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49. Explain hyperconjugation effect or No-bond resonance, Ans. Hyperconjugation describes the orbital interactions between the 2-systems and the adjacent, , o-bonds of the substituent group(s) in organic, , compound. This effect arises due to partial overlap of the, empty p-orbital of a positively charged carbon atom with . ° 3 CC 3H}, ‘, the adjacent o-orbital of sp” — s (a C—H bond) of the ‘P eee. “4, + /] ex, alkyl group. For example, let us consider CH,—CH, YW H, Se, (ethyl cation) in which the positively charged carbon H, , atom has an empty p-orbital. One of the C—H bonds of oe, , the methyl group can align in the plane of this empty p-orbital and the electron constituting the, , C—H bond in plane with this p-orbital can then be delocalised into the empty p-orbital., , Such interaction between C—H a bond and empty p-orbital of an adjacent positively charged, carbon atom is referred to as hyperconjugation. This type of overlap stabilises the cation because, electron density from the adjacent 0 bond helps in dispersing the positive charge. It should be, noted that greater the number of alkyl groups attached to a positively charged carbon atoms,, greater is the hyperconjugation interaction and the stabilisation of the cation. The order of, , decreasing stabilities of carbocation is, + i, , + +, (CH,),C > (CH,),CH > CH,—CH, > CH,, , 2 Fe ge mentee oo