Substituent Effect in the Ionization of<i>cis</i>-2-Substituted 1-Cyclopropanecarboxylic Acids
作者:Yoshiaki Kusuyama
DOI:10.1246/bcsj.52.1944
日期:1979.7
Ten cis-2-substituted 1-cyclopropanecarboxylic acids (substituents: H, CH3, C6H5, CH3O, C2H5O, Cl, Br, CH3CO, CH3OCO, and C2H5OCO) were prepared, and their pKa values were determined in water at 25 °C, along with those of the trans-2-chloro and 2-methoxy derivatives. The pKa values for cis isomers are somewhat larger than those for the corresponding trans isomers, except for the chloro and bromo derivatives. The substituent effects obtained were in the usual order in the sense of the electronic effects, except for the phenyl group, which produced a decrease in acidity relative to the unsubstituted acid. It was shown that the carbon-13 chemical shifts for the methylene carbon of the ethyl group in the ethyl cis-2-substituted 1-cyclopropanecarboxylate obtained in deuteriochloroform gave a reasonable linear relation with the pKa(cis) values.
合成了十种顺式-2-取代的1-环丙烷羧酸(取代基:H、CH3、C6H5、CH3O、C2H5O、Cl、Br、CH3CO、CH3OCO和C2H5OCO),并在25°C的水中测定了它们的pKa值,以及对应的反式-2-氯和2-甲氧基衍生物的pKa值。顺式异构体的pKa值普遍高于相应的反式异构体,氯和溴衍生物除外。得到的取代基效应与电子效应的通常顺序一致,除了苯基,苯基相对未取代酸表现出酸性下降。研究表明,在去氘氯仿中获得的乙基顺式-2-取代1-环丙烷羧酸酯的亚甲基碳的碳-13化学位移与pKa(cis)值之间存在合理的线性关系。