90405-66-6Relevant academic research and scientific papers
Factors influencing Kinetic Isotope Effects in Some Proton-transfer Reactions in Aprotic Solvents
Pruszynski, Przemyslaw,Jarczewski, Arnold
, p. 1117 - 1120 (1986)
Kinetic studies have been carried out on the proton-transfer reactions of (i) 4-nitrobenzyl cyanide (4-NBC) with tetramethylguanidine (TMG) and (ii) 4-nitrophenylphenylcyanomethane (4-NPPCM) with 1,8-bis(dimethylamino)naphthalene (DMAN) in acetonitrile.The reaction (i) has a moderate enthalpy of activation (ΔH++ = 25 kJmol-1) and a negative entropy of activation (ΔS++ = -98 Jmol-1K-1).The deuterium kinetic isotope effect is large.The reaction (ii) of the more hindered molecule 4-NPPCM and DMAN has similar activation parameters (ΔH++ = 26 kJmol-1, ΔS++ = -140 Jmol-1K-1), but the kinetic isotope effect is considerably larger; also ΔHD++ - ΔHH++ is larger (13 kJmol-1) and AH/AD is small, indicating a considerable tunnelling effect.Evidence that the larger isotope effect are not artefacts of hydrogen exchange is presented.The tunnelling factor is estimated.
