Alcohols

Alcohols general formula

CnH2n+1OH

Alcohols functional group

OH

Alcohols suffix

-ol

Primary alcohols

Contain one R group attached to the carbon with the OH group

Secondary alcohols

Contain 2 R groups attached to the carbon with OH group attached to it

Tertiary alcohols

Contains 3 R groups attached to the carbon with OH group attached to it

Alcohols polarity

Alcohols are polar as the OH group is more electronegative than the carbon it’s attached to and the OH group itself is polar as the oxygen atom is more electronegative than the hydrogen atom

Result of alcohols polarity

The delta positive charge on the hydrogen atom in the OH group can attract lone pairs on oxygen molecules from a molecule like water forming hydrogen bonds.This makes alcohols soluble but also have a low volatility

trend in solubility of alcohols

The solubility of alcohols decreases the longer the alcohol chain becomes as most of the molecule is then a non-polar carbon chain so there’s less attraction for the polar water molecules

Boiling points of alcohols

Alcohols can undergo hydrogen bonding which causes a relatively high boiling point as lots of energy is required to break these bonds but this also causes alcohols to have a low volatility

Elimination reactions of alcohols

These produce alkenes by removing the H20 from the alcohol. These reactions require a concentrated acid catalyst such as concentrated H2SO4 and the mixture to be heated.

Why can elimination reactions form E/Z isomers?

The H20 molecule removed is formed from the OH group and a hydrogen atom form the carbon adjacent from the one attached to the OH so there’s two possible alkene products.

Substitution reactions of alcohols

Alcohols will react with compounds containing halide ions producing a haloalkane via the OH being replaced by a halide. This reaction requires an acid catalyst such as H2SO4

General equation of alcohols substitution reactions

R-OH + NaX —→ R-X + Na+ + H20

Oxidising alcohols

This can be done by burning the alcohol resulting in CO2 and H20 being formed or an oxidising agent can be used

Oxidising agent of alcohols

Potassium dichromate (VI) - K2Cr2O7 or acidified potassium dichromate (VI) - K2Cr2O7/H2SO4

Oxidation of primary alcohols

These can be oxidised to aldehydes then carboxylic acids. This results a colour change from orange to green due to the Cr2O7 2- is reduced to a Cr 3+ (chromium ion)

Aldehydes

A type of carbonyl compound with a functional group of C=O. This functional group is always attached to carbon 1

Aldehydes general formula

CnH2n+1CHO

Aldehydes suffix

-al

Oxidation of secondary alcohols

These can be oxidised to ketones

Ketones

These are a type of carbonyl compound with a functional group of C=O. This group is found on carbons with two alkyl groups attached to it.

Ketones suffix

-one

General equation for the oxidation of primary alcohols

R-CH2-OH —→ [0] R-C=O-H —> [0] R-C=O-OH

Reaction conditions for aldehyde

Primary alcohol have to be oxidised under distillation for them to be the only product also results in the production of water

Reaction conditions for carboxylic acid

You have to vigorously oxidise the alcohol, use excess oxidising agent and beating the reaction under reflux

Carboxylic acids

Have the functional group COOH which is always in the end of the carbon chain

Carboxylic acid suffix

-oic acid

Oxidation of tertiary alcohols

Can only be oxidised by being burned due to the lack of a hydrogen atom on the carbon with the hydroxyl group