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Contents

I. Structural isomerism
II. Rotational (conformational) isomerism
  Rotational isomerism in open-chained compounds
  Conformational isomerism in cyclic compounds
  Summary and biological importance
III. Geometrical isomerism
  Notation of geometrical isomerism
  Biological importance
IV. Optical isomerism
  Notation of enantiomers
    1. The perspectivic formula and the Cahn-Ingold-Prelog (CIP) system
    2. Projected formula and Fischer's notations
  Compounds with many stereogenic centres
  Racemic and meso compounds
  Formation and separation of racemic mixtures
  Biological importance of chirality
V. Isomerism of other cyclic compounds
  Cyclopropanecarboxylic acids
  Cyclobutanedicarboxylic acids
  Cyclopentanecarboxylic acids
  Cyclohexanehexols
  Disubstituted cyclohexanes
  Decaline

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Preface

Isomers are the compounds with the same qualitative and quantitative composition of elements, therefore their relative molecular weights and general formulas are identical, but their structures - including in the 3D arrangement - are different. The compounds propyl chloride and propane are not isomers, since their qualitative composition of elements are different. The compounds propane and propene are not isomers, although they are built from the same elements, but with different quantitative composition of elements. The compounds propene and cyclohexane are not isomers, although they are built from the same elements, with the same ratio of elements, their relative molecular weights are different. However, the compounds butane and isobutane are isomers, since they have the same general formula, but their 3D arrangement is different. Only one compound or many compounds may have the same general formulas. For example, methane (a linear saturated hydrocarbon) is a single compound without isomer, while pentane has 3 isomers, a linear saturated hydrocarbon with 40 carbons has more than 62 trillion isomers.

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There are versatile types of isomerisms, consequently compounds with identical general formulas may belong to families of compounds quite far from each other. If these families of compounds are closer to each other, then their physical, chemical and biological properties are also similar, but distant relatives may have quite different properties.

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