19136-91-5Relevant articles and documents
Parallel Behavior in Kinetic and NMR Effects: Secondary Deuterium Isotope Effects on the Alkaline Hydrolysis of Esters
Matta, Michael S.,Broadway, Dale E.,Stroot, Michele K.
, p. 4916 - 4918 (2007/10/02)
β-Deuterium secondary kinetic isotope effects (β-D KIEs) on the alkaline hydrolysis of the p-nitrophenyl esters of acetic, propanoic, butanoic, and pentanoic acids in pH 10.70, 0.20 M carbonate buffer at 25 deg C tend to increase with increasing chain length of the esters up to the pentanoate.The β-D KIEs are respectively 0.975 +/- 0.004, 0.960 +/- 0.002, 0.940 +/- 0.001, and 0.948 +/- 0.004.The activation energies of the esterolyses of the isotopically light esters follow a similar pattern, as do the 13C NMR nuclear shieldings in CDCl3 of the isotopically light parent carboxylic acids (20.9, 27.4, 35.9, and 33.8 (ppm)) and 13C NMR one-bond isotope shifts produced by disubstitution of deuterium for hydrogen at the α-carbons of the acids (0.45, 0.55, 0.60, and 0.59 (ppm)).Correlation of nuclear shieldings and isotope shifts is known from previous work.The possibility is considered that all of the kinetics-based and NMR relationships are linked through the operation of a common ground-state feature of the ester and acid alkyl chains.
ESR, Structure, and reactions of Specifically Deuterium-Labeled Pentane Cations in X-Irradiated Freon Matrices
Dolivo, G.,Lund, A.
, p. 3977 - 3984 (2007/10/02)
Solutions of 1-2 mol percent of pentane, pentane-3-d2, pentane-2,4-d4, and pentane-1,5-d6 in CFCl3, CF3CCl3, and CF2ClClFCl2 have been X irradiated at 77 K.ESR spectra of the molecular ions were recorded at temperatures between 77 K and either the glass transition temperature for CF3CCl3 (140 K) and CF2ClClFCl2 (about 110 K) or the melting point for CFCl3 (162 K).It was found that the pentane molecular ions in these matrices have not only the structure of an extended chain, but also that of several gauche conformers.Their identity and proportions depend on the matrix and on the labeling.INDO calculations were made to elucidate the detailed structure of the conformers of the pentane molecular ions in these matrices.Tilting both methyl groups toward the central-CH2- leads to a significant decrease in the energy of the ion with a minimum at about 90 deg and to significant changes in hyperfine coupling constants, giving a much better agreement with experimental data.Isotope effects were discovered for the deprotonation reaction in CF2ClCFCl2 and especially for the photofragmentation in CF3CCl3.
The Synthesis of Specifically and Selectively Deuteriated 4,4'-Bisalkoxyazoxybenzene Derivatives
Boden, Neville,Bushby, Richard J.,Clark, Leslie D.
, p. 543 - 551 (2007/10/02)
In connection with deuterium n.m.r. studies of molecular motion in liquid crystals we have developed a number of methods for the synthesis of selectively deuteriated 4,4'-bisalkoxyazoxybenzenes.This paper is concerned with (i) the labelling of specific methylene segments of the alkoxy-chains, (ii) the labelling of the aromatic nucleus, and (iii) the selective enrichment of the deuterium content of one alkoxy-chain relative to the other.Our studies of the n.m.r. spectra of these liquid crystals have shown that there is not (as has sometimes been supposed) a monotonic decrease in C-D quadrupole splitting in passing from the oxygen to the CD3 end of the alkoxy-chain.In -PAA (p-azoxyanisole) we have also shown that the smaller splitting is associated with the CD3O group nearest to the NO end of azoxy-group.Whereas the photorearrangement of azoxy-compounds is normally regiospecific, the photorearrangement of PAA selectively deuteriated in one methoxy-group is unusual in that it leads to isotopically scrambled products.
