Deuterium substitution interpretation

The influence of deuterium substitution on the acid base effects in hydrogen bonds has been considered [3], The treatment given here has been designed to enable a more quantitative consideration of these effects to be made and to interpret the known contraction phenomena. 

TTie dielectric behaviour of the deuterium substituted crystal has also been studied. The Tc is drastically raised to about 500 K. This large isotope effect supports the interpretation that the dielectric response of squaric acid is derived from proton (deuterium) tautomerism. Similar isotope effects on... 

Examples of current work are given starting with relatively simple systems such as liquids composed of homo-nuclear diatomic molecules (N2,02,CJl2>Br2 etc). Other types of molecular species are presented with illustrative examples of the way in which the experimental observations may be interpreted. The use of isotopic substitution in neutron diffraction measurements is described and the special case of hydrogen/deuterium substitution is briefly treated. The particular case of liquids which exhibit strong hydrogen-bonding is discussed in relation to temperature variation studies of water. 

Substituting deuterium for hydrogen gas in the reduction of BT to DHBT with the catalyst precursor [Rh(NCMe)3(Cp )](BF4)2 has shown that the stereoselective ds-deuteration of the double bond is kinetically controlled by the tj2-C,C coordination of BT. The incorporation of deuterium in the 2- and 3-positions of unreacted substrate and in the 7-position of DHBT has been interpreted in terms of reversible double-bond reduction and arene-ring activation, respectively (Scheme 16.14) [55]. 

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. 

It has been shown that the interpretation of catalytic reactions involving group VIII transition metals in terms of n complex adsorption possesses considerable advantages over classical theories by providing a link between theoretical parameters and chemical properties of aromatic reagents and catalysts. The concept has led to the formulation of a number of reaction mechanisms. In heavy water exchange the dissociative tt complex substitution mechanism appears to predominate it could also play a major role when deuterium gas is used as the second reagent. The dissociative mechanism resolves the main difficulties of the classical associative and dissociative theories, in particular the occurrence... 

The 100 MHz H-NMR spectrum of polypropylene oxide is too complex to be analyzed accurately even when decoupled from methyl protons. It is reasonable to ascribe the complexity of the spectrum to the spin coupling between hydrogen atoms linked to contiguous carbon atoms in the main chain. If this interpretation is correct, the spectrum should be simplified by substituting the methine proton by a deuterium atom. In fact, the spectrum of polypropylene oxide-a-d was simpler than that of the undeuterated one. Methyl protons lie at higher field and methylene protons at lower field. The stereoregularity was analyzed on the basis of the spectrum of the methylene proton absorption other than that of the methyl proton absorption. 

The a-secondary IE of two deuteriums on the rate of base-catalyzed CD exchange of toluene, 3A ( PhC112D)/k(PhCD is 1.31, and the [3-secondary D IE on the rate of base-catalyzed a-C-D exchange of ethylbenzene, k(PhCHDCH3)//t(PhCHDCD3), is 1.11 0.03.58 Similarly, from the rates of base-catalyzed a-C-D exchange of tolucne-a,4-r/2, -a,2,4,6-c/4, and -a,2,3,4,5,6-d6 and with an assumption of linearity of IEs, the contributions of ortho, meta, and para deuteration lead to rate retardations of 2.4, 0.4, and 1.8%, respectively.59 These are all kinetic IEs, but to the extent that the transition state resembles closely the carbanion, or to the extent that the reverse reprotonation is encounter-controlled and independent of isotopic substitution, these kinetic IEs represent equilibrium IEs on acidity. The IEs were interpreted in terms of an electron-donating inductive effect of D relative to H. 

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