Collect. Czech. Chem. Commun. 1996, 61, 704-712

Chemometric Analysis of Substituent Effects. IX. Alternative Interpretation of Substituent Effects (AISE) - Orthogonal Model

Oldřich Pytela

Department of Organic Chemistry, University of Pardubice, 532 10 Pardubice, Czech Republic


Continuing the previous communications, the present paper suggests an orthogonal model of alternative interpretation of substituent effects (AISE). Following this approach, substituents are classified into three classes. Those of class II are defined as substituents whose atom bound to the basic skeleton bears a character of nucleophile, i.e. it is able of an intramolecular nucleophilic interaction with the reaction centre. The class III includes substituents whose atom bound to the basic skeleton is electrophilic in nature and can correspondingly interact with the reaction centre too. The class I includes the substituents possessing none of the above-mentioned characteristics. Within the model suggested the substituent effects can be described by a family of three lines corresponding to the substituent classes described with a single substituent constant at the coordinate axis. The validity of the model suggested has successfully been tested by comparison with other correlation equations using 318 reaction series taken from literature. It has been found that the value of the point of intersection at the coordinate axis (the isosubstituent constant) is smaller in processes with electron deficit and grater in those with electron excess in the reaction centre. The slopes of the individual lines in the family of lines (the reaction constants) decrease in the order II > I > III in most cases, the only exception being the processes with direct conjugation between a negatively charged reaction centre and the substituent and some gas phase processes.

Keywords: Chemometrics; Substituent effects; Alternative interpretation of substituent effects.