Nuclear shielding, deuterium isotope effects

The intrinsic and the equihbrium parts of the isotope effects can be separated. This was demonstrated in two different ways by Filarowski et al. [39] and Limbach et al. [41]. Filarowski et al. used the equations described earher combined with calculation of nuclear shieldings and isotope effects (see Sections 6.1 and 6.7). Limbach et al. used the geometric approach described in [20] illustrated in Figure 6.19a combined with an equihbrium approach. In Figure 6.19b, the one-bond deuterium... 

TABLE 35. Deuterium isotope effects on 13C and 15N nuclear shieldings in secondary 2-substituted enamines0... 

The amino substituent increases the nucleophilicity of the /Lcarbon due to the electron-donating power of the nitrogen and makes it useful in alkylation reactions368,369. Isotopically labelled enamines have been utilized to study the conjugation of the double bond with nitrogen in these and related compounds by investigating the deuterium isotope effects on 13C and 15N nuclear shielding in enamine derivatives. Mechanistic... 

Deuterium isotope effects on 13C and 15N nuclear shielding in enaminones, enamine esters and nitroenamines which often exist in solution as a mixture of E (1) and Z (2) isomers have been recently investigated1. When labelled with deuterium E and Z isotopomers are obtained. 

Deuterium isotope effects on C and N nuclear shielding in enamine... 

Deuterium isotope effects on and nuclear shielding in enamine derivatives... 

Despite the undeniable impact that NMR has had on progress in carbocation chemistry, it seemed to us surprising that there were no previous reviews in Annual Reports on NMR Spectroscopy that were entirely devoted to providing, under a certain umbrella, some of the NMR characteristics of certain classes of carbocations. Volume 14 (a comprehensive collection of l9F NMR data by V. Wray) contains 19F data for representative fluorinated carbocations. In volume 15, in a chapter on isotope effects on nuclear shielding (by P. E. Hansen), examples of deuterium isotope effects in classical and non-classical carbocations were included. However, there has not been a previous review entirely devoted to compiling NMR data on a large class or group of carbocations for comparative purposes. 

---