Alcohols

Lesson

Part 1 — compounds with an –OH group on an sp³ carbon: names, preparation and physical properties.

In this lesson you will

Classify and name alcohols and compare 1°, 2° and 3° alcohols
Write equations to prepare alcohols from alkenes, Grignard reagents, alkyl halides, carbonyl compounds and primary amines
Outline the manufacture of methanol and ethanol
Explain the boiling points and solubility of alcohols

Table of familiar alcohols
Alcohol	Where you meet it
Ethanol	Hand sanitiser, fuel blended with petrol
Methanol	Solvent; poisonous
Propan-2-ol	Rubbing alcohol
Ethane-1,2-diol	Antifreeze in car radiators
Propane-1,2,3-triol (glycerol)	Soaps, cosmetics

Concept

Classification and general formula

By the number of –OH groups: monohydric (CₙH₂ₙ₊₁OH), dihydric (glycols), trihydric (glycerol). Monohydric alcohols are primary, secondary or tertiary according to the carbon bearing –OH.

Table classifying alcohols
Class	Group	Example
Primary (1°)	–CH₂OH	Butan-1-ol, CH₃CH₂CH₂CH₂OH
Secondary (2°)	CHOH	Butan-2-ol, CH₃CH₂CH(OH)CH₃
Tertiary (3°)	≡C–OH	2-Methylpropan-2-ol, (CH₃)₃COH
Dihydric	Two –OH	Ethane-1,2-diol
Trihydric	Three –OH	Propane-1,2,3-triol

Concept

Nomenclature

IUPAC: longest chain containing the C–OH; replace -e of the alkane by -ol; lowest locant to –OH. Diols and triols keep the -e (ethane-1,2-diol). Common names: alkyl + alcohol.

Table of common and IUPAC names of alcohols
Structure	Common name	IUPAC name
CH₃OH	Methyl alcohol (wood spirit)	Methanol
CH₃CH₂CH₂OH	n-Propyl alcohol	Propan-1-ol
(CH₃)₂CHCH₂OH	Isobutyl alcohol	2-Methylpropan-1-ol
CH₃CH₂CH(OH)CH₃	sec-Butyl alcohol	Butan-2-ol
(CH₃)₃COH	tert-Butyl alcohol	2-Methylpropan-2-ol
HOCH₂CH₂OH	Ethylene glycol	Ethane-1,2-diol

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