Ph.D. Theses
Permanent URI for this collection
Browse
Browsing Ph.D. Theses by Subject "Conformational analysis."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item A theoretical investigation of solvent effect on the conformational equilibria of 2-substituted cyclohexanone ketal derivatives(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1995., 1995.) Sağ-Erdem, Safiye.; Varnalı, Tereza.; Aviyente, Viktorya.The conformational equilibria of 6-substituted-1,4-dioxospiro-[4.5]decanes and 7substituted-1,5-dioxospiro [5.5]undecanes, relatively complex polar systems, with substituents X=-CH3, -F, -CI, -CN, -OH, -OCH3, -N02 have been studied. The complete geometry optimizations have been carried out sequentially in the gas phase and in solution to represent the effect of the solvent. The methodology consists of the semiempirical PM3 hamiltonian and the self consistent reaction field computations. The effect of the solvent is implemented by the "cavity model". Ab initio calculations have also been performed on 1 ,1 , 2-trihydroxy ethane as a model for the hydroxy derivatives of the ketals studied.The discussion of the results is focused on the solvent effects arising from structural aspects, steric and electrostatic interactions on the axial/equatorial relative stability. The role played by multipole moments is considered. Good agreement with available experimental data and with previous theoretical studies has been obtained in general. The semiempirical methods and the simple solvent models are useful to predict the main role of solute-solvent interactions in conformational equilibria of complex systems for which ab initio calculations cannot be performed.Item Conformational analysis of 2-substituted cyclohexanone ketal derivatives by molecular mechanics and nuclear magnetic resonance(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1986., 1986.) Varnalı, Tereza.; Özbal, Hadi.The present study is concerned with the application of the Molecular Mechanics Method to 2-substituted cyclohexanoneketals. The object is to find the conformational free energy difference between the equilibrating conformers and to compare the theoretical results to those found experimentally. For the application of molecular mechanics, models of the compounds underinvestigation were described, the inter-atomic distances and angles were computed, the most important interactions were determined and the parameters needed for calculations of the interactions and functions relating parameter to energy were chosen. First, molecular mechanics was applied to spiro- [5,4]-1-halo-6,9-dioxodecane (1 in Fig. 1.1.1) and spiro-[5,5]-1-halo-6, 10-dioxoundecane(2 in Fig.1.1.1) where the halogen was chlorine or bromine. The results obtained theoretically showed preference for the conformer bearing the axialhalogen in (2) system and the conformer bearing the equational halogenin (1) system, being in accordance to experimental results reported by Zefirovet et. al. Secondly, molecular mechanics was applied to spiro- [5,4]-1-halo-6,9-dioxodecane and spiro-[5,5]-1-nitro-6,10 undecane and the results obtained theoretically in contrast to halogens, showed preference for the conformation in which the nitro group is equatorial in both cases ( 1 ) and ( 2 ). Finally, the 4-t-butyl derivatives of the nitro-(1) and (2) systems, and the (1) and (2) systems were synthesized and the free energy difference between the equilibrating conformers were obtained experimentally using NMR parameters. Experimental results were in parallel to those found theoretically. In previous studies the nitro group has been shown to behave differently than halogens and similar groups due to its electronic distribution, size, structure and formal change. The unique behavior of the nitro group has been shown once more both theoretically and experimentally.