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Syllabus of Unit 2 :-

Geometrical isomerism
  1. Nomenclature of geometrical isomers (Cis Trans, EZ, Syn Anti systems)
  2. Methods of determination of configuration of geometrical isomers.
  3. Conformational isomerism in Ethane, n-Butane and Cyclohexane.
  4. Stereo isomerism in biphenyl compounds (Atropisomerism) and conditions for optical activity.
  5. Stereospecific and stereo selective reactions.

1. Geometrical isomerism

Geometrical isomerism could be a kind of stereoisomerism having the identical formula and same structure but differ within the relative arrangement of atoms. Geometrical Isomerism, which arises commonly in heteroleptic complexes. this sort of isomerism arises thanks to the various possible geometric arrangements for the ligand.

The geometrical isomerism arises when atoms or groups are arranged differently in space thanks to restricted rotation of a bond or bonds in an exceedingly molecule.

2. Stereo isomerism

Stereoisomerism, or spatial isomerism, could be a sort of isomerism during which molecules have the identical formula and sequence of bonded atoms (constitution), but differ within the three-dimensional orientations of their atoms in space. This contrasts with structural isomers, which share the identical chemical formula, but the bond connections or their order differs. By definition, molecules that are stereoisomers of every other represent the identical structural isomer.

3. Conformational isomerism

In chemistry, conformational isomerism may be a kind of stereoisomerism within which the isomers may be interconverted just by rotations about formally single bonds (refer to work on single bond rotation). While any two arrangements of atoms in an exceedingly molecule that differ by rotation about single bonds will be observed as different conformations, conformations that correspond to local minima on the mechanical energy surface are specifically called conformational isomers or conformers.

Conformations that correspond to local maxima on the energy surface are the transition states between the local-minimum conformational isomers. Rotations about single bonds involve overcoming a rotational energy barrier to interconvert one conformer to a different.

If the energy barrier is low, there's free rotation and a sample of the compound exists as a rapidly equilibrating mixture of multiple conformers; if the energy barrier is high enough then there's restricted rotation, a molecule may exist for a comparatively while period as a stable rotational isomer or rotamer (an isomer arising from hindered single-bond rotation). When the duration for interconversion is long enough for isolation of individual rotamers (usually arbitrarily defined as a half-life of interconversion of 1000 seconds or longer), the isomers are termed atropisomers (see: atropisomerism). The ring-flip of substituted cyclohexanes constitutes another common sort of conformational isomerism.