Ab initio and DFT study on the electrophilic addition of bromine to endo-tricyclo[3.2.1.02,4]oct-6-ene

Full geometric optimization of endo-tricyclo[3.2.1.0^2,4]oct-6-ene (endo-TCO) by ab initio and DFT methods allowed us to investigate the structure of the molecule. The double bond is endo-pyramidalized and its two faces are no longer found to be equivalent. The exo face of the double bond has regions with far more electron density (q_i,HOMO) and more negative electrostatic potential. The endo-TCO-Br₂ system was investigated at the B3LYP/6-311+G** level and the endo-TCO···Br₂(exo) molecular complex was found to be relatively more stable than the endo-TCO···Br₂(endo) complex. The cationic intermediates of the reaction were studied by ab initio and DFT methods. The bridged exo-bromonium cation(I) is relatively more stable than the endo-bromonium cation(II). An absolute exo-facial selectivity should be observed in the addition reaction of Br₂ to endo-TCO, which is caused by steric and electronic factors. The nonclassical rearranged cation IV was found to be 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 is also discussed.     

<Emphasis Type="Italic">Ab initio</Emphasis> and DFT investigation of electrophilic addition reaction of bromine to <Emphasis Type="Italic">endo,endo</Emphasis>-tetracyclo[4.2.1.1<Superscript>3,6</Superscript>.0<Superscript>2,7</Superscript>]dodeca-4,9-diene

Full geometric optimization of endo,endo-tetracyclo[4.2.1.1^3,6.0^2,7]dodeca-4,9-diene (TTDD) has been carried out by ab initio and DFT/B3LYP methods and the structure of the molecule investigated. The double bonds of TTDD molecule are endo pyramidalized. The structure of π-orbitals and their mutual interactions for TTDD molecule were investigated. The cationic intermediates and products obtained as a result of the addition reaction have been studied using the HF/6-311G(d), HF/6-311G(d,p) and B3LYP/6-311G(d) methods. The bridged bromonium cation isomerized into the more stable N- and U-type cations and the difference between the stability of these cations is small. The N- and U-type reaction products are obtained as a result of the reaction, which takes place via the cations in question. The stability of exo, exo and exo, endo isomers of N-type product are nearly the same and the formation of both isomers is feasible. The U-type product basically formed from the exo, exo-isomer. Although the U-type cation was 0.68 kcal mol⁻¹ more stable than the N-type cation, the U-type product was 4.79 kcal mol⁻¹ less stable than the N-type product. Figure The energy diagram of TTDD–Br₂ system (kcal mol⁻¹)(MP2/6-311G*//HF/6-311G*)     

Density functional theory investigation of electrophilic addition reaction of bromine to tricyclo[4.2.2.22,5]dodeca-1,5-diene1

The geometry and the electronic structure of tricyclo[4.2.2.2^2,5]dodeca-1,5-diene (TCDD) molecule were investigated by DFT/B3LYP and /B3PW91 methods using the 6-311G(d,p) and 6-311++G(d,p) basis sets. The double bonds of TCDD molecule are syn-pyramidalized. The structure of π-orbitals and their mutual interactions for TCDD molecule were investigated. Potential energy surface (PES) of the TCDD-Br₂ system was studied by B3LYP/6-311++G(d,p) method and the configurations [molecular charge-transfer (CT) complex, transition states (TS1 and TS2), intermediate (INT) and product (P)] corresponding to the stationary points (minima or saddle points) were determined. Initially, a molecular CT-complex forms between Br₂ and TCDD. With a barrier of 22.336 kcal mol^-1 the CT-complex can be activated to an intermediate (INT) with energy 15.154 kcal mol^-1 higher than that of the CT-complex. The intermediate (INT) then transforms easily (barrier 5.442 kcal mol^-1) into the final, N-type product. The total bromination is slightly exothermic. Accompanying the breaking of Br-Br bond, C1-Br, C5-Br and C2-C6 bonds are formed, and C1 = C2 and C5 = C6 double bonds transform into single bonds. The direction of the reaction is determined by the direction of intramolecular skeletal rearrangement that is realized by the formation of C2-C6 bond.

DFT and MP2 study on the electrophilic addition reaction of bromine to exo-tricyclo[3.2.1.02.4]oct-6-ene

The geometry and electronic structure of exo-tricyclo[3.2.1.0^2,4]oct-6-ene (exo-TCO) was investigated using DFT methods. The two faces of the endo-pyramidalised double bond of the molecule are not equivalent. The exo face of the double bond has regions with high electron density (q _i,HOMO) and greater negative potential. Molecular complexes of exo-TCO with bromine were investigated using the B3LYP/6-311++G(d,p) method; the exo-TCO . . . Br₂(exo) molecular complex was found to be relatively more stable than the exo-TCO . . . Br₂(endo) complex. The cationic intermediates of the reaction were studied by DFT and MP2 methods. The solvent effect was evaluated using the self-consistent isodensity polarised continuum model (SCI-PCM). The exo-bromonium cation was found to be more stable than the endo-bromonium cation. Exo-facial selectivity due to electronic and steric factors was observed upon addition of bromine to exo-TCO. The multicentre nonclassical delocalised bromocarbonium cation IV and the exo-bridged-bromonium cation I are more stable than the rearrangement cation V. The reaction products are formed via exo-bridged-bromonium I and nonclassical IV cations, which are the most stable intermediates and whose stabilities barely differ. The mechanism of the addition reaction is also discussed.     

Preparation, properties and crystal structure of two isomers of R,R,S,S- and R,S,R,S-[chloro(1,3,10,12,16,19-hexaazatetracyclo[17,3,1,1,0]tetracosane)copper(II)]

Two isomers (R,S,R,S- and R,R,S,S-) of five coordinate complex [Cu(L)Cl]⁺ have been separated and characterised. These two isomers have significantly different spectrochemical and electrochemical properties. Absorption maximum of R,S,R,S-[Cu(L)Cl]⁺ shifts to longer wavelength and its reduction potential shifts to more positive direction comparing those of R,R,S,S-[Cu(L)Cl]⁺. R,S,R,S-[Cu(L)Cl]⁺ is significantly distorted to trigonal-bipyramidal structure, whereas R,R,S,S-[Cu(L)Cl]⁺ retains almost square-planar geometry. The average bond distance of Cu-N in basal plane of R,S,R,S-[Cu(L)Cl]⁺ is longer by 0.024 Å than that of R,R,S,S-[Cu(L)Cl]⁺, whereas the bond distance of Cu-Cl in former is shorter by 0.200 Å than that in latter. The isolated square-planar complexes of R,R,S,S- and R,S,R,S-[Cu(L)](ClO₄)₂ are converted to the R,R,S,S- and R,S,R,S-[Cu(L)Cl]⁺ by the addition of Cl⁻ in nitromethane solution with the rate constants, k=1.70 (±0.02) and 8.31 (±0.07) M⁻¹ s⁻¹, respectively.