engleski

Long Range Isotope Effects as a Conformational Probe

Intrinsic isotope effects in NMR spectra provide a wealth of information about molecular structural properties. Long-range isotope effects, i.e. those transmitted over many bonds away from the substitution site are of special interest since they can serve as a conformational probe in benzene derivatives of the following type Ph-Z-Ph where Z is the bridging group (C=C, CşC, C=N etc.). In a series of para-deuteriated benzene derivatives linear correlations between long-range isotope effects and molecular torsional angle of the intervening C_2=C_1-C_alpha=C_alpha', C_2=C_1-N=C_alpha' or C_2=C_1-C_alphaşC_alpha' bond fragments were found. Torsional angles were calculated using quantum chemical methods: semiempirical AM1 and ab initio 6-31 g*. Proposed correlations could be used in conformational analysis of benznene derivatives.

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