Formylmethylene: the triplet ground state and the lowest singlet state
Date
2013Author
Guan, Jun
Randall, Katherine R.
Li, Huidong
Schaefer, Henry F. III
Metadata
Show full item recordAbstract
The ground triplet state and lowest singlet state of formylmethylene
have been proposed as important intermediates in the Wolff
rearrangement of α-diazo ketones into ketenes. The ground triplet state of
formylmethylene has been examined experimentally, but the lowest singlet state
has yet to be observed. We predict equilibrium geometries, energies, bonding,
dipole moments, and harmonic vibrational frequencies for these two lowest states
of formylmethylene at the cc-pVQZ CCSD(T) level of theory. The singlet−
triplet energy difference [ΔE(S-T)] is quite sensitive to the level of theory. The
highly accurate cc-pVQZ CCSD(T) level of theory yields the most reliable result
of only 2.0 kcal mol−1. An estimate based on the experimentally characterized
CH2 molecule yields ΔE(S-T) = 1.27 kcal mol−1. In addition, accurate quartic force fields have been determined at the cc-pVTZ
CCSD(T) level of theory. Fundamental vibrational frequencies, anharmonic constants, and vibration−rotation coupling
constants were determined using vibrational second-order perturbation theory (VPT2). Our results should aid in experimental
detection and characterization of the lowest singlet state of formylmethylene, which is highly desirable for better understanding
the mechanism of the Wolff rearrangement.