Deuterated molecules

A particularly interesting case is when a set of hydrogens which are chemically equivalent in the unionized molecule become inequivalent in the positive ion. Obvious examples are Jahn-Teller active molecules, but the same phenomenon may be found also in Jahn-Teller inactive systems. Since deuteration fcr practical reasons must be done before ionization, it may happen that a single deuterated molecule may produce several inequivalent isomers of the radical cation, e.g., upon irradiation. This will obviously influence the recorded ESR spectrum. 

P21212i Z = 4 D = 1.663 R = 0.024 for 1,863 neutron intensities at 123 K. This is a neutron-diffraction, low-temperature refinement of a partially deuterated molecule. The undeuterated molecule had previously been studied by neutron diffraction at room temperature.10 The experiment was performed in order to seek evidence of favored replacement of hydrogen by deuterium at the anomeric hydroxyl group, but no evidence therefor was observed. 

Perrin et al. probed the structures of 174 and 175 by using the 13C NMR method of isotopic perturbation of equilibrium <2001PCA11383>. The goal of this study was to measure the 13C NMR chemical-shift difference between C5 of a-deuterated molecule and C2-(5) of undeuterated molecule (see Equation 48). If 174 or 175 is a mixture of valence tautomers 180-r/ia and 180-r/]b or 181-equilibrium isotope shift (Aeq) will be observed in addition to the intrinsic isotope shift (5A0). In contrast, if 174 or 175 has C2v symmetry, then only (5A0) will contribute. 

FREQUENCIES (CM-1) OF THE VIBRATIONS OF X—H BONDS IN SOME SIMPLE MOLECULES (GAS PHASE UNLESS OTHERWISE SPECIFIED). THE r-F ACTOR IS THE RATIO OF THESE FREQUENCIES WITH THE CORRESPONDING ONES IN THE DEUTERATED MOLECULES. 

In this section we shall be concerned with the H species. The deuterated molecules will be considered in Section VIIIC... 

The desorbed species at 560 K does not contain deuterated molecules when CH3OD is used, indicating that methoxyl groups are also formed on p(lx2)-0 at low temperatures and are decomposed at 560 K. The main reaction path on the p(lx2)-0 surface can then be summarized as... 

In this field, the resolution of DMR is promising. However, experiments on deuterated molecules have just begun, and the nuclear relaxation was not yet analyzed. We can just present here some preliminary ideas that were obtained from proton relaxation experiments (19). Because of the nature of dipolar interaction, we are dealing with a multispin system this entails some complex problems of nuclear spin dynamics which are beyond the scope of this discussion. The quantitative analysis of proton relaxation data is thus far from straight-forward (20). We shall limit ourselves to a qualitative interpretation of the frequency dependence of the relaxation rate that is summarized schematically in Figure 4. Important relaxation effects appear in both high and low frequency regions. 

Fig. 10. The Lambert-Salter plot. Relation between Z1>0 and vmln for simple polyatomic molecules at 300 °K. Values listed in order from the bottom upwards. O, molecules containing no hydrogen atom C,Ft CF,Br, CF,BrCl CF,C1, CFC1S CClt CF,Br CF,C1 SF, CF, CS, NsO COS Cl, CO,. , molecules containing one hydrogen atom CHC1,F CHC1, CHC1F, CHF,. , molecules containing two or more hydrogen atoms CH,C1F CH,I CH,F, CH,Br C,H, CH,C1 C,H,0 C,H, cyclo-C,H, CH,F CH(. , deuterated molecule CD,Br.

The MS data (negative ESI mode) provide information on the molecular mass of the partially deuterated molecules due to the use of D20 in the eluent. The MS experiments, however, were carried out via flow injection analysis (FIA-MS) on peaks that were cut from a separate chromatographic run in which H20 was used instead of D20. In this way, in addition to the fragmentation, the... 

As detailed discussed in a previous section and elsewhere (Kohen and Limbach 2006), when the C-H bond breakage is a rate determining step, then the hydrogen substitution with deuterium leads to a measurable primary isotope effect with improved stability toward oxidation of the deuterated molecule or macromolecule in comparison to its hydrogenated counterpart (Jessop et al. 1994 Kohen and Limbach 2006). Figure 7.11 shows qualitatively this phenomenon when compared with Fig. 7.12 (first two spectra on top of the figure). The FT-IR spectrum of C70D38 after... 

Fig. 8.6 The kinetics of photolysis of both C7QH38 and C70D38 can be described by pseudofirst order law. The photolysis rate constant of C7ffH38 is 1.54 x 10 3 s 1 while the photolysis of C7QD38 occurs at a rate of 1.17 x 10 3 s 1. The differences in the two rate constant between the hydrogenated and deuterated molecule can be ascribed to primary isotope effects...

As shown in Fig. 8.7, the freshly prepared solution of C60H18 in n-hexane is characterized by three distinct maxima at 212, 260 and 340 nm (Palit et al. 1998). A similar spectrum is displayed by the deuterated molecule C60D18 in Fig. 8.8. Since the replacement of hydrogen with deuterium implies only a variation of mass of the substituents but not the electronic properties of the molecule. Thus, the two electronic absorption spectra are in Figs. 8.7 and 8.8 respectively due to C60H18 and its deuterated analogous are necessarily identical. 

The necessity to label (deuterate) the systems under study may often appear as a disadvantage, since it prevents working with real (industrially designed) materials. A way to circumvent this drawback is to use labelled (deuterated) molecules as 2H NMR probes of material properties [67]. 

Most deuterated solvents have residual proton impurities in an otherwise completely deuterated molecule thus, deuterated dimethyl sulfoxide, (CD,)2S=0, contains a few molecules of CD2H—(S=0)—CD3, which show a closely spaced quintet (/ 2 Hz, intensities 1 2 3 2 1) in accordance with 2nl + 1 (see Appendix G). 

Probing mechanism of the reaction involving intramolecular competition between different isotopic species at several chemically equivalent positions, the number of equivalent sites must be taken into consideration. In the case of deuterium content at natural abundance the concentration of multiply labelled molecule is negligible and not-deuterated molecules are invisible in the 2H NMR. When reaction is taken to the completion the retained and transferred deuterium can be calculated from the 2H spectra of substrate and product. The KIE is given by ... 

---