Naming and physical properties of alcohols.

Naming alcohols

Alcohols are an homologous series

with the general formula; CnH2n+1OH

A suffix, -ol, is used to indicate the presence of an hydroxyl group.

Eg; CH3CH(OH)CH3 propan- 2-ol

Classifying alcohols

Look at the number of alkyl groups attatched to the carbon which bears the hydroxyl group.

Primary alcohols

Have ONE alkyl group on the carbon that bears the hydroxyl group.

R

Eg; CH3CH2OH

Secondary alcohols

Have TWO alkyl groups on the carbon with the hydroxyl group.

R

R(CH3)2CHOH

Tertiary alcohols

Have THREE alkyl groups on the carbon with the hydroxyl group.

RR

R

(CH3)3COH

Name the following alcohols, stating whether they are primary, secondary or

tertiary;

• CH3OH

• CH3CH2CH(OH)CH

3

• (CH3)2(C2H5)COH

• CH3C(CH3)2CH2OH

• Methanol (1o)• Butan 2 ol (2O)• 2 methyl butan 2

ol (3O)• 2,2 dimethyl

propan 1 ol (1o)

Draw out the structures of the following alcohols, stating whether they are

primary, secondary or tertiary;

• Heptan 1 ol• 2,2 dimethyl

hexan 3 ol• 4 methyl octan 4

ol

• CH3(CH2)5CH2OH

• (1o)• (CH3)3 CH(OH)

(CH2)2CH3

• (2O)• CH3(CH2)2CH(OH)

(CH2)2 CH3

• (3O)

Boiling points

Alkane BP oC Alcohol BP oC

methane -163.4 methanol 65

ethane -88.5 ethanol 78

propane -42 propanol 98

butane -0.4 butanol 117

pentane 36.2 pentanol 138

Plot BP against Mr and comment on the trends.

BPs of alkanes and alcohols compared

0

100

200

300

400

500

600

700

800

900

C1 C2 C3 C4 C5 C6

Number of carbons

BP

(K) alcohol

alkane

Alcohols have much higher BPs than those of the corresponding alkane.

The intermolecular bonds in alkanes are only weak van der Waals.

But in alcohols there are much stronger hydrogen bonds.

BPs of alcohols compared with those of alkanes.

Solubility of alcohols

Alcohols are miscible in

water.

δ-

δ+

δ-

δ+

δ-δ+

δ+ δ+The hydroxyl group can hydrogen bond with water.

Solubility decreases with chain length.

But hydrocarbon chains can only make van der Waals interactions.

The hydroxyl group can hydrogen bond…