27853-26-5Relevant academic research and scientific papers
Nitrogen and deuterium kinetic isotope effects on the menshutkin reaction
Szylhabel-Godala,Madhavan,Rudzinski,O'Leary,Paneth
, p. 35 - 40 (1996)
Nitrogen and deuterium kinetic isotope effects were measured in the Menshutkin reaction between methyl iodide and a series of para-substituted N,N-dimethylanilines in ethanol. The nitrogen kinetic isotope effect increases for the more electron-donating substituents [0·9989, 1·0032, and 1·0036 for 4-C(O)Me, II and 4-Me, respectively], in agreement with the Hammond postulate. The secondary deuterium isotope effect, however, exhibits the reverse trend (1·045, 0·989, 0·975 per deuterium, for the respective substituents). This discrepancy is rationalized in terms of solvent molecule participation in the transition state.
Hemiacetals of Acetophenone. Aromatic Substituent Effects in the H+- and General-base-catalysed Decomposition in Aqueous Solution
McClelland, Robert A.,Engell, Karen M.,Larsen, Truels S.,Soerensen, Poul E.
, p. 2199 - 2206 (2007/10/02)
We describe a double-mixing stopped-flow technique for the study of the acid- and base-catalysed breakdown of the unstable methyl hemiacetals of aryl-substituted acetophenones in aqueous solution.The approach takes advantage of the build-up of the hemiacetal during the H+-catalysed decomposition of the corresponding dimethyl acetal.Thus, mixing a weakly basic solution of acetal with excess acid provides a solution containing unchanged acetal, the acetophenone product of the hydrolysis and the hemiacetal intermediate.After a short period of time ( +-catalysed acetal and hemiacetal breakdown are in good agreement with literature data, but our analysis suggests a larger resonance effect component than previously assumed.The corresponding set of Hammett plots for base catalysis of hemiacetal breakdown reveals a relatively weak dependence of the catalytic constants on aromatic substitution, which appears to be inconsistent with much stronger dependences on substitution in the leaving alcohol.We propose a case of non-perfect synchronization or imbalance in the transition state where, in the breakdown direction in a class n mechanism, the degree of C-O bond breakage as measured by β1g is considerable, but the change in hybridization of the central carbon (sp3 -> sp2), as measured by ρ, lags behind in the transition state so that there is less interaction with the aromatic substituents here.
