Hydrogen bonding in aromatic formamides
The solid state structures of two p-substituted aromatic formamides have been determined. p-Nitro formamido benzene (1) crystallizes in the monoclinic space group C2/c with a = 10.9859(7), b = 10.0576(7), c = 13.0331(9) Å, β = 97.148(1)∘ and Z = 8. p-formamido anisole (2) crystallizes in the orthorhombic space group Pna21 with a = 10.5598(7), b = 7.6553(5), c = 9.2522(6) Å and Z = 4. Both compounds show hydrogen bonding in the solid state, forming infinite chains via N–H⋅ < eqid1 > ⋅O = C bridges. For the anisole formamide (2), the molecules exhibit in a zig-zag arrangement. The nitro compound (1) exhibits a spiral-like wavy line with a fourfold repeating unit, making it the first formamide having a chiral N–H⋅ < eqid2 > ⋅O bridged chain reminiscent of those found for α-helices in proteins. While the individual spirals of 1 are orientated either clockwise or counterclockwise, their orientation towards each other is random.
Key wordsFormamides hydrogen bonding disorder infinite chain spiral disorder
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