Tautomerism of 4-amino- and 4-arylamino-1,2-naphthoquinones.
作者:HIROSHIGE YANO、MIYUKI YAMASAKI、YUKIKO SHIMOMURA、MASATAKE IWASAKI、MUTSUKO OHTA、YOHKO FURUNO、KEIKI KOUNO、YUKIO ONO、YO UEDA
DOI:10.1248/cpb.28.1207
日期:——
The 13C chemical shifts of 4-amino- and 4-arylamino-1, 2-naphthoquinones measured in DMSO-d6, pyridine-d5 and a D2O solution of NaOD indicated that the predominant tautomer in neutral solvents is the 1, 2-dioxo-4-amino-naphthalene (Ia) form, while that in weak basic solvents is the 1-oxo-2-hydroxy-4-imino-naphthalene (Ib) form and that in an aqueous solution of NaOH is the anion of the Ib form. The electronic spectrum of 4-anilino-1, 2-naphthoquinone measured in a mixture of EtOH and 0.05M H3SO4 (1 : 4 by volume) indicated that its tautomeric form in an aqueous strong acid solution is the Ia form and that the compound is hydrolyzed quickly to produce 2-hydroxy-1, 4-naphtho-quinone. The magnitudes of substituent effects observed in the electronic spectra of 4-(4'-substituted)-anilino-1, 2-naphthoquinones measured in EtOH were found to be smaller than those measured in pyridine. This difference was considered to provide confirmation that the predominant tautomer in neutral solvents is the Ia form. The theoretical π-π* transition energies of 4-arylamino-1, 2-naphthoquinones were calculated for both the Ia and the Ib forms by means of Pariser-Parr-Pople type molecular orbital calculations.
在DMSO-d6、吡啶-d5和NaOD的D2O溶液中测得的4-氨基和4-芳氨基-1,2-萘醌的13C化学位移表明,在中性溶剂中,主要互变异构体是1,2-二氧代-4-氨基萘(Ia)形式,而在弱碱性溶剂中,是1-氧代-2-羟基-4-亚氨基萘(Ib)形式,在NaOH水溶液中,是Ib形式的阴离子。在EtOH和0.05M H3SO4(体积比1:4)的混合物中测得的4-苯胺基-1,2-萘醌的电子光谱表明,在水性强酸溶液中,其互变异构形式是Ia形式,并且该化合物迅速水解生成2-羟基-1,4-萘醌。发现在EtOH中测得的4-(4'-取代)苯胺基-1,2-萘醌的电子光谱中的取代基效应的幅度小于在吡啶中测得的。这种差异被认为是证实中性溶剂中主要互变异构体为Ia形式的证据。通过Pariser-Parr-Pople型分子轨道计算,分别计算了4-芳氨基-1,2-萘醌的Ia和Ib形式的理论π-π*跃迁能量。