The imine C=N bond length at C4 is 1.291 (3) Å , which is shorter than the enamine C—N bond length at C2  [1.353 (3) Å ] reflecting the greater double bond character at C4. The distance between the enamine N/t-butyl C [1.475 (4) Å] is shorter than the imino N/t-butyl C [1.485 (3) Å] due to steric compression at the imine.  However, the bond angles around the two nitrogens [imine C4-N-C(tert-butyl) = 124.1 (2)° versus enamine C2-N-C(tert-butyl) = 129.2 (2)°] are very similar due to the delocalization of pi electrons between the two nitrogens. This system can be considered to be a type of vinylogous amidine, with both nitrogens as trigonal planar. The aromatic ring is planar, as expected, and has internal bond angles that range from 118.6 (2)° to 120.6 (2)°. However, the quinone system is slightly non-planar, with the C3-C4(imine)-C4a angle of 116.9 (2)° showing the greatest deviation from the ideal 120°. 

Supramolecular features

In the crystal structure of (I) (Fig. 7), the center of the unit cell contains the tert-butyl groups. There are no intermolecular hydrogen bonds, as seen in a similar structure with n-butyl groups (vide infra); the tert-butyl groups shield the nitrogen and prevent close approach of the supramolecular donors and acceptors. There are no pi–stacking interactions present; the aromatic rings are separated by more than 6 Å.