Substituent effects on scalar J(13C, 13C) couplings in pyrimidines. An experimental and DFT study |
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Authors: | de Kowalewski Dora G Díez Ernesto Esteban Angel L Barone Verónica Peralta Juan E Contreras Rubén H |
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Institution: | Departamento de Física, FCEyN, Universidad de Buenos Aires, Ciudad Universitaria, P. 1 and CONICET (C1428EHA), Buenos Aires, Argentina. |
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Abstract: | One- two- and three 13C, 13C (n = 1, 2, 3) scalar couplings, (n)J(C,C) in a set of pyrimidine derivatives were studied both experimentally at natural abundance and theoretically by their DFT calculation of all four contributions. Trends of non-contact terms are discussed and substituent effects are rationalized, comparing some of them with the corresponding values in benzene and pyridine. Although substituent effects on non-contact terms are relatively important, the whole trend is dominated by the Fermi contact term. According to the current literature, substituent effects on 1J(C,C) couplings in benzene derivatives are dominated by the inductive effect, which, apparently, is also the case in nitrogen heteroaromatic compounds. However, some differences observed in this work for substituent effects on 1J(C,C) couplings in pyrimidine derivatives suggest that in the latter type of compounds substituent effects can be affected by the orientation of the ring nitrogen lone pairs. |
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Keywords: | NMR 13C NMR J(C C) scalar couplings pyrimidines lone‐pair orientation effect hyperconjugative interactions dual path transmission |
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