An extensive study of disubstituted cycloalkanes like CnH2n where n=3,4,5 and 6 using DFT((U)B3LYP/6-31G(d) and 6-311+G(2df,2p)) calculations is presented focusing on the effect of pyramidalization of the radical center. A potential energy surface (PES) analysis shows that the radical prefers to pyramidalize anti to the two cis fluorines in the disubstituted cycloalkanes. The degree of pyramidalization for 1,2-difluorocyclopropyl radical is 43.9o away from the cis fluorines whereas for 1,3-difluorocyclobutyl radical, 1,3-difluorocyclopentyl radical and 1,3-difluorocyclohexyl radical is 3.8o, 5.4o and 14.5o respectively away from the cis fluorines. The importance of this pyramidality effect in these compounds is discussed in context with the carbon-hydrogen bond dissociation energies (BDE's) because the preference of the radical centers to pyramidalize anti to the fluorines affects the bond dissociation energy. Importance of steric effect and unfavorable electronic interactions have been extensively explored in planar permethylated cyclobutadiene (Me4CBD) and cyclooctatetraene (Me8COT) using ((U)B3LYP/6-31G(d) and 6-311+G(2df,2p)) calculations. It is thought that steric interactions dominate electronic interactions in Me8COT, while this works opposite in case of Me4CBT. Instead, in Me4CBD the number of unfavorable electronic interactions between π bonds and out-of-plane hydrogens plays the dominant role in determining the relative energies. Interactions between the π bonds of CBD and the out-of-plane hydrogens on carbons attached to the four-membered ring becomes very interesting when the ring size changes. With ethano bridge on the cyclobutadiene ring interaction with the diagonal bonds results in non-bonding AOs across the other diagonal having the opposite phase in the highest occupied (HO)MO. If the HOMO and LUMO are switched, bis-ethano-bridged tetrahedrane is formed. It is suggested that bis-ethano-bridged tetrahedrane is thermodynamically more stable than bis-ethano-bridged cyclobutadienes. While the reverse is true for unsubstituted cyclobutadienes. The ability of ethano bridges to reverse the usual order is because it causes the doubly-bonded carbons to pyramidalize.

The synthesis of cyclic allenes with eight or less skeletal C-atoms, known as highly strained organic compounds, has for the past decades attracted increasing interest. The first part of study describes an investigation aimed at the incorporation of an allene unit into a natural compound, being &amp / #945 / -pinene, by using &amp / #946 / -elimination method. The two double-bond isomers 310 and 299b were synthesized as key compounds. Treatment of 310 with t-BuOK resulted in the formation of ketone 308 and diene 313. For the formation of 308, the cyclic allene 300 was proposed as an intermediate. Treatment of 299b, with t-BuOK gave arise to the diene 313 and the dimerization product 322. On the basis of density-functional-theory (DFT) calculations on the allene 300 and the alkyne 320, the formation of the latter as the intermediate was excluded. In the second part of study, the stability of endo-carbene 304 was investigated. Previous studies indicated, during the formation of intermediate 264, no exo-carbene 330 structure could be optimized in its free carbene form. At this point, we were curious about the stability of endo-cyclopropylidene 304 not discussed before in literature. First, addition of bromofluorocarbene to anti-7-ethylbenzonorbornadiene (352) was aimed to isolate the endo-adduct 302b. However, no carbene addition reaction was observed caused by pyramidalization on double bond respect to the methoxy derivative, 363b. Therefore, the bromine was introduced to C-7 carbon atom. Treatment of 302a with MeLi in the presence of furan, gave furan adduct 306a confirmed the formation of allene 305a as a reactive intermediate. Theoretical calculations showed endo-carbene 304a was optimized in the free carbene form . However, it readily isomerizes to allene 305a afforded furan adduct 306a.

ABSTRACT FUNCTIONALIZATION OF SATURATED BICYCLIC HYDROCARBONS: HIGH TEMPERATURE BROMINATION &Ouml / zer, Melek Sermin M.Sc., Department of Chemistry Supervisor: Prof. Dr. Metin Balci January 2011, 139 pages Although hydrocarbons are readily available and extremely cheap starting materials, they cannot be used in synthetic chemistry without prior activation. The selective functionalization of saturated hydrocarbons under mild conditions is of both biochemical and industrial importance. Initially, saturated hydrocarbons such as octahydro-1H-indene 80, octahydro-1H-4,7-methanoindene 81 and bicyclo[4.2.0]octan-7-one 82 were synthesized as starting materials. Then high temperature bromination reactions of these saturated hydrocarbons as a method for C-H bond activation have been investigated and the synthetic application of the formed intermediates has been searched. Furthermore, the role of the alkyl substituents in tricyclic systems and the effect of carbonyl group in bicyclo[4.2.0] octan-7-one 82 have been studied and the mechanism for the formation of the products have been discussed. Finally, whole products were conscientiously purified and characterized.