Person: ALTUN, ZİKRİ
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ALTUN
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ZİKRİ
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Publication Metadata only Two small thermodynamically stable organic dications(ELSEVIER, 2010) YUMAK YAHŞİ, AYŞE; Yumak, Ayse; Yavuz, Ilhan; Altun, Zikri; Trindle, CarlSmall multiply charged species may be long-lived without the benefit of stabilization by a medium, primarily owing to the Coulomb barrier that impedes both formation and dissociation of the systems. We extend the category of small organic dicationic structures that may possess thermodynamic stability to include derivatives of cyanoacetylene. The linear dication HCCCNH(2+) and its isomer HCCNCH(+2) are characterized in detail; according to CCSD(T)/6-31G(d,p)//MCSCF(7,13)/6-31G(d,p) estimates, HCCCNH(2+) is thermodynamically stable by 2.8 eV and the barrier to colinear dissociation is ca 4.1 eV. The isomer HCCNCH(2+) is thermodynamically stable by about 2.1 eV and the barrier to colinear dissociation is ca 4.5 eV. Preparation of these systems by charge stripping of the predecessor H2C3N monocation may be feasible. (C) 2009 Elsevier B.V. All rights reserved.Publication Metadata only Structure and energetics of cyclopropane carboxaldehyde(WILEY, 2013) BLEDA, ERDİ ATA; Trindle, Carl; Bleda, Erdi A.; Altun, ZikriWe use the energies obtained by a focal point analysis including extrapolation from results with basis sets cc-pVnZ and aug-cc-pVnZ with n up to 4 and correlation corrections through CCSD(T), to estimate thermodynamic functions for the syn and anti isomers of cyclopropane carboxaldehyde (CPCA). These agree with values obtained by well-established thermochemical schemes CBS-QB3 and G4. The structures obtained in these studies also conform to the best experimental determination of the rotational constants in the gas phase. The kinetics of gas phase interconversion of the syn- and anti-isomers of CPCA have been studied by a chirped-pulse dynamic rotational spectroscopy. Computational modeling of the internal rotational potential allows the estimate of the interconversion rates by statistical (RRKM) methods. RRKM rates using a range of barrier heights including a CBS-Q estimate are more than 10x the rates deduced from the dynamical rotational spectra. This suggests that nonstatistical effects may be limiting the rate. Detailed study of the interconversion potential by a variant of the focal point analysis suggests that previous estimates of the barrier may be too low, and thus, the inferred rice-ramsperger-kassel-marcus (RRKM) rate could be too high. These results cast some doubt on the presence of nonstatistical effects and suggest that molecular dynamics studies should be conducted to characterize the energy flow in detail. (c) 2013 Wiley Periodicals, Inc.Publication Metadata only A case study of antiaromaticity: carbomethoxy cyclopropenyl anion(SCIENTIFIC TECHNICAL RESEARCH COUNCIL TURKEY-TUBITAK, 2019) BLEDA, ERDİ ATA; Altun, Zikri; Bleda, Erdi Ata; Trindle, CarlThe simplest ideas of antiaromaticity refer to regular monocyclic systems and the eigenfunctions of the Huckel Hamiltonian for 4n pi electrons in such systems. The antiaromaticity is expressed in the energy penalty for such idealized systems relative to the Huckel energy for 2n noninteracting pi pairs. Observed systems seldom achieve the regular planar geometry assumed in this picture, owing to their ability to ease the antiaromaticity penalty by departures from the regular geometry and also by export of the 4n pi electrons' charge to substituents. In this report we estimate numerical values for the stabilization derived from such departures from the structure and the charge distribution of the idealized antiaromatic cyclopropenyl anion for a specific case, 3-dehydro-3-methyl carboxylate cyclopropenyl anion 1(-) using the thermochemical scheme CBSQB3 supplemented by CCSD(T) calculations. According to the isodesmic reaction, the anion 1(-) is destabilized by about 10-15 kcal/mol relative to the saturated 3-dehydro-3-methylcarboxylate cyclopropyl anion 2(-). We propose that the anion relieves a portion of the antiaromatic destabilization by (a) pyramidalization of one carbon of the ring, and (b) export of negative charge into the ester substituent. Both of these responses are expressed in the equilibrium structure of the anion. In the course of the study we estimate the acidity of several related anions and the enthalpy of formation of their neutral conjugate acids, and describe the interconversion of 1 to the dehydrotriafulvalene anion 3(-) by reaction with CO2. [GRAPHICS] .