K. Aarset, K. Hagen
Dec 15, 2008
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Journal
Journal of Molecular Structure
Abstract
Abstract The structure and conformation of phenylacetyl chloride, PhCH 2 (C O)Cl, has been determined by gas-phase electron diffraction (GED), using results from ab initio calculations (HF and MP2/6-311 + G(d,p)) to obtain restraints on some of the structural parameters. The molecules exist in the gas-phase (118 °C) as a mixture of two stable conformers; syn with C O eclipsing C alkyl C phenyl and gauche with C O eclipsing C H. For both conformers the phenyl ring is about 90–120° out of the plane of the acetyl group. The experimentally observed conformational composition was 75(8)% gauche and 25(8)% syn (parenthesised values are 2 σ ). Using theoretical values for the entropy difference between conformers, including the fact that there are two identical gauche forms, this composition corresponds to an enthalpy difference of ΔH°(gauche–syn) = −0.8(12) kJ mol −1 . The results for the principal distances ( r a ) and angles (∠ h 1 ) for the gauche conformer obtained from the combined GED/ ab initio study (2 σ uncertainties) are: r (C H) phenyl = 1.078(6) A, r (C H) alkyl = 1.089(12) A, r (C O) = 1.180(6) A, r (C C) phenyl = 1.396(4) A (average value), r (C phenyl C alkyl ) = 1.509(16) A, r (C alkyl C carbonyl ) = 1.513(12) A, r (C Cl) = 1.780 (6) A, ∠C phenyl C alkyl C carbonyl = 110.6(12)°, ∠C C O = 125.5(8)°, ∠C C Cl = 113.3(6)°, ∠C C H phenyl = 119.9(2)° (average value), ∠C phenyl C alkyl H = 110.8(2)° (average value), ϕ (C C C C) = 118(4)°, ϕ (C C C O) = 95(2)°.