A Theoretical Study of the Properties and Reactivities of Ketene, Thioketene, and Selenoketene

Abstract

The properties and reactivities of ketene, thioketene, and selenoketene were studied using the G2(MP2) level of theory. Calculated structures, vibrational frequencies, dipole moments, NMR chemical shifts, and charge distributions strongly suggest that thioketene and selenoketene are best represented by the neutral cumulenic form. Four prototype reactions were examined: ketene‐ynol rearrangement, electrophilic and nucleophilic addition, and [2+2] cycloaddition. Thioketene and selenoketene were found to be more reactive than ketene in all reactions. In terms of chemistry, thioketene resembles selenoketene more than ketene. The variation of reactivity can readily be explained in terms of strain energy, electronegativity, and molecular orbital arguments.

Velocity-Map Imaging and Magnetic-Bottle Photoelectron Spectroscopy of [SeCCH]−: Electronic Properties and Spin–Orbit Splitting

“…It was only in 2018 that the main group element selenium was included in their investigations leading to A I SeCCH containing the unprecedented [SeCCH] − anion . This anion was predicted in theoretical work − but has never been seen experimentally before. As it contains an interesting Se–C bond within a small acetylide unit, it seems to be worthwhile to investigate the specific bonding situation in this compound in more detail.…”

Pathways for Concerted [2 + 2] Cycloaddition to Cumulenes

“…Cycloadditions of ethylene to ketene to give cyclobutanone ( 9 ), − to thioketene to give cyclobutanethione ( 10 ), and to methyl isothiocyanate to give thiolactam 11 are shown in Scheme . The corresponding transition states ( TS9 – TS11 ) appear in Figure , where it is clear that the leading new C–C bond is forming nearly in the nodal plane of the CC and CN π bonds of the cumulenes.…”

“…Despite these disclaimers, there are cumulenes in the table for which concerted [2 + 2] cycloadditions have been found and others for which they may be realizable. Ketene, of course, and electronegatively substituted isocyanate fall in the first category; thioketene (predicted to be more reactive than ketene) and perhaps electronegatively substituted carbodiimide are prospects for the second. Though allene and N -methylketenimine have open-shell transition states a little below the concerted ones at the level of theory we have employed, appropriately substituted analogues may not.…”

Untitled

“…Ma and Wong calculated the [2 + 2] cycloadditions of ethene with ketene, thioketene and selenoketene. 31 Additions to the CNC versus CNX moieties of H 2 CNCNX were compared at the G2(MP2) level of theory. All attempts to locate zwitterionic intermediates were unsuccessful.…”