The spectra of a number of substituted benzoic acids, acetanilides, and phenyl benzoates are discussed in terms of the electronic and steric effects of substituerrts. INTRODUCTIONThe absorption band observed in the 230 mp region of the absorption spectrum, and designated by iMoser and Icohlenberg (12) as the B-band, is of interest in the orfho-substituted benzoic acids, since the usual explanation of the steric effect due to an ortho-substituent must be modified in order to account for the observed spectra.The for~nula of benzoic acid may be written in two forms, one possessing an intact carboxyl group (type IA), the other a hydrogen-bridged structure (type IB). On steric considerations alone, neither form accounts satisfactorily for all of the ortho-substituted benzoic acid spectra (see Table I). For example, supposing o-toluic acid exists as structure IA (R = Me), no unusual loss of intensity should be apparent since a similar coilformation may be shown to be relatively insensitive to steric eflects involving excited states only in o-methylacetophenone (8), where the OH group of IA is replaced b l~ a methyl group. In o-toluic acicl, however, there is observed a pronounced l~ypsocl~romic shift accompanied by almost complete loss of intensity of absorption as coinpared to p-toluic acicl. Similarly, if IB (R = Me) alone were the correct configuration, and one ortho-methyl substit~ient mas to produce a twist in the carbon-carbon linkage sufficient to accommoclate the substituent, a second methyl substituent in the other ortho-position would not be expected to bring about much further change in the observed spectrum. However, in 2,G-cliinetl~ylbei~zoic acid the band in this region has disappeared complete1 y (12).Hence it may be concl~~cled that the observed changes in the B-band of the spectra of substituted benzoic acids are primarily due to the electrical effects of substituents, which is not unexpected since an isolated C=O group is known lManuscript received Augz~st 9,1955. Contribution from the