π bonded intermediates in alcohol oxidation: Orientations of allyloxy and propargyloxy on Ag(110) by near edge x-ray absorption fine structure

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Abstract
The orientation of allyl alcohol (CH2=CHCH2OH), propargyl alcohol (CH 3/4 CCH2OH), and their surface alkoxy groups has been examined on Ag(110) using near edge x-ray absorption fine structure (NEXAFS) measurements. The planes containing the π* orbitals of allyl alcohol and its alkoxy species, allyloxy (CH2=CHCH2O−), are tilted 26±4° and 32±5° from the surface normal, respectively. Allyl alcohol itself shows no azimuthal ordering, but the π* orbital in allyloxy is azimuthally oriented 33±15° from the close-packed direction ([11̄0] azimuth). Propargyl alcohol is randomly oriented on the Ag(110) surface. Its alkoxy group, propargyloxy (CH 3/4 CCH2O−), is strongly oriented with the triple bond axis parallel to the plane of the surface and directed along the [001] azimuth, perpendicular to the troughs. The position of the σ* resonances indicate that no loss of the allylic hydrogen has occurred and that the double and triple bonds are slightly, but not significantly, perturbed from their normal gas phase bond lengths.