrast, the hydroxide ion is more stable, so water more readily donates a proton, making it a stronger acid than alcohols.

Halogenoalkane

molecules contain a halogen (F, Cl, Br, I) bonded to a carbon

Alcohols nucleophilic substitution (halogenoalkane synthesis)

Types of halogenoalkane

Primary	halogen bonded to C with 1 alkyl group
Secondary	bonded to C with 2 alkyl groups
Tertiary	bonded to C with 3 alkyl groups

Halogenoalkane nucleophilic substitution with NaOH

• Alcohol synthesis

• NaOH must be aqueous

Halogenoalkane nucleophilic substitution with KCN

• nitrile synthesis

Halogenoalkane nucleophilic substitution with NH₃

Test for identify halide in halogenoalkane (reagents, conditions, positive results for each halides Cl, Br, I)

Nucleophilic substitution reactions

when a nucleophile (electron pair donor) replaces a leaving group (a halide ion) in a halogenoalkane.

two possible mechanisms of nucleophilic substitution

SN1 and SN2

Describe SN2 mechanism

• Occurs in one step (both reactants are involved in the same step).

• The nucleophile attacks the carbon at the same time as the leaving group (halide) departs.

• A transition state is formed with partial bonds — both the nucleophile and the leaving group are briefly attached.

Which types of halogenoalkane favour SN2 mechanism

Favoured by primary halogenoalkanes (sometime secondary), because of less steric hindrance (blocked by carbon alkyl groups) allowing the nucleophile to easily from the back

Describe SN1 mechanism

• Occurs in two steps.

• 1. The halide leaves first, forming a carbocation (slow step – rate-determining).

• 2. The nucleophile then attacks the positively charged carbon (carbocation intermediate)

• 3. New bond formed between the C and OH.

Which types of halogenoalkane favour SN1 mechanism

Favoured by tertiary halogenoalkanes, where the carbocation is stabilised by alkyl groups via the positive inductive effect (electron-donating effect of surrounding alkyl groups).

Order of reactivity (and rate of reaction) of halogenoalkane and explain why

Order of reactivity (fastest→slowest): Iodoalkanes > Bromoalkanes > Chloroalkanes > Fluoroalkanes

• stronger bond strength → need more energy to break→ low reactivity

order of bond strength (strongest→weakest): C-F > C-Cl > C-Br > C-I

Alkane

• Alkanes are saturated hydrocarbons, meaning they contain only single C–C and C–H bonds.

• General formula: C_nH_2n+2

• They are non-polar and insoluble in water.

Why alkanes are generally unreactive

• C–C and C–H bonds are strong and non-polar.

• Molecules have low polarity, so they don't attract polar reagents.

[Conditions] hydrogenation/ reduction of alkene [alkane synthesis]

Catalyst: Ni or Pt

Temp: 150 - 200 Celcius

Why need cracking

Cracking breaks large hydrocarbon molecules into smaller, more useful ones.

Shorter chain hydrocarbons are in greater demand for use of fuels (they ignite more easily and are less likely to undergo incomplete combustion).

[conditions] catalytic cracking (alkane and alkene synthesis)

• alkane —> alkene + (shorter) alkane

• Catalyst: Al₂O₃ or zeolite

• Heat: 450–750°C

Complete combustion [reactions of alkane]

occurs when there is enough oxygen present and carbon can be fully oxidised

Alkane + O₂ ——→ CO₂ + H₂O

Incomplete combustion [reactions of alkane]

occurs when there is limited oxygen present and carbon can’t be fully oxidised, meaning carbon monoxide (CO) or carbon (soot) gets formed as a product (and water).

• CH₄ + 1.5O₂ → CO + 2H₂O

• CH₄ + O₂ → C + 2H₂O

Free radical substitution

Alkanes react with halogens (Cl₂, Br₂) under UV light to form halogenoalkanes by free radical substitution.

mechanism of free radical substitution

• Step 1: Initiation
  UV light provides energy to break the Cl–Cl bond by homolytic fission. Each chlorine atom ends up with an unpaired electron (•), making it a radical.

• Step 2: Propagation
  Radicals react to form new radicals in a chain reaction. Chlorine radical reacts with methane, forming a methyl radical. Methyl radical reacts with Cl₂, forming chloromethane and a new Cl• radical.

• Step 3: Termination
  Radicals combine to form stable (non-radical) molecules, stopping the reaction.

Which harmful molecules formed from Internal Combustion Engines

CO, NO and NO₂, C, unburnt hydrocarbon

Harmful effects of CO, oxides of nitrogen, C, and unburnt hydrocarbon

• Carbon Monoxide, CO
  binds to haemoglobin and is toxic

• Nitrogen Oxides, NO and NO₂
  formed when N₂ and O₂ react at high temps; causes acid rain and smog

• Carbon, C (soot)
  causes respiratory problems

• Unburnt hydrocarbons
  contribute to photochemical smog

How harmful products of internal combustion engine removed

Describe elemination of HX from Halogenoalkanes [alkene synthesis]

Describe dehydration of alcohol [alkene synthesis]

Alkene electrophilic addition

Alkenes react with electrophiles in electrophilic addition reactions. The high electron density within a carbon-carbon double bond attracts electrophiles.

Alkene electrophilic addition of hydrogen

Alkane synthesis

Alkene electrophilic addition of steam

Alcohol synthesis

Alkene electrophilic addition of hydrogen halide (HX_(g))

Halogenoalkane synthesis

Alkene electrophilic addition of halogen (X₂)

Halogenoalkane synthesis

Alkene oxidation with Cold Dilute KMnO₄ (Potassium permanganate)

Diol synthesis

Alkene oxidation with Hot Conc. KMnO₄ (Potassium permanganate)

Cleavage (in chemistry)

splitting or breaking of bonds between ions, atoms, molecules

How many alternative products are there in alkene oxidation with Hot Conc. KMnO₄

3 product pathways (depend on the cleavage of the bond in alkene)

Describe addition polymerisation

Describe test for alkene (Bromine water)

Mechanism of electrophilic addition

Draw electrophilic addition mechanism for Bromine + Ethene

Draw electrophilic addition mechanism for HBr + Ethene

Major and minor product

Major : products that formed the most

Minor : products that formed less

Alkyl groups

A chain of carbon backbone (CH3, C2H5, C3H7…)

Markovnikov’s rule

Major product will be the one where H from HX bonds to carbon in C=C that is bonded to the most hydrogens

Carbocation

a carbon positively charged ion

Types of carbocation and their order of stability

Inductive effect

When alkyl groups gives electron density to the carbocation in order to stabilize it. More alkyl groups bonded, more stable carbocation.

Use inductive effect to explain Markovnikov’s rule

• HX get polarised

• Hydrogen (+) bonded with less stable carbon (C=C bond)

• X (or any other species) bonded with more stable carbocation

a group of atoms that determine a molecule’s physical and chemical properties

A family of compounds with the same functional group and general formula. Also, each successive members differ by a unit of -CH₂-

[and its general formula]

C_nH_2n+1X where X is a halide