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Table 5 Geometric parameters for N–H···O=C bonds

From: Specific energy contributions from competing hydrogen-bonded structures in six polymorphs of phenobarbital

D-H···A

d(D-H)/Ã…

d(H···A)/Å

d(D···A)/Å

∠(DHA)/°

Pbtl-V (C-3)

 (a) N1–H1···O4

0.88(2)

1.92(2)

2.772(5)

164(5)

 (b) N3–H3···O2′ii

0.878(19)

1.91(2)

2.790(5)

177(5)

 (c) N1′–H1′···O4′iii

0.87(2)

2.00(2)

2.832(5)

160(4)

 (d) N3′–H3′···O2ii

0.903(19)

1.99(2)

2.874 (5)

168(5)

Pbtl-VI (C-5)

 (a) N1–H1···O4i

0.887(14)

2.108(15)

2.974(2)

165.2(18)

 (b) N3–H3···O2′

0.887(15)

1.966(15)

2.838(2)

167.3(19)

 (c) N1′–H1′···O4

0.898(15)

2.052(16)

2.936(2)

168.0(17)

 (d) N3′–H3′···O2v

0.892(15)

1.969(16)

2.852(2)

170.7(19)

  1. Symmetry transformations: (i) x, y + 1, z; (ii) 1 âˆ’ x, 1 âˆ’ y, 2 âˆ’ z; (iii) x, y âˆ’ 1, z; (iv) 1 âˆ’ x, 2 âˆ’ y, 2 −z; (v) −x + 3/2, y âˆ’ Â½, −z + Â½