Table 1.

The relative energies (kJ/mol) of four tautomers of compounds 1–11 (Figure 2) calculated at the B3LYP/6-311++G(2df,2pd) level.

	R5	R6	2,3-I (keto)	1,2-I (keto)	2,4-I (enol)	1,3-I (imino) 1
1	H	H	0.0	13.9	20.7	23.3
2	CH3	H	0.0	12.0	30.5	23.8
3	t-butyl	H	0.0	12.8	22.0	22.3
4	NH2	H	0.0	6.5	25.9	29.6
5	CF3	H	0.0	16.3	24.3	28.7
6	NO2	H	0.0	24.9	24.6	34.8
7	H	CH3	0.0	12.6	28.2	21.3
8	H	t-butyl	0.0	12.8	27.8	22.3
9	H	NH2	0.0	34.8	28.0	36.7
10	H	CF3	0.0	32.3	29.0	45.3
11	H	NO2	0.0	32.5	20.0	49.1

¹ The energies of both rotamers of the imino group have been calculated, the lower of which is presented here. The energies of both rotamers are given in the SI.