DETERMINATION OF CERTAIN THERMODYNAMIC AND GEOMETRIC VALUES AND CONDENSATION MECHANISM OF ß-HIMACHALENE AND DIBROMOCARBENE USING DENSITY FUNCTIONAL THEORY (DFT)

 

M. El Idrissi1, A. Zeroual1, A. Benharref2, A. El Hajbi1*

1Laboratoire de Chimie Physique, Département de Chimie, Faculté des Sciences, Université Chouaïb Doukkali,

 BP 20, 24000 El Jadida, Morocco.

2 Laboratoire de Chimie Biomoléculaire, Substances Naturelles et Réactivité, URAC 16, Faculté des Sciences Semlalia,

Université Cadi Ayyad, BP 2390, 40000 Marrakech, Morocco.

* Corresponding author. Email: a_elhajbi@yahoo.fr

Received: 11 January 2013; revised version accepted: 27 April 2013

 

Abstract

     Equimolar condensation of ß-himachalene and dibromocarbene results in a single product (1S,3R,8R)-2,2-dibromo-3,7,7,10-tetramethyl-tricyclo[6,4,0,01,3]dodec-9-ene. When ß-himachalene reacts with an excess of dibromocarbene under the same conditions the result is two tetrabromate products (1S,3R,8R,9S,11R)-2,2,10,10-tetrabromo-3,7,7,11-tetramethyltetracyclo[6,5,0,01.2,09.116]tridecane) and (1S,3R,8R,9R,11S)-3,7,7,11- tetrabromo-3,7,7,11-tetramethyltetracyclo[6,5,0,01.2,09.11,7]tridecane. Study using density functional theory (DFT) shows that both reactions are exothermic. In the equimolar reaction, the reaction occurs at the a side of the C6=C7 double bond. This stereoselectivity is kinetically controlled. Our study shows that the regioselectivity is controlled by charge transfer. An excess of dibromocarbene leads to reaction at the C2=C3 double bond to produce two diastereoisomers, with almost equal probability of the reaction taking place at the a or ß side. Geometric parameters of the products obtained were optimized using DFT and compared to the experimental results.

 

Keywords: ß-himachalene; DFT (Density Functional Theory); Stereoselectivity; Frontier orbitals; Interatomic distances.

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