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. 2020 Apr 28;25(9):2061.
doi: 10.3390/molecules25092061.

Substituent Effects on NMR Spectroscopy of 2,2-Dimethylchroman-4-one Derivatives: Experimental and Theoretical Studies

Daniela Iguchi  1   2 , Davide Ravelli  3 , Rosa Erra-Balsells  1 , Sergio M Bonesi  1   3
Affiliations

Substituent Effects on NMR Spectroscopy of 2,2-Dimethylchroman-4-one Derivatives: Experimental and Theoretical Studies

Daniela Iguchi et al. Molecules. .

Abstract

The attribution of 1H and 13C NMR signals of a library of 5-, 6- and 7-substituted 2,2-dimethylchroman-4-one derivatives is reported. Substituent effects were interpreted in terms of the Hammett equation, showing a good correlation for carbons para- to the substituent group, not for the meta- ones. Similarly, the Lynch correlation shows the additivity of the substituent chemical shifts in the case of both H and C nuclei, again with the exception of the carbons in the meta- position. Density Functional Theory (DFT)-predicted 1H and 13C chemical shifts correspond closely with experimentally observed values, with some exceptions for C NMR data; however, the correlation is valid only for the aromatic moiety and cannot be extended to the heterocyclic ring of the chroman-4-one scaffold.

Keywords: Hammett correlation; Lynch correlation; NMR spectroscopy; density functional calculations; oxygen heterocycles.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Structures of substituted 2,2-dimethylchroman-4-one derivatives studied in this work.
Figure 1
Figure 1
Lynch correlations of 2,2-dimethylchroman-4-one derivatives belonging to Series 1: (a) 1H and (b) 13C correlations; the inset in (b) shows the profile of carbons meta- to the substituent R (C-4a and C-8).
Figure 2
Figure 2
Hammett correlations between the 13C chemical shift values (δ(C-X)) of substituted 2,2-dimethylchroman-4-one derivatives and Hammett substituent constants (σp+ or σm, depending on the considered C-atoms): (a) carbon atoms in para- position (Series 1–3), and (b) carbon atoms in meta- position (Series 1) with respect to the substituent R.
Figure 3
Figure 3
Correlation between experimental (δEXP) and theoretical DFT (δTHEOR) chemical shifts for: (a) H-ortho; (b) H-meta; (c) H-para with respect to the substituent R group and (d) methylene CH2 moiety in substituted-2,2-dimethylchroman-4-ones of Series 1, 2 and 3; the data in the gray circles have not been considered for building the linear correlations (see text for details).
Figure 4
Figure 4
Correlation between experimental (δEXP) and theoretical DFT (δTHEOR) chemical shifts for: (a) C-ipso; (b) C-ortho; (c) C-meta and (d) C-para with respect to the substituent R group in substituted-2,2-dimethylchroman-4-ones of Series 1, 2 and 3.
See this image and copyright information in PMC

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