天然丰度氘核磁共振测定一级和二级动力学氘同位素效应(Ⅱ)——外标的分子内和分子间竞争法

Simultaneous Measurement of Primary and Secondary Kinetic Deuterium Isotope Effects by Natural-Abundance~2HNMR(Ⅱ)——Inter-and Intramolecular Competition Using External Reference

建立了用外标的天然丰度^(2)H NMR同时测定一级和不同类型二级动力学同位素效应的方法。用此法测定了苯氯化和溴化,甲苯氯化以及苯甲醇氧化等反应的同位素效应值。

A novel method for simultaneous measurement of primary and secondary kinetic deuterium isotope effects(KDIEs’)by natural-abundance^(2)H NMR using external reference was established.The method takes into account both inter-and intramolecular competitions.Generalized equations used in internal as well as external reference methods are given.is primary is the secondary KDIE of deuterium which is chemically equivalent to the lost hydrogen and remains after the reaction while kH/kdD,Ⅱis the secondary KDIE of deuterium that,is not situated in the reaction center,i.e.that has no chance to be lost,n is the number of chemically equivalent hydrogen atoms involved in bond breaking in the reaction center of the substrate molecule.F refers to the mole fraction of the remaining fully protonated substrate after reaction.A and B are signal intensity ratios of deuterium at the reaction center of the starting and remaining reagents to that of the(internal or external)reference,respectively.C is the signal intensity ratio of deuterium of the residual hydrogen site after reaction in the pro-duct to that of the reference.When external referece is used,C must be corrected with a factor J=dRMP/dPMR where d and M refer to density and molecular weight of the sample and subscripts R and P denote reactant and product,respectively.M and N are signal intensity ratios of deuterium which induces secondary KDIE and situates outside the reaction center of the starting and remaining reagent molecules to that of the reference,respectively.The established method was applied to the KDIE study of some reactions.The kH/kD,Ⅰvalue of chlorination of benzene catalysed by AgClO4(25℃)was 0.89 and its kH/kD,Ⅱvalue was 1.01.For the bromination of benzene under the same conditions as its chlorination,in assuming kH/kD,Ⅱ=1,kH/kD,Ⅰ=0.99.For the chlorination of toluene(103℃)kH/kD,Ⅰ=l.78,kH/kD,Ⅱ=0.96,kH/kD’,Ⅱ=1.01 and for the oxidation of benzyl alcohol by CrO3 to benzaldehyde(42℃)kH/kD,Ⅰ=7.63,kH/kD,Ⅱ=1.20,kH/kD’,Ⅱ=1.00.