A quantum-chemical investigation on electrophilic addition of chlorine to benzonorbornadiene

884-887The chlorine-benzonorbornadiene molecular complexes have been investigated by AM1 semiempirical method and their stable configurations have been determined. The geometric parameters and stabilisation energies of the complexes have been calculated. Exo-molecular complex has been found to be relatively more stable than the endo-complex. The various cationic and radicalic intermediates of the electrophilic addition of chlorine to &nbsp;benzonorbornadiene have been studied using MNDO and ab initio methods. It has been found that the exo-chloronium cation is 7.9 kJ/mol and 30.6 kJ/mol relatively more stable than the endo-chloronium ion according to MNDO and STO-3G methods, respectively. The non-classical delocalized chloronium cation has been found to be the most stable one among the cationic intermediates formed in the reaction, and so the ionic addition reaction proceeds via this cation. According to the methods used in the study, the exo-chloro radical is relatively more stable than the endo-chloro radical. Radicalic addition is predicted to occur via these intermediate radicals. </span

An analysis of the conformation and electronic structure of newly synthesized cryptand

1013-1015Using molecular mechanical methods (MM2, AMBER, OPLS), a conformational analysis of a newly synthesized cryptand is made and its stable conformations are determined. The electronic structures of the stable conformations are analysed by the AM1 method, and its donor-acceptor characteristics are investigated

A DFT investigation of Diels-Alder reaction of ethyl propiolate to the cage-annulated hexacyclo[7.5.2.01,6.06,13.08,12.010,14]hexadeca-2,4-diene-7,16-dione

The Diels–Alder (DA) reaction between the cage-annulated diene hexacyclo[7.5.2.01,6.06,13.08,12.010,14]hexadeca-2,4-diene-7,16-dione (HHDD) with a cyclohexa-1,3-diene moiety and ethyl propiolate (EP) dienophile was investigated by the DFT method at the B3LYP/6-31+G(d,p) level to elucidate the mechanism and regioselectivity features of the reaction. The geometrical and electronic structures of the caged diene HHDD and EP were studied at B3LYP/6-31+G(d,p) level. In order to identify facial- and regio-selectivity of the DA reaction of HHDD and EP, the frontier molecular orbital (FMO) interactions of the reactants according to the FMO theory, and the molecular electrostatic potential map of HHDD were examined. The potential energy surface (PES) of the related DA reaction was calculated, and optimizations of transition states and of products corresponding to critical points on the PES were performed at the B3LYP/6-31+G(d,p), and their configurations were determined. In addition, the thermodynamic and kinetic parameters of each possible cycloaddition reaction were calculated using the B3LYP/6-31+G(d,p) method to determine whether the reaction occurs under thermodynamic or kinetic control. The thermochemical results showed that the related DA cycloaddition proceeds under kinetic control, and the activation energies of syn cycloadditions are clearly lower than that of anti cycloadditions. The theoretical calculations are in good agreement with experimental results

A quantum chemical investigation of electrophilic addition reaction of bromine to <i>exo-</i>tricyclo[3.2.1.0^2.4]oct-6-ene

2497-2502Full geometric optimization of exo-tricyclo[3.2.1.02.4]oct-6-ene (exoTCO) has been done by the semiempirical methods and the structure of the molecule investigated. The double bond of molecule is endo-pyramidalized and the two faces of double bond are no longer equivalent. Exo face of the double bond of the molecule has regions having high electron density (qi,HOMO) and bigger negative potential. The exoTCO ... Br2 system has been investigated by AM1 method and exoTCO ... Br2(exo) molecular complex has been found to be relatively more stable than the exo ... Br2(endo) complex. The cationic intermediates of the reaction have been studied by semiempirical methods. Exo-bromonium cation is found to be more stable than endo bromonium cation. Exo-facial selectivity has been observed in the addition reaction to exoTCO of bromine which is caused by electronic and steric effects. Exo-classical bromocarbonium cation(III) is more stable than rearrangament cation(V) which is formed with Wagner-Meerwein rearrangament. Bromocarbonium cation(III) is the most stable ion among the cationic intermediates and the ionic addition occurs via the formation of this cation. The mechanism of the addition reaction has also been discussed

A quantum-chemical study on the electrophilic addition of chlorine and bromine to bicyclo [2. 2. 2] octa-2,5-diene

303-306The molecular complexes of bicyclo [2. 2. 2] octa-2,5-diene with chlorine and bromine have been investigated using AM1 semiempirical method. The geometric parameters and stabilisation energies related to the complexes have been calculated. The exo and endo adducts are found to be nearly isoenergetic. The greater stearic repulsions in the exo complex are apparently compensated by increased electronic stabilisation. The cationic intermediates of the electrophilic addition of chlorine and bromine to bicyclo [2. 2. 2] octa-2,5-diene have been investigated by MNDO and ab initio methods. The results obtained reveal that the bridged endo-halogenium cation is relatively more stable than the bridged exo-halogenium cation for both chlorine and bromine. The rearranged cations have been found to be the most stable ones among the cationic intermediates formed in the reaction. It is plausible that the ionic addition reactions proceed via the most stable cations. Essentially, the rearranged addition products are predicted to form in the ionic addition reactions of ch lorine and bromine to bicyclo [2. 2. 2] octa-2,5-diene. </span

The theoretical conformation analyses of polyoxanorbornene chain

2491-2496The conformational analysis of polyoxanorbornene (PONB) chain is <span style="mso-bidi-font-family: Arial;mso-bidi-language:HI">investigated <span style="mso-bidi-language: HI">with the AM1<span style="mso-bidi-font-family:Arial;mso-bidi-language: HI">, MM2, AMBER and OPLS methods taking into consideration the possibility of binding of oxanorbornene monomers to each other at various positions. i.e. exo-exo, exo-endo, endo-endo. The chain that is formed by connecting exo-endo positions of the monomers has lower torsional barrier energy than those formed with <span style="mso-bidi-font-family: Arial;mso-bidi-language:HI">bonds at other positions and has more flexibility. It is determined that thredisyndiotactic chain formed <span style="mso-bidi-font-family:Arial;mso-bidi-language: HI">by exo-endo addition has coil shape. Disyndiotactic chain formed by connecting oxanorbornene monomers in mixed type has a linear structure. It is found that the repeat unit conformations of thredisyndiotatic and disyndiotactic chains of PONB are TGTG and (TGTG)2, respectively. </span

The quantum chemical investigation of the addition reactions of Br₂ to homocubylidenehomocubane and its derivatives

2179-2185The electronic and geometric structures of homocubylidenehomocubane (HC), trans- (l - methyl-2-homocubyliden)- 1- methylhomocubane (DMHC) and trans -(1-tert -butyl-2-homocubyliden)- 1-tert-butylhomocubane (DBHC) molecules have been investigated by B3LY P/6-311 G* method. These results agree with X-ray results and show that the double bond of HC moleecule has a planar structure, while the double bonds in DMHC and DBHC molecule are almost planar. The complexes (1:1 π complexes) of the molecules with Br2 have been investigated by B3LY P/6-311 G *method and it is observed that the stable configurations have an axial structure. The electronic and the steric factors affecting the structure and the stability of the molecular complexes have been studied, it is observed that the DMHC ... Br2 complex is more stable than HC ... Br2 complex. The DBHC ... Br2 complex containing the bulky tert -butyl group has stability of sterically encumbered olefin-brom complex and it depends on the nature of 'cage' substituents on the double bond carbons. The bridged bromonium cation is the more stable cation among the cationic intermediates formed in the addition reaction of bromine to HC and the reaction occurs via this cation. The nucleophilic attack by bromide ion is not sterically prevented to HC-Br+ bridged bromonium cation and as a result, normal 9, 9'-dibromide product is formed. The nucleophilic attack by bromide ion is sterically prevented to AD-Br+ bridged bromonium cation

A quantum-chemical study on bi(1,2,3-triazole) molecule

413-417The conformational analysis of 4,4'-bi(1H-I ,2,3-triazole)A, 5,5'-bi (1<i style="mso-bidi-font-style: normal">H-1,2,3-triazole) B and 5,5'-bi (2H-1,2,3 -triazole) C tautomers of flexible bi(1,2,3-triazole) molecule containing various reaction centres has been performed by semiempirical methods AM1 and PM3. Furthermore, electronic properties of the tautomers and the effect of conformational changing on their electronic properties have also been investigated. In order to determine the orientation sites of proton attacks at the bitriazole system, molecular electrostatic potentials of the tautomers have been calculated. Conformations and electronic properties of the monoprotonated species of the tautomers have also been studied. Proton affinity of the tautomers has been calculated for different nitrogens, and possible protonation centres determined. Moreover, the complex formation ability of the tautomers with metal cations has been evaluated and discussed.</span

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