Photoelectron Spectroscopy of the Allenyl Ion CH2=C=CH-

Article abstract of DOI:10.1021/ja00348a008

We have studied the photodetachment spectra of CH2=C=CH^-, CD2=C=CH^-, and CH2=C=CD^-.By comparing the photoelectron spectra of these selectivity labeled species, we conclude that the ion has an allenyl (rather than propargyl) structure.The electron affinities (EA) of a set of propargyl radicals are as follows: EA(CH2C=*CH)= 0.893 +/- 0.025 eV, EA(CD2C=*CH) = 0.907 +/- 0.023 eV, and EA(CH2C=*CD) = 0.88 +/- 0.15 eV.A single active vibration is observed in the photoelectron spectra of CH2=C=CH^- and CD2=C=CH^-.This mode has a frequency of 510 cm^-1 and is assigned as an out-of-plane bend of the acetylenic hydrogen of the propargyl radical (either CH2C=*CH or CD2C=*CH).The gas-phase acidity of allene and methylacetylene are reported as ΔH⁰_acid(H-CH2CCH) = 382.3 +/- 1.2 kcal/mol and ΔH⁰_acid(H-CH=C=CH2) = 380.7 +/- 1.2 kcal/mol.The ΔH_f⁰₂₉₈(CH2=C=CH^-) is 59.4 +/- 1.2 kcal/mol.