Energetics of tert-butoxyl addition reaction to norbornadiene: a method for estimating the pi-bond strength of a carbon-carbon double bond.
The energetics of tert-butoxyl radical addition reaction to norbornadiene was investigated by time-resolved photoacoustic calorimetry (TR-PAC). The result, together with the C-O bond dissociation enthalpy (BDE) in the addition product, allowed us to calculate the pi-bond dissociation enthalpy in norbornadiene. Quantum chemistry (QC) methods were also used to obtain several enthalpies of reaction of the addition of oxygen-centered radicals to alkenes. The pi-bond dissociation enthalpies in these molecules were calculated by a procedure similar to that used in the case of norbornadiene and were compared with the pi-BDE values obtained by the method proposed by Benson. These two different approaches yield similar values for the pi-BDEs in alkenes, indicating that the addition method proposed in the present study is a valid way to derive that quantity. The influence of strain in the pi-BDEs of cyclic alkenes was investigated and allowed us to justify the difference between the pi-BDE in norbornene and norbornadiene. Finally, the thermochemistry of the addition and abstraction reactions involving these two molecules and tert-butoxyl radical was analyzed.
Nunes
Paulo M
PM
Centro de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal.
Estácio
Sílvia G
SG
Lopes
Gustavo T
GT
Agapito
Filipe
F
Santos
Rui C
RC
Costa Cabral
Benedito J
BJ
Borges dos Santos
Rui M
RM
Martinho Simões
José A
JA
D000475:Alkenes / Q000737:chemistry; D002244:Carbon / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D009636:Norbornanes / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D013816:Thermodynamics
D000475:Alkenes; D005609:Free Radicals; D009636:Norbornanes; D010087:Oxides; C052893:tert-butoxy; D002244:Carbon; D010100:Oxygen; C048294:2,5-norbornadiene