O− + Acetaldehyde Reaction Products: Search for Singlet Formylmethylene, a Wolff Rearrangement Intermediate

Gas-phase detection of oxirene

Oxirenes-highly strained 4π Hückel antiaromatic organics-have been recognized as key reactive intermediates in the Wolff rearrangement and in interstellar environments. Predicting short lifetimes and tendency toward ring opening, oxirenes are one of the most mysterious classes of organic transients, with the isolation of oxirene (c-C₂H₂O) having remained elusive. Here, we report on the preparation of oxirene in low-temperature methanol-acetaldehyde matrices upon energetic processing through isomerization of ketene (H₂CCO) followed by resonant energy transfer of the internal energy of oxirene to the vibrational modes (hydroxyl stretching and bending, methyl deformation) of methanol. Oxirene was detected upon sublimation in the gas phase exploiting soft photoionization coupled with a reflectron time-of-flight mass spectrometry. These findings advance our fundamental understanding of the chemical bonding and stability of cyclic, strained molecules and afford a versatile strategy for the synthesis of highly ring-strained transients in extreme environments.

Photodetachment anisotropy for mixed s-p states: 8/3 and other fractions

An approximate model for analytical prediction of photoelectron angular distributions in anion photodetachment from mixed s-p states is presented. Considering the dipole-allowed s, p, and d free-electron partial waves, the model describes photodetachment anisotropy in terms of the fractional p character of the initial orbital and the A and B coefficients describing the relative intensities of the p → d to p → s and s → p to p → s channels, respectively. The model represents an extension of the central-potential model to an intermediate regime encompassing varying degrees of s and p contributions to the initial bound orbital. This description is applicable to a broad class of hybrid molecular orbitals, particularly those localized predominantly on a single atom. Under the additional assumption of hydrogenic or Slater-type orbitals, the B/A ratio in photodetachment from a mixed 2s-2p state is shown to equal 8/3. Corresponding fractions are derived for other ns-np mixing cases. The predictions of the model are tested on several anion systems, including NH(2)(-) and CCl(2)(-). The quantitative discrepancies in the latter case are attributed to the breakdown of the central-atom approximation and a mechanism for corresponding corrections is indicated.