H. Takeuchi, M. Sato, T. Tsuji
Aug 10, 1999
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Journal
Journal of Molecular Structure
Abstract
Abstract The molecular structure of benzamide was determined at 445 K by gas electron diffraction. The following structural parameters were obtained ( r g (A) and ∠ α (°)): r (C–C( O))=1.511(5), 〈 r (C–C ring )〉=1.401(2), r (C O)=1.225(3), r (C–N)=1.380(11), 〈 r (C–H)〉=1.112(7), ∠CCC ring =120.0(assumed), ∠CCO=121.2(17), ∠CCN=117.8(16), ∠C cis CC( O)=118.2(17), ∠CCH ring =120.0(assumed), φ (C cis CCO)=19(5) (the C cis atom is cis to the oxygen atom). Numbers in parenthesis are the estimated limits of error (3 σ ) and the angular bracket denotes average values. The steric effect of the amino group was observed in r (C–C( O)), ∠C cis CC( O) and φ (C cis CCO). The C O bond is 0.02 A shorter than that in the crystal and the C–N bond is 0.04 A longer than that in the crystal. These differences are close to the corresponding differences found for formamide and acetamide. RHF/6-31G** calculations were performed on a benzamide dimer to investigate the effect of hydrogen bonding on the geometry. The result shows that the calculated difference between the C O bond lengths of the monomer and dimer is close to half the experimental difference between the gas-phase and solid-phase values. The same conclusion can be drawn for the C–N bond lengths.