Selective deuteration

Selective Deuteration. Methods outlined earlier (6) were used. NaOD was used to deuterate selectively positions ortho and para to a free phenolic group, D3P04 to deuterate all aromatic sites, and NaOH to remove selectively deuterium from positions ortho and para to a free phenolic group. 

A variety of techniques including specific deuteration, selective proton decoupling, and lanthanide shift reagents (LSR), Pr(dpm)3, was used by Haines et al. (138) to assign completely the H and Si NMR spectra of methyl-2,3,4,6-tetra-O-trimethylsilyl-oc-D-glucopyranoside. This paper also presents the first LSR study in Si NMR. It shows that the magnitudes of the LSR induced shifts in the spectra are of the same order as those found for the Si resonances. (138)... 

Hexaborane(lO) may be deuterated selectively in the basal terminal positions by treatment with B2DJ in ether at — 20°C. This is in contrast to the higher T required for BjH,. Some H-D exchange occurs in the bridging position in B H,q, but either... 

Pentaborane(9) may be deuterated selectively at the apical position by treatment with DCl in the presence of AlClj at RT. 1-Deuteration is complete after 2 h, and l-DB,Hg containing 90% D at the 1-position may be prepared ... 

A comprehensive review on measurement of proton-proton couplings in the sugar part of a DNA molecule has been given by Kennedy and co-workers. The authors explored the influence of stereo-selective deuteration, selective excitation, decoupling and /-doubling on the accuracy of the measured couplings. 

Tx relaxation studies can determine the number of protons within two bond distances of a quaternary carbon nucleus. Other spectroscopic techniques applied to establish more rigorously the cmr assignments include selective single-frequency proton decoupling and nuclear Overhauser enhancement experiments. Chemical methods such as selective deuteration, selective C-13 incorporation, and shift reagent experiments have also been applied in some of the studies reported here. 

Selectivities to various isomers are more difficult to predict when metal oxides are used as catalysts. ZnO preferentially produced 79% 1-butene and several percent of i7j -2-butene [624-64-6] (75). CdO catalyst produced 55% 1-butene and 45% i7j -2-butene. It was also reported that while interconversion between 1-butene and i7j -2-butene was quite facile on CdO, cis—trans isomeri2ation was slow. This was attributed to the presence of a TT-aHyl anion intermediate (76). High i7j -2-butene selectivities were obtained with molybdenum carbonyl encapsulated in 2eohtes (77). On the other hand, deuteration using H1O2 catalyst produced predominantly the 1,4-addition product, trans-2-huX.en.e-d2 with no isotope scrambling (78). 

Isolated tetrasubstituted double bonds do not react under these conditions and the saturation of trisubstituted double bonds is extremely slow, thus limiting the general utility of the method. This difference in reactivity is used to advantage for the selective deuteration of the -double bond in androsta-l,4-diene-3,17-dione (138). In homogeneous solution, saturation usually occurs from the a-side and consequently the deuterium labels are in... 

Another example of selective deuteration in homogeneous solution is saturation of the sterically more accessible A -double bond in ergosterol acetate (142 143). The a-configuration of the incorporated deuteriums... 

Bromination of 3 -hydroxy-B-homo-5a-cholestan-7-one acetate (54b) in the presence of hydrobromic acid gives a single thermodynamically stable monobromo ketone. To determine the position of the bromine atom, the sequence of reactions was repeated with compounds selectively deuterated in the 5a-position. 

The increase of selectivity in consecutive reactions in favor of the intermediate product may be sometimes extraordinarily high. Thus, for example, in the already cited hydrogenation of acetylene on a platinum and a palladium catalyst (45, 46) or in the hydrogenation or deuteration of 2-butynes on a palladium catalyst (57, 58), high selectivities in favor of reaction intermediates (alkenes) are obtained, even though their hydrogenation is in itself faster than the hydrogenation of alkynes. 

Fig. 32. 2H spectra of a polymer model membrane, cf. Fig. 27b), selectively deuterated at the a-methylene group of the hydrophobic chain. The spectra are compared for the monomer as well as the polymer lamellar phases at the same temperatures, respectively... 

It was shown in the same article that the decarboxylation could also be performed by conventional heating but then copper cyanide was required and a mixture of saturated and imsaturated 2-pyridones 65 and 66 was obtained in a ratio of 1 10 (Fig. 10). A tentative mechanism was suggested for the reagent-free MAOS method where the carbonyl in the 2-pyridone ring is supposed to assist in the decarboxylation yielding an yUde 67 (Fig. 11). The decarboxylated bicyclic 2-pyridone 68 is thereafter obtained after protonation by the solvent. In agreement with the mechanistic suggestion, it was shown that a selective deuteration occurred when deuterated dimethyl sulfoxide (DMSO-de) was used as solvent. 

The use of selective deuteration is a powerful tool in electron spin resonance (ESR) experiments, in order to establish unequivocal assignments of experimental spectra of radicals. The reason for this is, as is well known, the difference in magnetic properties between the deuteron and the proton, which can be exploited to distinguish chemically inequivalent hydrogens in the molecule. 

We have previously in a number of papers [1-5] investigated these effects ft -both the Jahn-Teller inactive molecule n-butane [1] and the Jahn-Teller active molecules ethane, cyclopropane, and cyclohexane [2-5]. The choice of systems was largely dictated by the availability of experimental results [5-8]. New experiments being performed on selectively deuterated benzene have motivated a closer theoretical study of this system, and a first presentation of these investigations is given in the present paper. 

Fig. 3.—A. Initial Slope Approximation to Determine the Initial, Nonselective, Spin-Lattice Relaxation Rate of H-S of 2,3 S,6-Di-0-isopropylidene-a-D-mannofuranose (2) in Me2SO-d Solution. (Points between 0.01 and l.SS s were selected for tracing the best straight line.) B. The Same as in A for H-1 of a Partially Deuterated Sample of 1,6-Anhydro- -cellobiose Hexaacetate (3). [Note that the relaxation of H-1 is strongly dependent on the choice of I value. An R (ns) value of 0.24s was obtained from the data points 0 t 5s, where a value of 0.18 s was obtained from the terminal decay 5 lOs (see text).]...

Combinations of non-selective and/or single-selective relaxation-rates, or both, with n.0.e. values may conveniently be performed with reliable results, especially when other methods seem impractical. However, these experiments are time-consuming, as they entail the determination of a rather large number of experimental values. Moreover, the n.O.e. parameters carry their own systematic and random errors, which are magnified in the calculation of interproton distances. The deuterium-substitution method requires specific deuteration at a strategic position, which, in many cases, may be inconvenient or impractical. Also, this technique is valid only when the relaxation rates obtained after deuterium substitution are at least 5% enhanced, relative to the relaxation rates of the unsubstituted compound, and it requires that, for a meaningful experiment, the following condition " be satisfied. 

For a mechanistic investigation, hydroboration of myrcene with pinacolborane-di was examined. A selective deuteration was observed at the methyl group of the hydroboration product (Scheme 27). 

---