Modeling the competitive dissociation of protonated 2,3-butanedione. The enthalpy of formation of methylhydroxycarbene.
The enthalpy of formation of methylhydroxycarbene, CH(3)COH, has been determined from measurements of the threshold energy for collision-induced dissociation of protonated 2,3-butanedione in a flowing afterglow-triple quadrupole mass spectrometer and found to be 16 +/- 4 kcal/mol, 57 +/- 4 kcal/mol higher than that of acetaldehyde. From the measured enthalpy of formation, the difference between the first and second C-H BDEs in ethanol is found to be 17 kcal/mol, which implies a singlet-triplet splitting of 28 kcal/mol in the carbene. The activation energies for loss of ketene and carbon monoxide from protonated butanedione are found to be 60 +/- 4 and 50 +/- 4 kcal/mol, respectively. On the basis of experimental and computational results, the loss of carbon monoxide is proposed to proceed through a tight transition state. Although calculations also suggest a tight transition state for loss of ketene, the experimental data indicate that it occurs via a loose transition state, possibly forming by proton transfer along the direct dissociation pathway.
Liu
Xinping
X
The Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393, USA.
Gross
Michael L
ML
Wenthold
Paul G
PG
D003931:Diacetyl / Q000737:chemistry*; D006838:Hydrocarbons / Q000737:chemistry; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D008956:Models, Chemical; D015394:Molecular Structure; D011522:Protons; D013816:Thermodynamics
D006838:Hydrocarbons; D011522:Protons; C030011:carbene; D003931:Diacetyl; D008697:Methane