Singlet methylcarbene: Equilibrium geometry or transition state
- Univ. of Georgia, Athens, GA (United States)
The isomerization of singlet methylcarbene to ethylene has been studied using ab initio quantum mechanical methods, resulting in high-level theoretical predictions of the transition-state structure and isomerization barrier height. Basis sets as large as triple-[zeta] plus double polarization plus carbon atom f and hydrogen atom d functions [TZ2P(f,d)] have been used with the self-consistent-field (SCF) configuration interaction, including all single and double excitations (CISD), and coupled cluster, including all single and double substitution (CCSD) methods, as well as CCSD with the effects of connected triple excitations added perturbatively [CCSD(T)]. The geometries for ground-state singlet methylcarbene and the transition state are both of C[sub 1] symmetry. The classical barrier is predicted to be 2.0 kcal mol[sup [minus]1], while the activation energy ([Delta]E[sub 0]) is 1.2 kcal mol[sup [minus]1] at the TZ2P(f,d) CCSD(T) level at 0 K; and the free energy barrier is [Delta]G[sup 0] = 1.5 kcal mol[sup [minus]1] at 298 K. The activation energy is 0.3 kcal mol[sup [minus]1] higher for fully deuterated singlet methylcarbene. Therefore singlet methylcarbene appears to be a true intermediate, consistent with some experimental deductions. 18 refs., 1 fig., 5 tabs.
- DOE Contract Number:
- FG09-87ER13811
- OSTI ID:
- 7267280
- Journal Information:
- Journal of the American Chemical Society; (United States), Journal Name: Journal of the American Chemical Society; (United States) Vol. 116:8; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
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71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ACTIVATION ENERGY
ALKENES
CARBENES
CHEMICAL REACTIONS
COMPILED DATA
DATA
ENERGY
ENERGY LEVELS
ENTHALPY
ENTROPY
ETHYLENE
EXCITED STATES
FREE ENERGY
HYDROCARBONS
INFORMATION
ISOMERIZATION
MECHANICS
NUMERICAL DATA
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
QUANTUM MECHANICS
RADICALS
REACTION INTERMEDIATES
THERMODYNAMIC PROPERTIES
VIBRATIONAL STATES