Directionality of intrinsic deuterium isotope effects in C-13 NMR spectra of molecules containing one or two phenyl groups

Novak, Predrag (1998) Directionality of intrinsic deuterium isotope effects in C-13 NMR spectra of molecules containing one or two phenyl groups. Croatica Chemica Acta, 71 (3). pp. 549-555. ISSN 0011-1643

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Abstract

Intrinsic deuterium-induced isotope effects have been measured and analyzed for compounds having one or two phenyl groups specifically labelled at different positions in a molecule. Some typical examples of directional and orientational dependence of the effects have been given. Different magnitudes of isotope effects that are transmitted in opposite directions have been observed. Thus, in p-H-2-cis-stilbene, the effect over six bonds at C-alpha of 8.7 ppb is found, while the corresponding effect in alpha-2H-cis-stilbene at C-4 is only 1.4 ppb. Similarly, in o'-H-2-trans-N-benzylideneaniline, the effect over six bonds at C-2,6 is 1.7 ppb, whereas that in o-H-2-trans-N-benzylideneaniline at C-2',6' is equal to zero Similar behaviour was observed in other molecules and at other positions as well. Additional factors contributing to the magnitude and sign of isotope effects, such as pi-electron delocalization, conformation, steric hindrance and lone pair electrons are also discussed.

Item Type:

Article

Uncontrolled Keywords:

chemical-shifts; cis-stilbene; trans-stilbene; one-bond; dependence; benzylideneaniline; hybridization

Subjects:

NATURAL SCIENCES > Chemistry

Divisions:

NMR Center

Projects: