showing hyperconjugation in ethyl cation This type of overlap stabilises the carbocation because electron density from the adjacent σ bond helps in dispersing the positive charge. In general, greater the number of alkyl groups attached to a positively charged carbon atom, the greater is the hyperconjugation interaction and stabilisation of the cation. Thus, we have the following relative stability of carbocations : Hyperconjugation is also possible in alkenes and alkylarenes. D e l o c a l i s a t i o n o f e l e c t r o n s b y hyperconjugation in the case of alkene can be depicted as in Fig.
. (b). Problem . Explain why (CH ) C + is more stable than CH C + H and C + H is the least stable cation.
Hyperconjugation interaction in (CH ) C + is greater than in CH C + H as the (CH ) C + has nine C-H bonds. In C + H , vacant p orbital is perpendicular to the plane in which C-H bonds lie; hence cannot overlap with it. Thus, C + H lacks hyperconjugative stability. .
. Types of Organic Reactions and Mechanisms Organic reactions can be classified into the following categories: (i) Substitution reactions (ii) Addition reactions (iii) Elimination reactions (iv) Rearrangement reactions You will be studying these reactions in Unit and later in class XII. . Methods of Purification of Organic Compounds Once an organic compound is extracted from a natural source or synthesised in the laboratory, it is essential to purify it.
Various methods used for the purification of organic compounds are based on the nature of the compound and the impurity present in it. The common techniques used for purification are as follows : (i) Sublimation (ii) Crystallisation (iii) Distillation (iv) Differential extraction and (v) Chromatography Finally, the purity of a compound is ascertained by determining its melting or boiling point. Most of the pure compounds have sharp melting points and boiling points. New methods of checking