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
3.3 Keto-enol tautomerim
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
In this case the polyvalent atoms are one oxygen and two carbon atoms, e.g. aceto acetic ester, acetyl acetone, benzoyl acetone, acetaldehyde, acetone, phenol etc.
The form containing keto (oxo) group is called keto while that having alkene and –ol functions is called an enol form.
the conversion of a keto form into enol form is known as enolization. It is catalysed by the presence of acid (or) alkali. This dynamic isomerism is shown only by those aldehydes, ketones or esters which have at least one labile $\alpha - $hydrogen atom. For example, benzaldehyde and benzophenone do not have labile $\alpha - $hydrogen, hence these do not show tautomerism.
On other hand, acetophenone contains $\alpha - $ atoms, hence exhibits tautomerism.
Enolization is in the following order:
$C{H_3}COC{H_3} < C{H_3}COC{H_2}COO{C_2}{H_5} < {C_6}{H_5}COC{H_2}COO{C_2}{H_5}$ $ < C{H_3}COC{H_2}CHO < C{H_3}COC{H_2}COC{H_3}$
In compounds whose molecules have two carbonyl groups separated by one $-C{H_2}-$group (called $\beta - $dicarbonyl compounds), the amount of enol present at equilibrium is far higher e.g.
the greater stability of the enol form of $\beta - $dicarbonyl compounds can be attributed to stability gained through resonance stabilization of the conjugated double bonds and (in a cyclic form) through hydrogen bonding.
Percentage of enolic contents of some common compounds in decreasing order is given below:
