Activated Sterically Strained C=N Bond in N-Substituted p-Quinone Mono- and Diimines: XVI. Structural Characteristics

N-Substituted 1,4-quinone imines with an activated sterically hindered C=N bond characteristically react with nucleophiles via 1,2-addition to that bond with formation of quinolide compounds. The C=N–X bond angle in these quinone imines ranges from 130 to 145°, the upper limit being defined by their thermodynamic stability. According to the X-ray diffraction data, the real C=N–X can be smaller than 130°C, but in this case considerable deviations of the nitrogen atom and substituent attached thereto from the mean-square plane of the quinoid ring and twisting of the C=N bond are observed.