Intrinsic deuterium/proton NMR isotope effects on carbon-13 chemical shifts: dependence on carbon hybridization and substitution

Abstract

Deuterium-induced NMR isotope shifts of 13C resonance frequencies, 'A(13C), have been measured for a variety of deuterium-labeled hydrocarbons. One-bond effects in ethane, ethylene, and acetylene, as well as in the corresponding phenyl compounds, where found to correlate linearly with carbon hybridization. Upon introduction of -substituents 'A(13C) increases. For methyl-and phenyl-substituted methanes the substituent effect is additive. Data for 1-monodeuterated «-alkanes give support for the steric origin of the well-known -effect on 13C chemical shifts. The torsional angle dependence of 3A(13C)-values shows maxima for dihedral angles of 0°and 180°and minima for 60°and 120°, respectively.

Hydrogen-Deuterium (H-D) Exchange Reaction of Warfarin in D2O Solution

“…The original peak gradually shortened and a new broad peak appeared shifted to a higher field, which seemed to be due to the heavy atom effect of CHD or CD 2 on C12. [9][10][11] Figures 2A and C show changes in the signal pattern on 14 methyl protons, in which the new higher shifted signals seem to be triplet. These changes were also due to the H-D exchange reaction of CH 3 , CH 3 →CH 2 D→CHD 2 →CD 3 and signal splittings to triplet were due to a coupling with deuterium.…”

“…These observations agree with a decrease in CH 2 and the appearance of CHD and CD 2 . The higher field shift of the new signal may be due to the heavy atom effect of deuterium [9][10][11] and the quadrupole effect to broaden the signal.…”

Isotope-induced chemical shifts1?12/13C(29Si) and57Fe NMR of organosubstituted 2,5-dihydro-1,2,5-azasilaboroles, a silole and their tricarbonyliron complexes

“…21 It is known that the isotope-induced chemical shifts 1  1/2 H( 13 C) are different for the axial and equatorial positions in cyclohexane. 24 A deuterium in an axial position exerts a slightly more negative effect than one in an equatorial position, which was explained by the difference in the bond lengths, C-H(D) axial > C-H(D) equatorial . 24 In the tricarbonyliron complexes 3 and 4 the SiMe groups are non-equivalent (see Fig.…”

“…24 A deuterium in an axial position exerts a slightly more negative effect than one in an equatorial position, which was explained by the difference in the bond lengths, C-H(D) axial > C-H(D) equatorial . 24 In the tricarbonyliron complexes 3 and 4 the SiMe groups are non-equivalent (see Fig. 4 for a representative 29 Si NMR spectrum), and their 1 J( 29 Si, 13 C) values differ significantly by 4.…”

Solvent and α-substituent perturbations of the 2H/1H isotope shifts in the 13C nuclear magnetic resonance of toluene-α-d3

“…For conjugated systems, the hyperconjugative model is useful in some instances (9). The model entails a breakdown of the Born-Oppenheimer approximation and assumes less efficient hyperconjugative electron donation by a C-D than a C-H bond.…”