The New Substituent Constants in the Excited States (II)

In order to standardize the ${\sigma}^*,\;{\rho}^*$ is taken as unity for the benzoic acids by analogy with the fact that ${\rho}$ of benzoic acids in the ground state is taken as unity. The $pK_{\alpha}^*$ of many benzoic acid derivatives are determined by UV spectroscopy and fluorescence spectral analysis whenever possible. The ${\sigma}^*$ constants are derived from the Hammett equation utilizing these $pK_{\alpha}^*$ values and the $pK_{\alpha}^*$ of the benozic acid derivatives showed better correlationship with ${\sigma}^*$ than ${\sigma},\;{\sigma}^+\;and\;{\sigma}^-$ as expected. From these ${\sigma}^*$ values, ${\rho}^*$ of the phenol derivatives was calculated to be 1.28. The new standardized ${\sigma}^*$ values are calculated from the $pK_{\alpha}^*$ values of phenols since more accurate and abundant data are available for phenols than the benzoic acid derivatives.