59660-67-2Relevant academic research and scientific papers
A Correlation between β-Hydrogen Isotope Effects on Carbon-13 NMR Chemical Shifts in Unsaturated Systems and the Strength of Hyperconjugative Interactions
Arrowsmith, Cheryl H.,Kresge, A. Jerry
, p. 7918 - 7920 (1986)
β-Hydrogen isotope effects on the carbon-13 NMR chemical shifts of the trigonal carbon in CL3C(R)=X (L=H, or D) are reported for 15 substances inwhich the positive charge density at the trigonal carbon is regulated through systematic variation of R and X.A linear relationship is found between these isotope effects and the chemical shifts of the trigonal carbons, and this is taken as evidence for dependence of the magnitude of these isotope effects upon the strength of the hyperconjugative interaction between CL3 and C(R)=X.An explanation of hyperconjugative NMR isotope effecs in terms of anharmonic carbon-hydrogen bond-bending vibrations is advanced.
Studies on the Mechanism of the Enolization Reaction of Grignard Reagents and Ketones. Part 2. Pseudo-first-order Rate and Deuterium Isotope Effect Studies
Pinkus, George A.,Sabesan, Arunachalam
, p. 473 - 477 (2007/10/02)
Kinetics of enolization reactions of some alkyl mesityl ketones with alkylmagnesium bromides were studied under pseudo-first-order conditions by measuring formation of gaseous alkane.Using a large fixed excess of isopropyl mesityl ketone, the reaction was first order in ethylmagnesium bromide; with a fixed excess of ethylmagnesium bromide, the reaction was first order in ketone.At high excess variable concentrations of ketone, however, k2 values decreased with increasing ketone concentration in a good linear relation between the two variables.When both Grignard and ketone concentrations (at 1:1 mole ratios) were varied, a nonlinear relationship resulted between concentrations and k2 values.Rates did not vary significantly between highly pure and reagent grade magnesium.Reactions in tetrahydrofuran at b.p. 67 deg C took place at significantly slower rates than reactions in ether at b.p. 36 deg C at comparable concentrations whereas reactions in di-n-butyl ether at b.p. 141 deg C occurred at a much faster rate at higher concentrations.Reactions of α-deuterio-substituted methyl, ethyl, and isopropyl mesityl ketones with ethylmagnesium bromide showed isotope effects confirming breaking of the C-H bond as the rate-determining step in accord with the proposed mechanism.Values of kH/kD=2.6-3.1 indicate a moderate degree of C-H bond stretching in the transition state.A two-step mechanism is proposed.
