Dictionary of Chemistry [6th Ed.]

have different positions of groups

with respect to a double bond or ring

or central atom (see illustration).

Octahedral complexes can display

cis-trans isomerism if they have for-

mulae of the type MX 2 Y 4. Octahedral

complexes with formulae of the type

MX 3 Y 3 can display a different type of

isomerism. If the three X ligands are

in a plane that includes the metal

atom and the three Y ligands are in a

different plane at right angles, then

isomerism 296

i

1-chloropropane

HCCCCI

H

H

H

H

H

H

HCCCH

H

H

CI

H

H

H

2-chloropropane

structural isomers in which the functional group has different positions

methoxymethane ethanol

structural isomers in which the functional groups are different

trans-but-2-ene cis-but-2-ene

cis–trans isomers in which the groups are distributed on a double bond

cis–trans isomers in a square-planar complex

HCOCH

H

H

H

H

HCCOH

H

H

H

H

HCH 3

C C

CH 3 H

CH 3

C C

H H

CH 3

keto form enol form

CC

O

C C

OH

CI I

I CI

Pt

ICI

I CI

Pt

keto–enol tautomerism

Isomerism