Deuterium-induced isotope

A similar situation occurs in acetyl fluoride, where the nonlinearity of deuterium-induced isotope shifts on the 19F NMR signal implies a fractional population >1/3 for the conformer of CH2DCOF with C-D anti to F (38) and a fractional population <1/3 for the conformer of CHD2COF with C H anti to F (39).109 These populations arise because of the greater zero-point energy of a C H bond anti to F. They can be translated into deuterium IEs on the acidities of the conformers of acetyl or acetyl-d fluoride. 

The replacement of hydrogen atoms with deuterium caused large deuterium-induced isotope shifts in the 77Se NMR. For both conformers 45 and 46, the resonance of the deuterated compound shifted upfield with respect to the parent compound. The isotope shift (AS, an upfield shift) was 4.22 ppm for 45 and 4.03 ppm for 46. These values were definitely larger than that observed for 46 (AS = 3.78 ppm). These differences, AAS = +0.44 ppm for 45 and +0.25 ppm for 46, can be considered as the isotope shifts due to the C-H- -Se nonbonded interaction <1996BCJ1825>. 

Also known are the deuterium-induced isotope effect on the Sn shielding of —0.05 ppm/D and the primary isotope effect of —11.6 7 Hz for Sn—H spin-spin coupling for the SnDnH3 + cations generated in fluorosulfuric acid at low temperature from SnD H4 . The chemical shift of 208 ppm found in the Sn NMR of the reaction mixture of Me4Sn and SbCls was attributed to the Me3Sn+ cation. 

The first, and so far only, experiments in the pulsed mode are those by Epperlein et al (207) who provide shielding data for the chromate ion as a function of counter-ion and concentration. The deuterium induced isotope effect for the chromate system is 1 -3 ppm with a higher... 

Recently, deuterium-induced isotope effects on Li chemical shifts in organolithium compounds have been observed [51] and based on this observation, the isotopic fingerprint method was developed as a tool for structural investigations in the field of organolithium compounds. With this method, typical Li multiplets, which are characteristic of the aggregation state. 

Figure 5 Deuterium-induced isotopic fingerprints in Li NMR spectra of partially deuteriated organolithium aggregates (a) phenyllithium monomer (THF/penta-methyldiethylenetriamine — 122°Q (b) phenyllithium dimer (Et20/tetramethylethyl-enediamine -111°C) (c) methylhthium tetramer (R=CHj EtjO, — 92 Q (d) fluxional phenyllithium tetramer (Et20, — 102 C). The measu H/ H isotope shifts for 5( Li) are 19.2, 10.4, 15.6, and 7.0 ppb, respectively. All systems were Li labelled and 50% of the organic ligands were perdeuterated v C Li) = 58.88 MHz...

CP/MAS), gated H-decoupling techniques, deuterium-induced isotope effects chemical shifts, and molecular modeling has shown that this... 

Very recently an isotopic finger print method which rests on deuterium-induced isotope shifts for Li resonances has been proposed by Gunther and exemplified with applications from the aggregation behavior of cyclopropyllithium systems and mixed aggregates formation between methyllithium and lithium salts. By using one- and two-dimensional NMR experiments based on scalar spin-spin coupling and nuclear overhauser effects the structural aspects associated with benzyllithium and the formation of polylithium systems by lithium reduction of biphenylenes have been discussed. 

The introduction of isotopes into a compound alters the coupling pattern and the chemical shifts of the observed spectrum. As shovm in Eigure 1.18, deuterium-induced chemical shift variations have allo ved the estimation of the ratio of isomers 90a-d formed in Eq. (2) vhen R = Ph, R = CHjCOOH, and DCOOD/ Et3N is used for the hydrogen transfer [136]. The three sp -carbons Cl, C2 and C3 each afford a distinct singlet for the four possible isotopomers 90a-d (replacement of by shifts the resonances of the adjacent carbon nuclei to lo ver frequency) [137]. 

Thermolysis of l,l-difluoro-2,3-diphenylcyclopropane in supercritical CO2 has allowed the rate of geometrical isomerization [i.e. cis-( 109) to /ra/M-(109)] and racemization [i.e. (/< )-( 109) to (S)-( 109)] to be determined from O2 dependence of the trapping rate of the postulated intermediate 1,3-biradical.246 Above 150 °C, the formation of 2,2-difluoroindane and its decomposition products is reported. A similar thermally induced equilibrating series of stereomutations has been observed with the analogous non-fluorinated cyclopropane in which rate constants and deuterium exchange isotope effects are reported.247 Theoretical studies of this isomerization have focused on classical248 and quasi-classical trajectories.249... 

According to deuterium-induced upfield H NMR isotope shifts in partially deuterated rigid cyclohexane-1,3-diols dissolved in CDC13 or benzene-c/6, the OH is preferentially solvent-exposed, while deuterium prefers to reside in the intramolecular hydrogen bond (49).121 In acetone-c/6 and DMSO-c/6 downfield isotope shifts indicate that the OH preferentially resides in the intramolecular hydrogen bond, while OD forms an external hydrogen bond to the acceptor solvent, S (50). 

The competition between nucleophilic substitution and base-induced elimination in the gas phase has been studied using deuterium kinetic isotope effects (KIE).6 The overall reaction rate constants and KIE have been measured for the reactions of RC1 + CIO- (R = Me, Et, t -Pr, and r-Bu). As the extent of substitution in the alkyl chloride increases, the KIE effects become increasingly more normal. These results indicated that the E2 pathway becomes the dominant channel as the alkyl group becomes more sterically hindered. 

The most important NMR parameters obtained for the hydroxyl protons are chemical shifts (6), vicinal proton-proton coupling constants (3J7hc,Oh), temperature coefficients (AS/7), deuterium-induced differential isotope shifts, and exchange rates ( ex)-119-123 These parameters may provide information on hydrogen bond interactions and hydration as well. Moreover NOEs and chemical exchanges involving hydroxyl groups observed by NOESY and ROESY experiments also add to the number of distance restraints used in conformational analysis. 

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