Structure and Conformational Analysis of 5-Methyl-2,2-diphenyl-1,3-dioxane
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cture and Conformational Analysis of 5-Methyl-2,2-diphenyl-1,3-dioxane A. E. Kuramshinaa, R. A. Khalikovb, V. A. Kataevb, T. V. Tyumkinac, E. S. Meshcheryakovac, L. M. Khalilovc, and V. V. Kuznetsova,d,* a b
Ufa State Petroleum Technological University, Ufa, 450062 Russia
Bashkir State Medical University, Ministry of Health of the Russian Federation, Ufa, 450008 Russia c
Institute of Petrochemistry and Catalysis, Russian Academy of Sciences, Ufa, 450075 Russia d
Ufa State Aviation Technical University, Ufa, 450008 Russia *e-mail: [email protected]
Received July 13, 2020; revised July 18, 2020; accepted July 26, 2020
Abstract—The structure of 5-methyl-2,2-diphenyl-1,3-dioxane has been studied by 1H and 13C NMR spectroscopy and X-ray analysis. Its molecules in crystal, as well as in CDCl3 and C6D6 solutions, have a chair conformation with equatorial methyl group. The conformational transformation pathways, ΔG0298 value for the 5-methyl group in CDCl3 and C6D6, and the optimal number of solvent molecules in the nearest solvation shell of 5-methyl-2,2-diphenyl-1,3-dioxane have been determined by quantum chemical calculations at the PBE/3ξ and RI-MP2/λ2 levels of theory and by comparing the theoretical and experimental vicinal spin–spin coupling constants. Keywords: 1,3-dioxane, X-ray analysis, NMR, conformer, cluster model, computer simulation
DOI: 10.1134/S1070428020100152 theory [11]; this computational method previously showed good results for 1,3-dioxane derivatives. In some cases, RI-MP2/λ2 calculations were performed using PRIRODA software [12]. 5-Methyl-2,2-diphenyl-1,3-dioxane (1) has not been reported previously. It was synthesized by condensation of 2-methylpropane-1,3-diol with benzophenone (Scheme 1). The structure of compound 1 in crystal was determined by X-ray analysis (Fig. 1; see Experimental). It crystallized in space group P21/n belonging to the monoclinic crystal system. The six-membered ring has a chair conformation with equatorial methyl group on C5 and expected C–O bond lengths (1.410– 1.430 Å) and bond angles in the heteroatom moiety (111–114°; Table 1) [10, 11]. The data of 1 H and 13 C NMR spectroscopy (Table 2) for solutions of 1 in CDCl3 and C6D6, includ-
1,3-Dioxane ring is present in many biomolecules with a broad spectrum of pharmacological activity [1]; therefore, 1,3-dioxane derivatives are quite promising for the design of new medicines [2, 3]. In addition, substituted 1,3-dioxanes are widely used as reagents in fine organic synthesis [4–6], in particular in regioselective reactions in carbohydrate chemistry [7] and in the preparation of chiral carboxylic acids [8] and 1,3-diols [9]; furthermore, 1,3-dioxanes are classical models for conformational analysis [10]. The present work was aimed at studying the effect of the solvent nature and number of its molecules on the relative energy of particular minima on the potential energy surface of 5-methyl-2,2-diphenyl-1,3-dioxane (1) (cluster model) and its structure and conformations by using 1H and 13 C NMR spectroscopy, X-ray analysis,
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