Conformational analysis, experimental and GIAO-DFT ¹³C NMR chemical shift calculation on 2’-hydroxy-3,4,5-trimethoxy-chalcone
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2017-03-31
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In this paper we investigated the ability of the GIAO-mPW1PW91/6-31G(d)//mPW1PW91/6-31G(d)
level of theory to predict the 13C nuclear magnetic resonance (NMR) chemical shifts of the 2’-hydroxy3,4,5-trimethoxy-chalcone molecule. Two different approaches were used. First: the absolute
shieldings σ for all carbon atoms in each geometrically optimized conformers of the 2’-hydroxy3,4,5-trimethoxy-chalcone molecule were calculated at the GIAO-mPW1PW91/6-31G(d)//
mPW1PW91/6-31G(d) level of theory. This approach is further used to generate weighted average
values for each atom considering the previously obtained conformational distribution. Second: only
the σ for the lowest energetic conformer will be taken to account. The robustness of the method
was evaluated for two other chalcones: (E)-1-(4-hydroxy-3-methoxyphenyl)-3-(3,5-di-tert-butyl4-hydroxyphenyl)prop-2-en-1-one and (E)-1-(4-aminophenyl)-3-(3,4-dimethoxyphenyl)prop-2-en1-one, corroborating the ability of the method in chemical shift prevision. Although, both approaches
were able to reproduce the chemical shifts of the 2’-hydroxy-3,4,5-trimethoxy-chalcone, significant
differences in the calculated values for C-4 and methoxy carbons were observed. The best results
were obtained using the second approach (II).
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Chalcone, 2’-hydroxy-3,4,5-trimethoxy-chalcone, GIAO-NMR, Scaling factor, NMR spectroscopy
Citação
COSTA, Fabio Luiz P. et al. Conformational analysis, experimental and GIAO-DFT ¹³C NMR chemical shift calculation on 2’-hydroxy-3,4,5-trimethoxy-chalcone. Journal of the Brazilian Chemical Society, Campinas, v. 28, n. 11, p. 2130-2135, 2017. DOI: 10.21577/0103-5053.20170060. Disponível em: https://jbcs.sbq.org.br/default.asp?ed=259. Acesso em: 16 fev. 2024.