Methyl deuterons

Fig. 23. Experimental and calculated methyl-deuteron spectra of polycarbonate for different temperatures and different evolution times Tr For the definition of cf. Fig. 13. The width of the distribution of correlation times is 2.7 decades...

At temperatures higher than - 70 °C, the methyl deuteron line shape corresponds to rapid rotation of the methyl group. This rotation in the rapid exchange limit leads to an averaged field gradient tensor, whose principal axis is along the spatially fixed C - CH3 bond direction. As there is not any... 

Solvated electrons appear to be characteristic of small anions with regard to their equilibrium solvation shell structures. For example, the OH bond orientation of water around solvated electrons can be compared with the same water orientation around fluoride ion in hydrated crystals of KF [Be 64]. Electron spin echo modulation studies have been suggested [Ic 80] therefore for the study of the solvation shell structure of anions. Tetracyanoethylene anion (TCNE ) was found to be a suitable model. The investigations were performed in the frozen solutions with CD3OH, CH3—OD, CD3CO and ( 03)280 at 4.2 K temperature. The results indicated that TCNE" is solvated by four methanol molecules with the methanol molecular dipole oriented toward the anion the distances from the anion to the hydroxyl and methyl deuterons are 0.59 and 0.38 nm, respectively. TCNE" is solvated by two molecules of acetone or dimethyl sulphoxide it is suggested that these solvating molecules are above and below the TCNE" plane with their molecular dipoles oriented toward the C=C bond in TCNE". 

In the spectra of alkyl cobinamides two peaks have been observed at 3.89 and 4.42 which were assigned to the protons of a water molecule coordinated at the lower axial site (130). To confirm this assignment, it was found that addition of cyanide to methyl cobinamide, which displaces coordinated water, caused the peaks to disappear. Likewise, addition of excess D2O caused disappearance of the peaks through either ligand exchange or proton-deuteron exchange. 

With time, the CD3 group is distributed throughout the system resulting in the formation of (CH3) (CD3)4- Pb (n = 3, 2, 1) and (CH3) (CD3)3- PbCl (n = 2, 1), as shown in Scheme 32. These species were used to determine the effect that a deuteron positioned four bonds away, 13, would have on the proton chemical shifts of a methyl group. These long-range four-bond deuterium isotope effects, 4AH( ) ), are summarized in Table 14. 

Proton ENDOR and DOUBLE ENDOR data on VO(acac)2 in frozen solutions have been reported by van Willigen2895. Since the CH-protons exchange with deuterons in CD3OD they may easily be discriminated from the methyl protons. From the single crystal-like ENDOR spectrum for B0 along g and the two-dimensional powder spectrum at gi, the hf coupling constants Ap 5 = 0.7 MHz and AfHj = 0.7 MHz, A 3 = 1.5 MHz, respectively, have been found. The relative signs of the principal... 

The electrophile E+ attacks the unhindered side of the still unsubstituted second aromatic ring. A proton (deuteron) is transferred from this ring to the second, originally substituted ring, from which it leaves the molecule. Thus, the electrophile enters, and the proton (deuteron) leaves the [2.2]paracyclophane system by the least hindered paths. Some migration of deuterium could be detected in the bromination of 4-methyl[2.2]paracyclophane (79). The proposed mechanism is supported by the kinetic isotope effects ( h/ d) found for bromination of p-protio and p-deuterio-4-methyl[2.2]paracyclophanes in various solvents these isotope effects demonstrate that proton loss from the a complex is the slowest step. 

Deuteron -NMR measurements on the same system (labelled in the methyl group) also show that the mobility of the hydrophilic ammonium head group is reduced by... 

Quadrupolar interactions can offer direct information on the dynamics of organics within zeolite crystals. Eckman and Vega (304) studied the 2H quadrupolar echo decay in perdeuterated p-xylene adsorbed on zeolite ZSM-5. The deuterium quadrupolar interaction usually dominates the spin Hamiltonian, so that the powder pattern can be used as a test for models of molecular motion. At -75°C and 25°C typical rigid-lattice spectra were obtained. At 100°C however, the resonance arising from the aromatic deuterons was motionally narrowed, while the methyl resonance was not, The authors conclude that p-xylene molecules reorient about an axis which passes through the C3 axes of the methyl groups. 

The directions of the principal components of the COO chemical shift tensor are shown in Fig. 114. The 022 axis makes an angle of 6° with the direction of the C = O bond and the <733 axis is perpendicular to the COO plane. The local chain axis is approximately perpendicular to the COO plane and nearly parallel to the <733 axis within about 20°. Finally, the C3 axis of the rotating methyl group, designated as zmethyl > is the unique axis of the quadrupolar interaction of the deuterons of the (0)CH3 group. 

The direct attack of proton from the solvent on the intermediate dihydropyridine as well as the over-all mechanism of the reduction received support from the extent and position of deuterium labeling in the product from the reduction of l-methyl-4-phenyl-pyridinium iodide (7) with sodium borohydride in dimethylformamide and deuterium oxide. The l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (9) formed was shown by nuclear magnetic resonance (NMR) and mass spectral analysis to contain approximately one deuterium atom located at the 3-position.13,14 This is the result to be expected from the pathway shown in Eq. (3) if the electrophile were a deuteron. 

The example illustrates, for example, two rotating methyl groups undergoing a two-site jump—as in dimethyl sulfone. Grouping the six deuterons as 1,2 and 3 on the first carbon and 4,5, and 6 on the second carbon, the Aj matrices are calculated for the combined rotation in the three-site jump and the two-site jump. 

By use of 13C CP MAS NMR (crosspolarization/magic angle spinning) and X-ray diffraction the structure of 3(5)-methyl-4-nitropyrazole in the solid state was examined [252], Desmotropy in azoles has been revealed for the first time. This means that the two tautomers, 3-methyl-4-nitro- and 5-methyl-4-nitropyrazole, are crystallized in two different crystals [252, 256], The problem of proton transfer in solid-state heterocycles, including nitropyrazoles, was studied by CP MAS NMR and X-ray structural analysis [253, 257], The kinetics of degenerate intermolecular triple proton and deuteron transfers in the cyclic trimer of polycrystalline 4-nitrop-yrazole (15N-labeled) has been studied as a function of temperature and is compared to the kinetic of triple proton transfer in bulk solid 3,5-dimethylpyrazole. The results show that the transfer kinetics in the new trimer is much faster than that in 3,5-dimethylpyrazole. Nevertheless, the kinetics of HHH/HHD/HDD/DDD isotope effects of 4-nitropyrazole is similar to that of 3,5-dimethyl derivative [257]. 

Fragmentations may be governed by steieoelectronic factors.The steroidal oxime (52 equation 34) fragmented with loss of a deuteron from the 4a-methyl group, whereas the analog (53 equation 35) fragmented with proton abstraction from the 43-methyl group. - ... 

Hollander and Prins investigated the effect of pressure on the glass-transition temperature Tg in atactic polypropylene in the pressure range up to 5000 bar. The decay rate of the deuteron-NMR quadrupole echo was used to monitor the glass transition. In further papers the same authors also studied the methyl group, segmental and chain motions of this molecular system. 

Fig. 3.2.5 [Miill] Deuteron wideline spectra for different motional mechanisms and times tc-The angle between the axis of rotation and C—bond (principal axis Z of the quadfupole coupling tensor) is denoted by d. (a) Twofold jump with 9 — 60° (b) Twofold jump with 9 = 180° (flips of p phenylene). (c) Three-fold jump with 9 = 109° (rotation of a methyl group), (d) Rotational diffusion on a cone 9 = 109°. (e) Tetrahedral jump, (f) Isotropic rotational diffusion.

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