Schematic models of TS_R(H) and TS_S(H) and the summary of hydrogen bonding interactions.

Hydrogen bond	L: length (Å), A: angle (°), E: energy (kcal mol−1)	TSR(H)	TSS(H)
N1⋯H1⋯O1	L (H1–O1)	1.65	1.65
	A (N1–H1–O1)	169	171
	E (H1–O1)	13.3	12.8
N2⋯H2⋯O2	L (H2–O2)	1.75	2.16
	A (N2–H2–O2)	167	123
	E (H2–O2)	10.4	1.3
C1–H3⋯O2	L (H3–O2)	2.60	—
	A (C1–H3–O2)	167	—
	E (H3–O2)	0.8	—
C2–H4⋯O2	L (H4–O2)	—	2.19
	A (C2–H4–O2)	—	123
	E (H4–O2)	—	2.4
C–H5⋯C3	L (H5–C3)	—	2.82