Semenov VA, Samultsev DO, Krivdin LB. Substitution effects in the
15 N NMR chemical shifts of heterocyclic azines evaluated at the GIAO-DFT level.
MAGNETIC RESONANCE IN CHEMISTRY : MRC 2018;
56:767-774. [PMID:
29504638 DOI:
10.1002/mrc.4731]
[Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Revised: 02/18/2018] [Accepted: 02/20/2018] [Indexed: 06/08/2023]
Abstract
A systematic study of the accuracy factors for the computation of 15 N NMR chemical shifts in comparison with available experiment in the series of 72 diverse heterocyclic azines substituted with a classical series of substituents (CH3 , F, Cl, Br, NH2 , OCH3 , SCH3 , COCH3 , CONH2 , COOH, and CN) providing marked electronic σ- and π-electronic effects and strongly affecting 15 N NMR chemical shifts is performed. The best computational scheme for heterocyclic azines at the DFT level was found to be KT3/pcS-3//pc-2 (IEF-PCM). A vast amount of unknown 15 N NMR chemical shifts was predicted using the best computational protocol for substituted heterocyclic azines, especially for trizine, tetrazine, and pentazine where experimental 15 N NMR chemical shifts are almost totally unknown throughout the series. It was found that substitution effects in the classical series of substituents providing typical σ- and π-electronic effects followed the expected trends, as derived from the correlations of experimental and calculated 15 N NMR chemical shifts with Swain-Lupton's F and R constants.
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