Dictionary of Chemistry [6th Ed.]

biosynthesized from amino acids and

classiÜed according to some struc-

tural feature. A simple classiÜcation

is into:

the pyridine group (e.g. coniine, nico-

tine)

the tropine group (e.g. atropine, co-

caine)

the quinoline group (e.g. quinine,

strychnine, brucine)

the isoquinoline group (e.g. mor-

phine, codeine)

the phenylethylamine group (e.g.

methamphetamine, mescaline,

ephedrine)

the indole group (e.g. tryptamine, ly-

sergic acid)

the purine group (e.g. caffeine, theo-

bromine, theophylline)

alkanalAn aliphatic aldehyde.

alkanes(parafÜns)Saturated hy-

drocarbons with the general formula

CnH 2 n+2. In systematic chemical

nomenclature alkane names end in

the sufÜx -ane. They form a *homolo-

gous series (the alkane series)

methane (CH 4 ), ethane (C 2 H 6 ),

propane (C 3 H 8 ), butane (C 4 H 10 ), pen-

tane (C 5 H 12 ), etc. The lower members

of the series are gases; the high-mo-

lecular weight alkanes are waxy

solids. Alkanes are present in natural

gas and petroleum. They can be

made by heating the sodium salt of a

carboxylic acid with soda lime:

RCOO–Na++ Na+OH–→Na 2 CO 3 +

RH

Other methods include the *Wurtz

reaction and *Kolbe’s method. Gener-

ally the alkanes are fairly unreactive.

They form haloalkanes with halo-

gens when irradiated with ultraviolet

radiation.

A

• Information about IUPAC nomenclature


• Further details about IUPAC
  nomenclature

alkanolAn aliphatic alcohol.

alkenes(oleÜnes; oleÜns)Unsatu-

rated hydrocarbons that contain one

or more double carbon–carbon bonds

in their molecules. In systematic

chemical nomenclature alkene

names end in the sufÜx -ene. Alkenes

that have only one double bond form

a homologous series (the alkene se-

ries) starting ethene (ethylene),

CH 2 :CH 2 , propene, CH 3 CH:CH 2 , etc.

The general formula is CnH 2 n. Higher

members of the series show iso-

merism depending on position of the

double bond; for example, butene

(C 4 H 8 ) has two isomers, which are (1)

but-1-ene (C 2 H 5 CH:CH 2 ) and (2) but-2-

ene (CH 3 CH:CHCH 3 ): see formulae.

Alkenes can be made by dehydration

of alcohols (passing the vapour over

hot pumice):

RCH 2 CH 2 OH – H 2 O →RCH:CH 2

alkanal 20

a

2 CH

C

H

C

H 2

CH 3

3 CH

C

H

C

H

CH 3

but-1-ene

but-2-ene

Alkenes

An alternative method is the removal

of a hydrogen atom and halogen

atom from a haloalkane by potas-

sium hydroxide in hot alcoholic solu-

tion:

RCH 2 CH 2 Cl + KOH →KCl + H 2 O +

RCH:CH 2

Alkenes typically undergo *addi-

tion reactions to the double bond.

They can be tested for by the *Baeyer

test. See also hydrogenation; oxo

process; ozonolysis; ziegler

process.

A

• Information about IUPAC nomenclature

alkoxidesCompounds formed by