Table 4.

Intramolecular H-bonds parameters for the preferred conformations of 3a′ and 5a.

compound (conformation)	C3–C = O, C5C = O orientation	energy, kcal mol−1 (kJ mol−1)	d, Å (α,°) NH⋯O = C	d, Å (α,°) NH⋯–O–	d, Å (α,°) CH⋯O = C	d, Å (α,°) CH⋯–O–
3a′ (A)	s-cis, s-cis	0.00 (0.00)	2.035 (141.3)		2.149 (123.4)
3a′ (B)	s-trans, s-cis	0.68 (2.85)	2.053 (140.1)			2.170 (115.8)
3a′ (C)	s-trans, s-trans	1.48 (6.19)	2.065 (139.9)			2.172 (115.8)
3a′ (D)	s-cis, s-cis	0.72 (3.01)		2.042 (109.0)	2.512 (88.8)
					2.471 (91.0)
3a′ (E)	s-trans, s-cis	1.39 (5.82)		2.031 (109.5)		2.446 (88.4)
						2.426 (89.4)
3a′ (F)	s-trans,s-trans	2.31 (9.67)		2.034 (109.5)		2.482 (86.8)
						2.408 (90.7)
5a (A)	s-cis, s-cis	0.00 (0.00)	2.163 (130.9)		2.183 (119.2)
			2.306 (119.7)		2.177 (120.9)
5a (B)	s-cis, s-trans	0.45 (1.88)	2.195 (128.9)		2.182 (119.3)	2.194 (112.8)
			2.289 (120.8)
5a (C)	s-trans, s-trans	1.09 (4.56)	2.171 (130.5)			2.193 (111.3)
			2.420 (113.7)			2.200 (113.2)
5a (D)	s-cis, s-cis	8.32 (34.81)		2.058 (107.2)	2.464 (90.8)
					2.469 (90.6)
				2.058 (107.2)	2.501 (89.0)
					2.437 (92.3)
5a (E)	s-cis, s-trans	9.32 (38.99)		2.062 (107.3)	2.468 (90.7)	2.472 (86.6)
				2.058 (107.2)	2.468 (90.7)	2.363 (92.4)
5a (F)	s-trans, s-trans	10.46 (43.76)		2.044 (107.9)		2.410 (89.5)
						2.408 (89.6)
				2.045 (107.8)		2.442 (88.0)
						2.387 (91.0)