A new insight on the gas phase retro-diels - alder reaction of bicyclic compounds: density functional theory calculations
- Authors
- Mora, Jos? Ram?n
- Format
- Article
- Status
- publishedVersion
- Description
The mechanisms of the gas-phase thermal decomposition of bicyclo[2.2.1]heptadiene and 3,7,7-trimethylbicyclo[2.2.1]hept-2-ene were examined by density functional theory calculations with the hybrid functionals: B3LYP, CAM-B3LYP, MPW1PW91, and PBEPBE. Reasonable agreements were found between theoretical and experimental values with the B3LYP hybrid functional. Three molecular concerted pathways for bicyclo[2.2.1]heptadiene decomposition are proposed. The retro-Diels?Alder (retro-DA) pathway yields cyclopentadiene and acetylene through a nearly synchronous transition state structure (Sy = 0.97). The other two reaction channels are stepwise with a common step with the formation of the intermediate bicyclo[4.1.0] heptadiene. This reaction is dominated by C?C bond breaking leading to the methylene migration by an early transition state in the reaction coordinate (Sy = 0.91). The rearrangements of the latter intermediate producing toluene were also studied. The retro-DA elimination of 3,7,7-trimethylbicyclo[2.2.1]hept-2-ene gives 1,5,5-trimethyl-cyclopenta-1,3-diene in a less synchronous process (Sy = 0.77). This fact may be due to the electronic effects of the methyl substituent. The latter product is unstable and undergoes methyl migrations to give a more stable isomer 1,2,3-trimethylcyclopenta-1,3-diene. The stepwise mechanism for the retro-DA reaction through a biradical intermediate appears to be unfavourable because the barrier is bigger than that for the concerted reaction.
Universidad Agraria del Ecuador
http://www.scopus.com/record/display.uri?eid=2-s2.0-84958179462&origin=resultslist&sort=plf-f&src=s&st1=
- Publication Year
- 2015
- Language
- eng
- Topic
- BICYCLO
HEPTADIENE
GAS-PHASE ELIMINATION
THEORETICAL CALCULTIONS
- Repository
- Repositorio SENESCYT
- Rights
- openAccess
- License
- restrictedAccess