Experimental and GIAO 15N NMR study of substituent effects in 1 H -tetrazoles

Abstract

A series of 1-aryl/alkyl-1H-1,2,3,4-tetrazoles, 5-substituted 1H-tetrazoles, and 1,5- and 2,5-disubstituted 1H-tetrazoles were studied by a combination of experimental NMR (natural abundance 15N, 15N/ 1H HMBC, and 13C) and computational GIAO-NMR techniques to explore substituent effects on 15N (and 13C) NMR chemical shifts in the tetrazole (TA) moiety. Computed 15N chemical shifts via GIAO-B3LYP/6-311+G(2d,p) calculations gave satisfactory results in comparison with experimental data. Whereas N-alkylation leads to large 15N chemical shift changes, changes in the N 1-aryl derivatives bearing diverse substituent(s) are generally small except for polar ortho-substituents (COOH, NO 2). Large δδ 15N values were computed in N 1-aryl derivatives for p-COH 2 + and p-OMeH + as extreme examples of electron-withdrawing substituents on a TA moiety. © 2012 American Chemical Society.