13C NMR Spectra of the dianions Li2-n resulting from double deprotonation of unsaturated carboxylicacids 1 to 6 by lithium dialkylamides, are examined. Higher field resonance for C2 than for C4 atoms are observed, which reveal higher elctron density at C2 than at C4, in agreement with the kinetic α-regioselectivity exhibited by these dianions on reaction with electrophiles.
考察了由不饱和羧酸1至6被二烷基酰胺锂双重去质子化后的二价阴离子Li 2 -n的13 C NMR光谱。观察到C 2的原子共振高于C 4原子,这表明C 2的电子密度高于C 4的电子,这与这些二价阴离子与亲电子试剂反应所表现出的动力学α-区域选择性一致。