Table 1.

Energetic characteristics of the cation conformers of N-AcPro calculated at the B3LYP/6-31++G** level. ΔE and ΔG stand for the relative electronic energy and free energy, respectively, calculated with respect to the cat-endo-ct-d structure (the lowest energy conformer); all values given in kcal/mol.

acetyl and carboxyl groups conformations	ring conformation
	endo		exo
	ΔE	ΔG	ΔE	ΔG
cc-up	5.36	5.45	5.50	5.75
cc-d	2.22	2.80	1.94	2.34
ct-up	3.62	3.56	3.71	3.73
ct-d	0.00	0.00	−0.13	0.15
tc-up	10.63	10.00	11.26	10.66
tc-d	7.42	6.68	7.87	7.29
tt-up	7.54	7.63	6.86	6.65
tt-d	2.33	2.61	3.16	3.49