Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The x-ray structure of methyl 5-nitro-2-methylbenzoate was determined [M,r = 195.17, monoclinic, P,21/c, a, = 7.265(1), b, = 7.749(1), c, = 16.526(3) Å, α; = 91.50(2)., V, = 930.0(3) Å3, Z, = 4, D,x = 1.39 g cm-3, Cu Kα, Λ = 1.5418 Å, μ = 9.56 cm-1, F,(000) = 408, T, = 291 K, R, = 0.081 for 1295 observed reflections]. In contrast to the planar molecule of the corresponding acid, studied previously, the carboxylate group in the ester molecule is twisted through an angle 25° from the ring plane. This torsion angle was estimated to be 65° in benzene solution; the estimation was based on the dipole moment and that of methyl 2-methylbenzoate. For the corresponding ethyl esters a value of 79° was found in a similar way. Although these results are expressed in terms of one non-planar conformation, the alternative explanation of an equilibrium of two planar forms is not excluded in solution. The only safe conclusion is that the energy differences are small and the conformation is sensitive both to the conditions and to small changes in structure; a large part of the observed effects of an ortho,-methyl group are due to reasons other than to the hindered resonance.
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