Activated sterically strained C=N bond in N-arylsulfonyl-p-quinonemono- and diimines: VII. H-1 and C-13 NMR spectra of N-arylsulfonyl-p-benzoquinonemono and diimines

In the N-arylsulfonyl-2,3,5.6-tetrachloro-1,4-benzoquinonemono- and diimine s and in the N-arylsulfonyl-3,5-dimethyl-1,4-benzoquinonemonoimines the inv ersion around C=N bond occurs with high rate due to increased bond angle C= N-S, i.e. to the presence of a sterically strained C=N bond. In the N-aryls ulfonyl-2,6-dimethyl-1,4-quinonemonoimines where the C=N bond is not steric ally strained occurs degenerate Z,E-isomerization, 5-Methoxy-N-phenylsulfon yl-3-chloro-1,4-benzoquinonimine with no sterically strained C=N bond due t o the free rotation of the methoxy group exists in solution as E-isomer wit h respect to chlorine.