Table 3.

Comparison of H-bond parameters in model compounds 1f, 1b and 2b, 2f and 3b.

Compound	C2(CH···O)	C6(CH···O)	C2 pyr(CH···O)	C6 pyr(CH···O)
1f	2.508 Å,	2.511 Å,	-	-
	(86.6°)	(86.5°)
	2.376 Å,	2.374 Å,
	(93.6°)	(93.7°)
1b	2.032 Å,	2.073 Å,	-	-
	(131.5°)	(126.0°)
2f	2.329 Å,	2.168 Å,	2.629 Å,	2.152 Å,
	(99.6°)	(117.7°)	(89.7°)	(137.3°)
2b	2.254 Å,	2.198 Å,	2.544 Å,	2.913 Å,
	(103.9°)	(107.7°)	(94.0°)	(87.5°)
3b	2.341 Å,	2.366 Å,	2.591 Å,	2.849 Å,
	(98.914°)	(96.979°)	(90.362°)	(82.121°)