Alcohols Introduction and Reactions

Flashcards covering the classification, naming, physical properties, production, and chemical reactions of alcohols based on the provided lecture notes.

General formula of an alcohol

$C_nH_{2n+1}OH$ (often shortened to $ROH$).

Hydroxyl group

The $-OH$ functional group attached to a hydrocarbon chain.

Primary ($1^{\circ}$) alcohol

An alcohol where the carbon atom bonded to the $-OH$ group is attached to one $R$ group (and therefore two hydrogen atoms).

Secondary ($2^{\circ}$) alcohol

An alcohol where the $-OH$ group is attached to a carbon atom with two $R$ groups (and therefore one hydrogen atom).

Tertiary ($3^{\circ}$) alcohol

An alcohol where the carbon atom bonded to the $-OH$ group is attached to three $R$ groups (and therefore no hydrogen atoms).

Ethanol health effects

A nervous system depressant that interferes with nerve impulse transmission; in large amounts, it leads to loss of balance, impaired vision, and can be fatal.

$C-O-H$ bond angle

Approximately $105^{\circ}$ (or $104.5^{\circ}$) because the presence of two lone pairs on the oxygen atom repels bonding pairs, squeezing the angle down from the perfect tetrahedral $109.5^{\circ}$.

Glycerol

The common name for propane-1,2,3-triol, often obtained from fats and oils.

Ethane-1,2-diol

The main ingredient in most antifreezes used in motor vehicle cooling systems.

Alcohol solubility

Short-chain alcohols are soluble in water due to hydrogen bonding; solubility decreases as the non-polar hydrocarbon chain lengthens and dominates.

Hydration of ethene

An industrial method of producing ethanol by reacting ethene (from cracked crude oil) with steam using a phosphoric acid catalyst.

Fermentation of ethanol

The process where carbohydrates from plants are broken down into sugars and converted into ethanol by yeast enzymes under anaerobic conditions at about $35\,^{\circ}C$.

Biofuel

A fuel derived or produced from renewable biological sources.

Carbon-neutral fuel

A fuel, such as ethanol from fermentation, where the $CO_2$ released during combustion and production is balanced by the $CO_2$ absorbed by the plants during photosynthesis.

Methylated spirits

Ethanol with a small amount of poisonous methanol and a purple dye added to make it undrinkable and tax-free for use as a fuel.

Elimination reaction (Dehydration)

A reaction where a water molecule is removed from an alcohol (using an $-OH$ group and a hydrogen from an adjacent carbon) to form an alkene.

Oxidising agent for alcohols

Acidified potassium dichromate($VI$), which changes colour from orange ($Cr(VI)$ ions) to green ($Cr(III)$ ions) upon reduction.

Oxidation of primary alcohols

Oxidised to aldehydes ($RCHO$) via distillation or further oxidised to carboxylic acids ($RCOOH$) via reflux.

Oxidation of secondary alcohols

Oxidised to ketones ($R_2CO$) which are not easily oxidised further.

Oxidation of tertiary alcohols

Not easily oxidised because the reaction would require breaking a stable $C-C$ bond.

Reflux

A laboratory technique where vapour condenses and drips back into the reaction flask, allowing prolonged heating to ensure complete oxidation.

Tollens' reagent test

A test using silver nitrate in aqueous ammonia that forms a 'silver mirror' when warmed with an aldehyde, but shows no reaction with ketones.

Fehling's test

A test using blue copper($II$) complex ions that form a brick red precipitate of copper($I$) oxide when warmed with an aldehyde.