Adaptation of characteristic vector analysis to pKBH+calculations of very weak bases from incomplete ultraviolet spectral data

Abstract

An adaptation of characteristic vector analysis has been applied to incomplete u.v. spectral data of a very weak base only partially protonated in pure sulphuric acid, 3-cyano-5,5-dimethylcyclohex-2-en-1-one (1). The estimated pKBH+ value, –5.29, obtained from the HA acidity function is in very good agreement with those calculated from linear free energy relationships: pKBH+vs.σ+(–4.96) or pKBH+vs.σI, σR+(–4.93) and the extra-thermodynamic relationship of pKBH+vs.ΔHBF3°(–5.32) for a series of 3-substituted-5,5-dimethylcyclohex-2-en-1-ones. This statistical method can be generalized for compounds in which the protonation is very incomplete even in pure sulphuric acid and for which the u.v.–visible spectral data are limited.