4. alcohols

specification point: 4.2.1

what are alcohols?

molecules containing the hydroxyl (-OH) group

what are primary alcohols?

the carbon bonded to the hydroxyl group is bonded to one other carbon

what are secondary alcohols?

the carbon bonded to the hydroxyl group is bonded to two other carbons

what are tertiary alcohols?

the carbon bonded to the hydroxyl group is bonded to three other carbons

what are diols?

molecules with 2 hydroxyl groups

why are alcohols less volatile than alkanes + alkenes?

as chain length increases, melting point and boiling point increases, so volatility decreases

why does solubility decrease as chain length increases?

as chain length increases, the non-polar region has a greater influence on solubility than the polar, OH group, so solubility decreases

what is meant by oxidation, in terms of carbon?

a molecule is oxidised when carbon forms a bond with a more electronegative element

what is meant by reduction, in terms of carbon?

a molecule is reduced when carbon forms a bond with a less electronegative element

what are primary alcohols oxidised to?

primary alcohols are oxidised to aldehydes, which are further oxidised to carboxylic acids

what are secondary alcohols oxidised to?

secondary alcohols are oxidised to ketones

why are tertiary alcohols oxidised to?

tertiary alcohols cannot be oxidised

what oxidising agent is used to oxidise alcohols?

\[O\] - acidified potassium dichromate ions

how can alcohols be tested for?

1. primary + secondary alcohols: acidified dichromate ions turn the solution from orange to green

2. tertiary alcohols: solution stays orange

by what process are aldehydes prepared?

distillation

by what process are ketones and carboxylic acids prepared?

reflux

what do alcohols produce (+ conditions) in elimination reactions with water?

alkenes and water

conditions: concentrated acid catalyst, heat

what do alcohols produce (+ conditions) in substitution reactions with sodium halide salts?

haloalkanes, water + salt

conditions: acid catalyst

what test can distinguish primary and secondary alcohols?

• add tollens’ reagent and heat.

• if silver mirror produced, aldehyde, therefore primary alcohol

• if no silver mirror produced, ketone, therefore secondary alcohol

how can fehling’s solution distinguish between primary and secondary alcohols?

fehling’s solution turns red in primary alcohols, but stays blue in secondary alcohols