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What knowledge about the carbon -carbon bond length in benzene may be obtained from valence bond theory ? |
Answer» Solution :The benzene moleculeis a resonance hybrid of Kekule structures (I) and (II) and contribution of each hybridstructure is 50% i.e., EQUAL.  The single bonds (C-C) and the double bonds (C=C) in structure (I) become double and single bonds respectively in structure (II) . As the two equally stable resonance structures (I) and (II) contribute equally to the hybrid, it may be said that, any two ADJACENT carbon atoms of benzene molecule are linked by a bond INTERMEDIATE between a single and a double bond . so, all the carbon -carbon bonds of benzene are EQUIVALENT and their lengths are equal(1.39 Å) . Again , bond order of each bond isthe same (1.5) . so, it can be said that all carbon -carbon bonds are equal in LENGTH . Bond order = `("Doublebond +Single bond ")/2=(2+1)/2=1.5` |
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