Calculated polar substituent effects on the stability of 4-substituted(X) - cub-1-yl and -bicyclo[2.2.2]oct-1-yl cations: a DFT study

Abstract

The effects of substituents on the stability of 4-substituted(X) cub-1-yl cations (2), as well as the benchmark 4-substituted(X) bicyclo[2.2.2]oct-1-yl cation systems (7), for a set of substituents (X = H, NO2, CN, NC, CF3, COOH , F, Cl, HO, NH2, CH3, SiH3, Si(CH3)3, Li, O−, and NH) covering a wide range of electronic substituent effects were calculated using the DFT theoretical model at the B3LYP/6-311 + G(2d,p) level of theory. Linear regression analysis was employed to explore the relationship between the calculated relative hydride affinities (ΔE, kcal/mol) of the appropriate isodesmic reactions for 2/7 and polar field/group electronegativity substituent constants (σF and σχ, respectively). The analysis reveals that the ΔE values of both systems are best described by a combination of both substituent constants. This highlights the distinction between through-space and through-bond electronic influences characterized by σF and σχ, respectively. Copyright © 2010 John Wiley & Sons, Ltd.