T he inductive effects of su b stitu e n t groups on th e 77-electrons o f aro m atic hy d ro carb o n s are estim ated q u a n tita tiv e ly from electronic spectroscopic d a ta . Two m eth o d s are used to ev alu ate th e param eters. T he first is based on th e first-order changes in th e energy of th e first tra n sitio n of azulene on m o n o -su b stitu tio n a n d th e second is based on th e second-order changes in th e energy o f th e first tra n sitio n of benzene on poly su b stitu

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... io n . T he agreem ent b etw een th e values o b tain ed b y th e tw o m ethods is good except for accep to r su b stitu e n ts for w hich th e values o b tain ed b y th e first m eth o d are considerably sm aller th a n those o b tain ed by th e second. U sing these values of th e in d u ctiv e p a ra m e te r we h av e calcu lated th e sp littin g of th e ground s ta te of th e benzene negative ion b ro u g h t a b o u t b y su b stitu e n ts; an d th e relationship of th is sp littin g to th e electron spin resonance sp ectra of these ions is discussed. In the preceding paper (part I, Godfrey & Murrell 1964a) we compared two models for interpreting the spectra of substituted hydrocarbons. The localizedorbital model, which is ideally suited to molecules where there is little electron delocalization of the hydrocarbon and the substitutent electrons, was found to be more flexible for constructing a general theory which would include poly sub stituted hydrocarbons. In the localized-orbital model wave functions are built up in terms of orbitals localized on the hydrocarbon or on the substituent. There are two points to be considered. The first is how the substituent perturbs the transitions which are localized on the hydrocarbon: this is generally referred to as the inductive effect of the substituent. The second is how the substituent delocalizes these transitions over both the hydrocarbon and the substituent: this is called the mesomeric effect. These two effects can be treated separately for any state whose wave function and energy can be adequately calculated by first-and second-order perturbation theory. In this paper we shall compare two methods of obtaining quantitative estimates of the inductive effect on the ^-electrons (If) from e If V is the perturbation term in the Hamiltonian due to the potential field of the substituent (F = 2 V,^ where i labels a hydrocarbon ^-electron) then the change in i energy of an electronic transition T'0 -> xFr on substitution is given to second order by