Table 2.

Selected bond lengths (Å) and angles (°) in the structures of 1–4, obtained by using the B3LYP/6-311++G(d,p) method ¹.

	1	2	3	4
Bond lengths
C=N	1.2816	1.2821	1.2800	1.2787
C–O(H)	1.3410	1.3448	1.3390	1.3298
C=O	1.2034	1.2036	1.2030	1.2031
C–O(Et)	1.3462	1.3461	1.8529	1.3440
Bond angles
C=N–C	119.04	118.98	119.17	119.43
Dihedral angles 2
N–C–C=O	29.12	−31.15	24.53	21.83
O=C–O–C	1.54	−1.44	1.53	1.46
C–O–C–C	−179.86	179.95	−0.21	179.87
Hydrogen bonds
O–H	0.9927	0.9913	0.9933	0.9985
H∙∙∙N	1.7472	1.7546	1.7464	1.7200
O∙∙∙N	5.6362	2.6395	2.6342	2.6160
∠(O–H∙∙∙N)	147.05	146.66	146.79	147.22

¹ The computational results have been compared according to the crystallographic data [17]. ² The corresponding dihedral angles must be compared by their magnitudes.