SELECTIVITY OF PROTON ABSTRACTION FROM PROPYNE ON THE AG(110) SURFACE

Propyne reacts with oxygen atoms adsorbed on the Ag(110) surface via proton transfer to produce water. At 200 K this reaction is selective toward formation of stable surface methyl acetylides. At 300 K proton abstraction from the methyl group of propyne competes with methyl acetylide formation. Surface methyl acetylides were thermally stable to 500 K; surface propargyl species were unstable and could not be isolated before decomposing to deposit surface carbon. The activation energy difference for proton abstraction from the two ends of propyne was determined to be 3.2 kcal/mol based on results from XPS and TPD experiments. This difference is in good agreement with the calculated stabilities for methyl acetylide and propargyl anions and with the relative rates of proton abstraction in the gas phase. XPS spectra for adsorbed methyl acetylide species demonstrate greater polarization of the acetylenic -orbitals than for adsorbed HC2 species; these results support previous polarization models for alkyl substituent effects on gas-phase acidities. 1985 American Chemical Society.

SELECTIVITY OF PROTON ABSTRACTION FROM PROPYNE ON THE AG(110) SURFACE Academic Article