02-STEREOCHEMISTRY-02: Beginning

DR. KARTIK KUMAR NANDI

ASSOCIATE PROFESSOR OF CHEMISTRY

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DEPARTMENT OF CHEMISTRY

BRAHMANANDA KESHAB CHANDRA COLLEGE

KOLKATA – 700108

E-Mail: kknandi@yahoo.com

BOOKS OF STEREOCHEMISTRY:

1. Basic Stereochemistry of Organic Molecules: Subrata Sengupta
2. Stereochemistry of Organic Compounds: Principles & Applications - D. Nasipuri

3.1 CONCEPT OF ISOMERISM

• Berzelius coined the term isomerism (Greek: isos = equal; meros = part) to describe the relationship between two clearly different compounds having the same elemental composition. Such pairs of compounds differ in their physical and chemical properties and are called isomers. For example,
• Ethyl alcohol (CH₃CH₂OH) and
• Dimethyl ether (CH₃OCH₃) are isomers.

3.2 TYPES OF ISOMERISM

I. Chain/Skeletal/Nuclear Isomerism

• These have same molecular formula but different arrangement of carbon chain within the molecule.

II. Position Isomerism

These have same carbon skeleton but differ in the position of attached atoms or groups or in position of multiple (double or triple) bonds.

III. Functional Isomerism

• These have same molecular formula but different functional groups.

IV. Metamerism

• These have different number of carbon atoms (or alkyl groups) on either side of a bifunctional group (i.e., -O- , -S-, -NH-, -CO- etc.). Metamerism is shown by members of the same family, i.e., same functional groups.

V. Tautomerism

• Structural or constitutional isomers existing in easy and rapid equilibrium by migration of an atom or group are tautomers (keto-enol tautomerism).

Review of Isomerism

• Isomers – Compounds that have the same molecular formula but do not have identical structures.
• Constitutional Isomers – differ in the way their atoms are connected.
• Stereoisomers – differ in the way their atoms are arrange in space.

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