Enthalpy of formation of the cyclopentadienyl radical: photoacoustic calorimetry and ab initio studies.
The gas-phase C-H bond dissociation enthalpy (BDE) in 1,3-cyclopentadiene has been determined by time-resolved photoacoustic calorimetry (TR-PAC) as 358 +/- 7 kJ mol(-1). Theoretical results from ab initio complete basis-set approaches, including the composite CBS-Q and CBS-QB3 procedures, and basis-set extrapolated coupled-cluster calculations (CCSD(T)) are reported. The CCSD(T) prediction for the C-H BDE of 1,3-cyclopentadiene (353.3 kJ mol(-1)) is in good agreement with the TR-PAC result. On the basis of the experimental and the theoretical values obtained, we recommend 355 +/- 8 kJ mol(-1) for the C-H BDE of 1,3-cyclopentadiene and 271 +/- 8 kJ mol(-1) for the enthalpy of formation of cyclopentadienyl radical.
Nunes
Paulo M
PM
Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal. panunes@fc.ul.pt
Agapito
Filipe
F
Costa Cabral
Benedito J
BJ
Borges dos Santos
Rui M
RM
Martinho Simões
José A
JA
D002151:Calorimetry / Q000295:instrumentation / Q000379:methods; D003517:Cyclopentanes / Q000138:chemical synthesis / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D005740:Gases / Q000737:chemistry; D010782:Photolysis; D011789:Quantum Theory; D013816:Thermodynamics
D003517:Cyclopentanes; D005609:Free Radicals; D005740:Gases; C004709:1,3-cyclopentadiene