Characterization of the unimolecular water elimination reaction from 1-propanol, 3,3,3-propan-1-ol-d3, 3,3,3-trifluoropropan-1-ol, and 3-chloropropan-1-ol.
The unimolecular reactions of 1-propanol, 3,3,3-propan-1-ol-d3, 3,3,3-trifluoropropan-1-ol, and 3-chloropropan-1-ol have been studied by the chemical activation technique. The recombination of CH3, CD3, CF3, and CH2Cl radicals with CH2CH2OH radicals at room temperature was used to generate vibrationally excited CH3CH2CH2OH, CD3CH2CH2OH, CF3CH2CH2OH, and CH2ClCH2CH2OH molecules. The principal unimolecular reaction for propanol and propanol-d3 with 90 kcal mol(-1) of vibrational energy is 1,2-H2O elimination with rate constants of 3.4 x 10(5) and 1.4 x 10(5) s(-1), respectively. For CH2ClCH2CH2OH also with 90 kcal mol(-1) of energy, 2,3-HCl elimination with a rate constant of 3.0 x 10(7) s(-1) is more important than 1,2-H2O elimination; the branching fractions are 0.95 and 0.05. For CF3CH2CH2OH with an energy of 102 kcal mol(-1), 1,2-H2O elimination has a rate constant of 7.9 x 10(5) and 2,3-HF elimination has a rate constant of 2.6 x 10(5) s(-1). Density functional theory was used to obtain models for the molecules and their transition states. The frequencies and moments of inertia from these models were used to calculate RRKM rate constants, which were used to assign threshold energies by comparing calculated and experimental rate constants. This comparison gives the threshold energy for H2O elimination from 1-propanol as 64 kcal mol(-1). The threshold energies for 1,2-H2O and 2,3-HCl elimination from CH2ClCH2CH2OH were 59 and 54 kcal mol(-1), respectively. The threshold energies for H2O and HF elimination from CF3CH2CH2OH are 62 and 70 kcal mol(-1), respectively. The structures of the transition states for elimination of HF, HCl, and H2O are compared.
Ferguson
Heather A
HA
Department of Chemistry, Lyon College, Batesville, Arkansas 72501, USA.
Parworth
Caroline L
CL
Holloway
Traci Berry
TB
Midgett
Aaron G
AG
Heard
George L
GL
Setser
D W
DW
Holmes
Bert E
BE