Two series of para disubstituted benzenes were studied: 2-(4-X-phenyl)-1,3-dihydro- 2H-isoindole-1,3-diones (1) and 3-(4-X-phenyl)-3,4-dihydro-2H-1,3-benzoxazine-2,4-diones (2). Their 1H and 13C chemical shifts were correlated with substituent shift increments (SSI) aj and zj, respectively. For 13C chemical shifts, all four zj values, zi, zo, zm, and zp, were used to check the assignment and to find out possible variables for improvement of regression equations. Significant deviations from plain additivity were observed in the case of δH3 and δC3 chemical shifts. This can be explained by changes in diamagnetic anisotropy contribution induced by different twist of 4-substituent from the benzene plane caused by variable substituent in position 1.
研究了两组
para二取代苯:2-(4-X-苯基)-1,3-二氢-2
H-异
吲哚-1,3-二酮(
1)和3-(4-X-苯基)-3,4-二氢-2
H-1,3-苯并噁嗪-2,4-二酮(
2)。它们的
1H和
13C
化学位移与取代基位移增量(SSl)
aj和
zj相关。对于
13C
化学位移,所有四个
zj值,
zi,
zo,
zm和
zp,都被用来检查分配并找出可能改进回归方程的变量。在δ
H3和δ
C3化学位移的情况下观察到明显的偏离简单加性。这可以通过由位于位置1的可变取代基引起的苯环平面外4-取代基的不同扭曲引起的抗磁性异向贡献的变化来解释。