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7. Fundamental Principles of Organic Chemistry eLearn.Punjab

(iv) Metamerism

This type of isomerism arises due to the unequal distribution
of carbon atoms on either side of the functional group. Such
compounds belong to the same homologous series. For
example, diethyl ether and methyl n-propyl ether are metamers.

CH3 − CH2 − O − CH2 − CH3 CH3 − O − CH2 − CH2 − CH3
Diethyl ether Methyl n-propyl ether

For a ketonic compound having the molecular formula C5H10O, the following
two metamers are possible.

(v) Tautomerism

This type of isomerism arises due to shifting of proton from one atom to other
in the same molecule.

(2) Cis-trans Isomerism or Geometric Isomersim

Two carbon atoms joined by a single bond are capable of free rotation about
it. However, when two carbon atoms are joined by a double bond, they
cannot rotate freely. As a result, the relative positions of the various groups
attached to these carbon atoms get fixed and gives rise to cis- trans isomers.

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