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Deuterium Isotope Effects in 13C NMR Spectra of Mono- and Binuclear Aromatic Compounds

Isotopic substitution produces changes in the reactivity of a molecule and causes a redistribution of molecular internal vibrational and rotational energy. In NMR, it causes changes in chemical shifts (nuclear shielding), coupling constants and relaxation times. The most studied by far are deuterium effects on nuclear shielding owing to the large fractional change in mass on isotopic substitution and relative ease of their determination from high resolution NMR spectra. The focus of this talk will be put to unsaturated systems containing one or two bridged phenyl groups where isotopic perturbation can be transmitted many bonds away from the isotope substitution site. The sign alternation and specific magnitudes of such long range isotope effects will be discussed in terms of subtle charge shifts throughout the molecule as a consequence of bond shortening upon isotopic substitution. Moreover, the linear correlation between long-range isotope effects and molecular torsional angle can serve as a conformational probe [1] for studied type of molecules. [1] P. Novak, D. Vikić Topić, V. Smrečki, and Z. Meić, Isotope Effects in NMR Spectra as a Structural Tool for Organic Molecules, in: Atta ur Rahman (Ed.), New Advances in Analytical Chemistry, Harwood Academic Publishers, Amsterdam, 2000, 135- 168.

deuterium isotope effects, NMR chemical shifts, binuclear aromatic compounds

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