Experimental and GIAO 15N NMR Study of Substituent Effects in 1H-Tetrazoles
2012
Aridoss, Gopalakrishnan | Zhao, Chunqing | Borosky, Gabriela L. | Laali, Kenneth K.
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 N₁-aryl derivatives bearing diverse substituent(s) are generally small except for polar ortho-substituents (COOH, NO₂). Large Δδ¹⁵N values were computed in N₁-aryl derivatives for p-COH₂⁺ and p-OMeH⁺ as extreme examples of electron-withdrawing substituents on a TA moiety.
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