Bond energy (kJ mol⁻¹) of imides and proton bonded at a, b and c and of the N–C bonded at position 1 (E₁, E_a1, E_b1, E_c1) calculated by Spartan 16 software^a.

position	1a	1b	2e	5d	9
E 1	764.92	774.95	678.95	731.28	770.14
E a1	148.35	168.29	86.81	108.23	99.55
E b1	115.22	97.53	11.76	38.21	84.98
E c1	139.98	124.70	39.36	67.22	112.60

^aa, b and c: bonding sites for hydrogens (Fig. 4).