Question

what is meant by isomerism​

Answer 1

isomerism, the existence of molecules that have the same numbers of the same kinds of atoms (and hence the same formula) but differ in chemical and physical properties. ... Timing and energy are also factors in isomerism.
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Answer 2

Isomerism:

   Isomerism, the existence of molecules that have the same number of the same kinds of atoms but differs in chemical and physical properties. Timing and energy are also factors in isomerism.

Molecules are mobile entities, undergoing all sorts of rotational motions that change their shapes, and those motions requires energy. Thus, some molecules can be the same on one timescale or set of energy conditions but different, or isomeric, on other.

Finally, an isomer must be an energy minimum, it must lie in an energy well. eg: 1-pentene and 2-pentene are isomers.

Types:

 There are two primary types of isomerism, which can be further categorized into different subtypes:

• Structural isomerism
• Stereoisomerism

Structural isomerism:

  Structural isomerism is commonly referred to as constitutional isomerism. The functional groups and the atoms in the molecules of these isomers are linked in different ways. The different types of structural isomerism are discussed:

• Chain isomerism
• Position isomerism
• Functional isomerism
• Metamerism
• Tautomerism
• Ring-chain isomerism

Stereoisomerism:

 This types of isomerism arises in compounds having the same chemical formula but different orientations of the atoms belonging to the molecules in the three-dimensional space.

• Geometric isomerism
• Optical isomerism.