A quantum-chemical study on the electrophilic addition of bromine to homobenzonorbomadiene

1029-1032SCF-MO-LCAO AM1 calculations have been performed for 1:1 molecular system of bromine with homobenzonorbornadiene (HBNB) and their stable configurations have been determined. The stable configurations of the HBNB-Br2 system correspond to HBNB-Br2 (exo) and HBNB-Br2 (endo) molecular complexes which are formed by the exo and endo orientations of Br2 molecule to the double bond of HBNB in axial position, respectively. Exo-molecular complex has been found to be relatively more stable than the endo-complex. The cationic intermediates of the reaction have been studied by ab initio SCF method in STO-3G and STO-3G* basis and also by MNDO semiempirical route. Exo-bromonium cation is found to be more stable than endo-bromonium cation according to both the methods. The nonclassical delocalized bromocarbonium cation is the most stable among these cations according to both methods, and the ionic addition reactions occur via this cation

Quantum-chemical investigation of electrophilic addition of bromine to norbornadiene

1773-1776In the electrophilic addition of bromine to norbornadiene, the intermediate molecular complexes between norbornadiene and bromine have been investigated and their stable configurations determined using AM1 semiempirical method. The geometric parameters and stabilization energies of the complexes have been calculated. The exo and endo adducts are found to be nearly isoenergetic, but an exo selectivity has been observed. The cationic intermediates of the reaction have been studied by ab initio SCF method in STO-3G and STO-3G* basis and al so by MNDO semiempirical route. Exo-bromonium cation is found to be more stable than endo-bromonium cation according to both the methods. The results obtained indicate that a multicenter non-classical bromocarbonium cation formed by the rearrangement of exo bromonium cation is the most stable one among the cationic intermediates. It is likely that the ionic addition reaction proceeds via the non-classical bromocarbonium ion and results in the formation of the rearranged products

Quantum chemical investigation of molecular complexes formed with bromine molecule of bicyclo[3.3.1]nonylidenebicyclo[3.3.1]nonane and its derivatives

1557-1563The strain energies and the pyramidalization parameters of bicycle [3.3.l]nonylydenebicyclo[3.3. l]nonane(BBN), trans(1-methyl-2-bicyclo[3.3 .1]-l-methyl bicyclo [3.3.1]nonane (DMBBN) and trans-(1-tert-butyl-2-bicyclo[3.3.1])-1–tertbutylbicyclo [3.3.1] nonane (DBBBN) molecules have been calculated using MM2 and AMBER molecular mechanic methods. The strain energy and the pyramidalization degree of the molecule are increased by increasing the volume of R groups at the allylic position of the double bond. The electronic structure of the molecules have been investigated by semiempirical PM3 method. The results of molecular mechanic and PM3 methods, agree with the X-ray results and shows that the double bond of BBN molecule has a planar structure. The 1: 1 π-molecular complexes of the molecules formed with Br2 are investigated using PM3 method and it is seen that their stable configuration has an axial structure. The electronic and the steric factors affecting the structure and the stability of the molecular complexes have been studied. It is found that the DMBBN ... Br2 complex is more stable than the BBN ... Br2 complex. It is determined that DBBBN ... Br2 complex containing the bulky tert-butyl group has the lowest stabilization energy among the investigated molecular complexes

A quantum chemical investigation of electrophilic addition reaction of bromine to bicyclo[3.2.2]nona-6,8-diene

221-226Full geometric optimization of bicyclo[3.2.2]nona-6,8-diene (BND) has been done by semiempirical and ab initio methods and the structure of the molecule has also been investigated. The double bond (I) situated in the opposite direction of methylene group in END molecule is more exo pyramidalized than the other double bond (II). The electron density (qi,HOMO) of the double bond(I) in HOMO of the molecule is more than that of the (II) double bond. Exo and endo faces of exo pyramidalized double bonds of the molecule are not equal and electron density is higher in endo faces. The molecular complexes of BND with bromine have been investigated by AM1 method and their stable configurations determined. The reason for endo molecular complexes being more stable than exo is that the stability is caused by electronic and steric factors. Because of electronic factors, BND ... Br2(endo1) complex is more stable than BND Br2 ...(endo2). The endo-bridged bromonium cation(I) is relatively more stable than the endo-bridged cation(IV). Endo- facial stereoselectivity and regioselectivity should be observed in the addition of bromine to BND molecule. Endo-facial stereoselectivity is caused by electronic and steric effects, regioselectivity by electronic effects. The rearranged bromocarbonium cation(V) is the most stable among the cationic intermediates and the ionic addition reaction occurs via this cation