Deuterium distribution

Deuterium distributions in methyl pyruvate and methyl lactate (X = H or D) ... 

TABLE 2.3 Deuterium Distributions in Saturated Products at 100% Deuteriumation of a,P-Unsaturated Compounds119... 

FIGURE 2.27 Two possible mechanisms to explain deuterium distributions resulting from deuteriumation and exchange of methyl vinyl ketone. Deuterium is assumed to move subsurface and to attack adsorbed carbons from threefold hollows. Path A multiple exchange by repeated addition-rotation-abstraction at the [3-carbon (classic mechanism) path B I -A hydrogen shift followed by desorption as enol. 

Fig. 28. SIMS profiles of the deuterium distribution in a sample of (100) silicon after an implantation dose of 1.0 x 1016 2H/cm2 at 120 keV, and after subsequent anneals of 20 min. at various temperatures (Wilson, 1986).

Methanolysis of 26-ad gave mainly the product of a-elimination, phenylethyne (30), but a small amount of substitution product 29 was also obtained (eq 13). 16b The deuterium distributions in the isomeric products ( )-29 and (Z)-29 are very interesting and shed light on the reaction mechanisms for their formation. Due to the basicity of methanol, the main reaction path becomes a-elimination. The deuterium is completely scrambled in the E isomer of 29, as observed in the products of trifluoroethanolysis. In contrast, the Z isomer of 29, the product of inversion, retains the deuterium at the original a position. The best interpretation is that ( )-29 is formed via phenyl participation while (Z)-29 is produced via the in-plane SN2 reaction. 

The two mechanisms may result in substantial and characteristic differences in deuterium distribution. The metal hydride addition-elimination mechanism usually leads to a complex mixture of labeled isomers.195 198 208-210 Hydride exchange between the catalyst and the solvent may further complicate deuterium distribution. Simple repeated intramolecular 1,3 shifts, in contrast, result in deuterium scram-bling in allylic positions when the ir-allyl mechanism is operative. ... 

The monohydrogenation of conjugated dienes can occur by either 1,2 or 1,4 addition. 1-Butene (53%) and trans-2-butene (42%) are the main products in the hydrogenation of 1,3-butadiene on palladium with only a small amount of cis-2-butene.68 Deuterium distribution reveals that the trans isomer is produced by 1,4 addition. 

Nn, and to the ratio a/b such that the calculated deuterium distribution, derived from the IV-profile, is in good agreement with the experimentally observed distribution. This method has been used by Wells and co-workers [166,167] to interpret the deuterobutene distributions observed in the catalysed hydrogenation of buta-1 3-diene (see Sect. 4.9). 

Fig. 11. Deuterium distributions in irons- and ris-2-butenes (a) and in butane (b) formed in the reaction of 1-butene with D2 on MoS2 at room temperature.

Scheme 9. Deuterium distribution in n-butenes formed by dissociative and associative mechanisms.

Scheme 14. Deuterium distribution expected from the Horiuti Polanyi mechanism.

Fig. 23. Changes in deuterium distribution during deuteration of butadiene on MoS2 at room temperature (52) (a) butadiene, (b) 1-butene, (c) hydrogen.

Further important data concerning the reactivities of light and deuterium-labelled isomers are given in Table 4. Data on the deuterium distribution in the carbonyl compounds formed in the transformations of the isomers of 2-methyl-3-phenyloxirane-[ 2- H J are to be found in Table 5. 

The fractionation factor < LA correspondingly refers to the deuterium distribution between the acid and methanol (< LA = (D/H)LA/(D/H)Me0L). From the expression for the limit ->-l, we obtain... 

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