Branko S. Jursic

DFT study of the Diels–Alder reactions between ethylene with buta-1,3-diene and cyclopentadiene

A set of DFT methods (Xa, HFB, S-VWN, B–LYP; B–HandH and Becke3-LYP) has been used for the calculation of the transition states and energy barriers of the Diels–Alder reaction of ethylene with buta-1,3-diene and cyclopentadiene. The pure DFT methods overestimate the bond lengths, while the hybrid methods give values much closer to those obtained by conventional ab initio methods. The ratio of the σ-forming bonds to the π-breaking bonds is in excellent correlation to the predicted electronic energy barriers for these reactions. The local spin density approximation (S–VWN) fails completely giving a negative value for the classical energy barrier height for the addition of ethylene to buta-1,3-diene. On the other hand, the vibrational adiabatic barrier heights predicted by B-LYP/6-31G** and the hybrid Becke3-LYP/6-31G** theoretical models are in excellent agreement with available experimental data for both reactions.

Synthetic application of micellar catalysis. Williamson's synthesis of ethers

Abstract A simple, rapid and efficient procedure for the preparation of di-alkyl, simple phenyl-alkyi and hindered phenyl-alkyi ethers has been developed. Based on the principle of micellar catalysis the method involves alkylation of the alkoxide or the phenoxide ion with an alkyi chloride at 80°C in the presence of cationic micelles. For the preparation of phenyl-alkyl ethers normal micelles were used, while for the di-alkyl ethers reverse micelles were more effective. By increasing the ionic strength of the solution the rate of formation of phenyl-alkyl ethers could be increased.

AM1 Semiempirical study of reactivity of benzo[b]- and benzo[c]-thiophene as dienes in Diels–Alder reactions

We have undertaken an AM1 semiempirical study to examine the capability of benzothiophene to function as a diene in Diels–Alder reactions. Two approaches are considered: the evaluation of the aromaticity of dienes and corresponding transition-state structures, and the estimation of activation barriers. The aromaticity was determined from the heats of hydrogenation. The study was performed for the addition of ethene, tetracyanoethene and malefic anhydride to benzothiophenes. The theoretical data were in full agreement with the experimental data demonstrating the capability of these methods correctly to predict the reactivity of benzothiophenes, and the feasibility of their cycloaddition reactions.

Theoretical study of the Diels–Alder reaction between the S-methylthiophenium ion and ethene

The capability and activation of thiophene as a diene for the Diels–Alder reactions has been investigated by ab initio methods. The reactants and transition structures are optimized with RHF/3-21 + G*, RHF/6-31 + G* and MP2/6-31 + G*. Energies are evaluated with the same level of theory and by single point calculations employing MP2/6-31 + G*//RHF/6-31 + G* and MP3/6-31 + G*// MP2/6-31 + G* methods. The ab initio calculated geometries are compared with experimental data, where available. The relative reactivity of buta-1,3-diene, thiophene and the S-methylthiophenium ion were estimated by comparing their FMO energy gap with ethene as the dienophile. The predicted activation energies are in full agreement with the qualitative determination of reactivity and suggest that thiophene is not a suitable diene for the Diels–Alder reaction. For the S-methylthiophenium ion, the predicted activation energy may be reached under normal reaction conditions. Thus S-methylthiophenium should be a suitable diene for the Diels–Alder reactions.

1H NMR study of hydrogen bonding of fluorinated alcohols with ethers

Abstract The hydrogen bonding of TFE and HFIP with t-BuOCH 3 (1) and PhOCH 3 (2) was studied using 1 H nmr. The Δ δ values of carbon-bound hydrogens in 1 and 2 show good linear correlation with the alcohol acidity.

Ab initio and hybrid density functional theory studiesof the forward and reverse barriers for theC2H4 + H → C2H5 reaction

Ab initio and density functional theory (DFT) methods have been used to compute the potential energy surface of the C2H4 + H → C 2H5 reaction. It was demonstrated that the computation of the forward reaction barrier is a very difficult problem. Even high level ab initio methods, such as MP2 and QCISD, had problems coming close to the experimental value. It was demonstrated that the G2 computational method predicts a very accurate energy profile for the reaction. DFT methods have a considerable problem in finding and optimizing the transition state structure. Many of these produced negative activation barriers. It was suggested that DFT methods overestimate the total energy of the hydrogen radical. Because of this effect, the heat of the reaction and the barrier of the reaction are too low. If this problem is solved, the energies generated by hybrid DFT methods for reactions which involve the hydrogen radical should be very close to experimental values.

Selective bromination of the aromatic ring in ω-phenylpolyoxaalkanes and alkanols in micelles

Abstract The regioselectivity of bromination of ω -phenylpolyoxaalkanes and alkanols by bromine in aqueous solution of dodecyl sulfate (SDS) and aqueous solution of cetyltrimethylammonium bromide (CTAB) are shown to be related to the average orientation of substrate as indicated by 1 H NMR studies. Thus ortho-bromination is promoted at higher concentrations of the surfactant relative to pure water. In contrast, at an equal ratio of the surfactant and substrate para-bromination is promoted. The results are discussed with respect to the average orientation of substrate in a micellar microenvironment and the formation of an ether-bromine comples as possible bromination agent.

Dehydration of Aldoximes by Dichlorocarbene in Reverse Micelle

Abstract The use of reverse micelle to catalyze the dehydration, on a preparative scale, of aldoximes to nitriles by dichlorocarbene is reported.

The Selective Methylation of 4-Ethoxycarbonyl-3-Methylpyrazolin-5-One with Dimethyl Sulfate

Abstract The methylation of some pyrazolin-5-ones with dimethyl sulfate in different reaction conditions is described, ft is found that it is possible achived selective introducing of methyl group in desired position of pyrazolin-5-one ring which is of great interest for preparation of many analgesics and antipyretics with pyrazolin-5-one unit.

Neighboring sulfur participation in the solvolysis of 2-(ω-alkylthioalkyl)-3-methyl-2-cyclohexenyl p-nitrobenzoates

Abstract As shown by kinetic and product analysis, the solvolysis of 7 and 8 in 97% TFE includes several competitive reactions, one of them being neighboring sulfur participation and formation of intermediate cyclic sulfonium cation.