Isomerism
1.0 Isomerism
2.0 Structural Isomerism
2.1 Chain or Nuclear Isomerism
2.2 ${C_5}{H_{12}}$ stands for three chain isomers
2.3 Cyclohexane and methyl cyclopentane are nuclear isomerism
2.4 Position Isomerism
2.5 Functional Isomerism
2.6 Metamerism
2.7 Ring Chain Isomerism
3.0 Tautomerism
3.1 Structural requirement for tautomrism
3.2 Cause of tautomerism
3.3 Keto-enol tautomerim
3.4 Percentage Composition of Tautomeric Mixture
3.5 Triad System containing Nitrogen
3.6 Mechanism of tautomerism
3.7 Stereoisomerism
3.8 Geometrical Isomerism
3.9 Reason of Occurrence of geometrical Isomerism
4.0 Geometrical isomerism in the compounds containing C=N
4.1 Geometrical isomerism in the compounds containing N=N
4.2 Geometrical Isomerism in Cyclic Compounds
4.3 Stability of cis, Trans (or) Geometrical isomers
4.4 Number of Geometrical isomers
4.5 E and Z nomenclature of geometrical isomers
5.0 Optical Isomerism
5.1 Optical Activity
5.2 Asymmetric carbon (or) Chiral Carbon
5.3 Optical isomerism in bromo chloro iodo methane
6.0 Optical isomerism in compounds having more than one chiral carbons
6.1 Elements of symmetry
6.2 Centre of Symmetry
6.3 Stereoisomerism in Tartaric Acid
6.4 Calculation of number of optical isomers
7.0 Optically active compounds having no asymmetric carbon
3.4 Percentage Composition of Tautomeric Mixture
2.2 ${C_5}{H_{12}}$ stands for three chain isomers
2.3 Cyclohexane and methyl cyclopentane are nuclear isomerism
2.4 Position Isomerism
2.5 Functional Isomerism
2.6 Metamerism
2.7 Ring Chain Isomerism
3.2 Cause of tautomerism
3.3 Keto-enol tautomerim
3.4 Percentage Composition of Tautomeric Mixture
3.5 Triad System containing Nitrogen
3.6 Mechanism of tautomerism
3.7 Stereoisomerism
3.8 Geometrical Isomerism
3.9 Reason of Occurrence of geometrical Isomerism
4.2 Geometrical Isomerism in Cyclic Compounds
4.3 Stability of cis, Trans (or) Geometrical isomers
4.4 Number of Geometrical isomers
4.5 E and Z nomenclature of geometrical isomers
5.2 Asymmetric carbon (or) Chiral Carbon
5.3 Optical isomerism in bromo chloro iodo methane
6.2 Centre of Symmetry
6.3 Stereoisomerism in Tartaric Acid
6.4 Calculation of number of optical isomers
Percentage of enol contents of some compounds is given below in the table.
Enol content of some compounds
| Compound | Enol Percentage | Compound | Enol Percentage |
| 0.00025 |
| 31.00 |
| 0.0056 |
| 80.4 |
| 4.8 |
| 89.0 |
| 7.7 |
| 99.99 |
The conversion of a keto form into an enol form is known as enolisation and the enolisation of a compound has been found to depend upon various factors such as structural factor, temperature and nature of solvent. However, the most important is the structural factor (resonance and hydrogen bonding).
(i) Ketonic form predominates in simple monocarbonyl compounds like acetaldehyde, acetone and cyclohexanone. This is due to the greater bond strength of $C{\text{ }} = {\text{ }}O{\text{ }}\{ > C{\text{ }} = {\text{ }}O,{\text{ }}365{\text{ }}kJ/mole)$ present in keto form than the carbon-carbon double bond $\left( {C{\text{ }} = {\text{ }}C,{\text{ }}250{\text{ }}kJ/mole} \right)$ present in enolic form.
(ii) Enolic form predominates in $\beta - $di ketones due to intramolecular hydrogen bonding and resonance. Intramolecular hydrogen bonding stabilizes enol form by $7{\text{ }}kcal/mole$ and resonance stabilizes enol form by $15{\text{ }}kcal/mole.$ Thus enol form is more stable than keto form by $22{\text{ }}kcal/mole$ in $1,3 - diketones.$
