Fatma Sevin

Oxidation of cyclohexane catalyzed by metal-ion-exchanged zeolites

The ion-exchange rates and capacities of the zeolite NaY for the Cu(II), Co(II), and Pb(II) metal ions were investigated. Ion-exchange equilibria were achieved in approximately 72 h for all the metal ions. The maximum ion exchange of metal ions into the zeolite was found to be 120 mg Pb(II), 110 mg Cu(II), and 100 mg Co(II) per gram of zeolite NaY. It is observed that the exchange capacity of a zeolite varies with the exchanged metal ion and the amount of metal ions exchanged into zeolite decreases in the sequence Pb(II) > Cu(II) > Co(II). Application of the metal-ion-exchanged zeolites in oxidation of cyclohexane in liquid phase with visible light was examined and it is observed that the order of reactivity of the zeolites for the conversion of cyclohexane to cyclohexanone and cyclohexanol is CuY > CoY > PbY. It is found that conversion increases by increase of the empty active sites of a zeolite and the formation of cyclohexanol is favored initially, but the cyclohexanol is subsequently converted to cyclohexanone.

Diastereoselective control through hydrogen bonding in the aziridination of the chiral allylic alcohols by acetoxyaminoquinazolinone.

A high diastereoselectivity (up to >99:1) is found for the aziridinations of chiral allylic alcohols with acetoxyaminoquinazolinone (Q-NHOAc). The selectivity is explained in terms of hydrogen bonding between the hydroxy functionality of the allylic alcohol and the remote carbonyl group of the quinazolinone.

Reaction mechanism of copper(I) catalysed head-to-head dimerization of 1-alkynes : an experimental and theoretical study

Abstract The Strauss reaction is regioselective and unique for the head-to-head coupling of terminal acetylenes. For the success of the catalytic conversion, the presence of copper(l) carboxylate is necessary. The corresponding carboxylic acid may be used pure, as solvent, or diluted in non-nucleophilic solvents. However, its presence in excess is also necessary. The formation of the product, 1,4-dialkylenynes, shows some stereoselectivity. The E isomer is always dominant in the mixture, but the E/Z ratio may be manipulated by the steric effects of the R groups of the carboxylic acid and of the monomers as well. The nucleophilic solvents such as HZO, ROH and phosphine ligands inhibit the catalytic reaction. The isolated products are the copper acetylides or its phosphine complexes, respectively. Mesitylacetylene and p -nitrophenylacetylene do not undergo the catalytic conversion. However, the former gives the cross-product with phenylacetylene. The possible mechanism of the reaction is discussed and the suggested pathway is supported with computational calculations.

Trapping of a cycloheptatetraene in the reaction of atomic carbon with phenol

Reaction of atomic carbon with phenol generates tropone in a reaction postulated to proceed via the hydroxycycloheptatetraenes, which rearrange to tropone. When the hydroxyphenylcarbenes are generated by the C atom deoxygenation of the corresponding aldehydes, the meta and para isomers produce tropone; the ortho isomer does not.

The effect of the proton on electropolymerization of the thiophene

Abstract Electropolymerization of thiophene was investigated in neutral and acidic medium from the standpoint of film formation and conductivity. Results obtained from voltammetric investigations have shown that proton affects both the electropolymerization of thiophene and its conductivity. This effect was explained by theoretical calculations using molecular mechanic (MM+, MM2) and semi-empirical (AM1) methods. From these calculations, it is seen that proton is significantly important in the stabilization and growth of the polymer. Proton is added to the sulfur atom in the polymer, which has a basic character because of its lone-pair electrons. With the addition of proton, the effect of the lone-pair electrons to the delocalization existing in the ring and the contribution to the conductivity of polythiophene is removed. Thus, the conjugation in the ring is reduced to the π-system in carbon skeleton and the structure of the protonated polythiophene resembles to that of polyacetylene.

DFT study of the 1-octene metathesis reaction mechanism with WCl6/C catalytic system.

A catalytic system consisting of tungsten carbene generated from WCl(6) and an atomic carbon is investigated theoretically for the metathesis of 1-octene at B3LYP/extended LANL2DZ level of DFT. The ground-state geometries and charge distributions of the structures belonging to the reaction mechanism are located. Energetics for the complete set of reactions, involving the formation of the tungsten carbene precatalyst, Cl(4)WCCl(2), the formation of tungsten methylidene and tungsten heptylidene with this precatalyst, and finally productive and degenerative metathesis steps with these alkylidene species are calculated in terms of total electronic energy and thermal energies. The free-energy (ΔG(298)) surfaces of the structures involved in the related reactions are constructed. In addition, solvent effects on the single point energies of the structures are investigated for two different solvents, namely, cyclohexane and chloroform. The results indicate that the formation of the catalytically active heptylidene is energetically favored in comparison to the formation of methylidene, while the degenerative and productive metathesis steps are competitive. In the catalytic cycle, the formation of ethylene is exothermic, while the formation of 7-tetradecene is endothermic. As expected, solvent effects on the metathesis reactions are minor and solvation does not cause any change in the directions of the overall metathesis reactions.

Intramolecular Trapping of Strained Bicyclic Allene in Carbon Atom Reactions

We report here the intermolecular trapping of endo-bicyclo[3.2.1]octa-2,3-dien-6-ol generated by reacting C with endo-bicyclo[2.2.1]hept-5-en-2-ol. The fragmentation reaction through endo-bicyclo[3.2.1]octa-2,3-dien-6-ol favours product (5Z)-octa-1,5dien-7-yn-3-ol rather than the intramolecular trapping product 2-oxatricyclo [4.2.1.03,8] non-4-ene. We also describe this reaction theoretically by means of the AM1 semiempirical method.

Reactions of Atomic Carbon with 2-Norbornene

Reaction of atomic carbon with 2-norbornene,1 generates octa-3,7-dien-1-yne, 5 in a reaction over bicyclo[3.2.1]octa-2,3-diene, 4 which fragments to 5. 4 has also been trapped by THF. The potential energy surfaces of C8H10 have been evaluated by means of the AMI semiempirical method.