Table 1. Computed Relative Energies (kcal/mol) of Tautomers/Conformers of Neutral and Singly Protonated 1.

	gas		water
tautomer	s-cis	s-trans	s-cis	s-trans
1H	6.7	6.3	0.4	0.0
2H	0.0	9.2	0.5	1.3
4H	18.2	6.4	5.2	3.5
1H–1′H	0.4	0.0	0.5	0.0
2H–1′H	3.6	not stablea	3.0	7.1
4H–1′H	23.2	7.2	7.6	5.0
1H–4H	18.2	13.8	6.1	7.8

^aInterconverts in the conformer s-cis upon geometry optimization.