Directionality of Intrinsic Deuterium Isotope Effects in 13C NMR Spectra of Molecules Containing One or Two Phenyl Groups

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-2H-cis-stilbene, the effect over six bonds at C-α of 8.7 ppb is found, while the corresponding effect in α-2H-cis-stilbene at C-4 is only 1.4 ppb. Similarly, in o\u27-2H-trans-N-benzylideneaniline, the effect over six bonds at C-2,6 is 1.7 ppb, whereas that in o-2H-trans-N-benzylideneaniline at C-2\u27,6\u27 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 π-electron delocalization, conformation, steric hindrance and lone pair electrons are also discussed

Directionality of Intrinsic Deuterium Isotope Effects in 13C NMR Spectra of Molecules Containing One or Two Phenyl Groups

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-2H-cis-stilbene, the effect over six bonds at C-α of 8.7 ppb is found, while the corresponding effect in α-2H-cis-stilbene at C-4 is only 1.4 ppb. Similarly, in o\u27-2H-trans-N-benzylideneaniline, the effect over six bonds at C-2,6 is 1.7 ppb, whereas that in o-2H-trans-N-benzylideneaniline at C-2\u27,6\u27 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 π-electron delocalization, conformation, steric hindrance and lone pair electrons are also discussed

Adriatic NMR Conference 2020

Adriatic NMR Conference 2020 September 22–24, 2020, Peroj (Istria), Croatia https://adriatic-nmr-conference.chem.pmf.hr/ This work is licensed under a Creative Commons Attribution 4.0 International License