Conformational Analysis of Some Cyclic Structures

Russell, Marie Ann (1981) Conformational Analysis of Some Cyclic Structures. PhD thesis, University of Glasgow.

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Abstract

This thesis is composed of two parts: in the first the results from molecular mechanical calculations on cycloundecanes and cycloundecenes are recorded and discussed. In part two, x-ray diffraction analyses are reported for a series of eleven-membered ring structures and their conformations are correlated to the molecular mechanical results. Molecular mechanics calculations are employed to locate the Global Minimum Energy Conformation (GMEC) of cycloundecane and those conformations within 20 kcal. /mole of this GMEC. The results predict the existence of fourteen minimum energy conformations of cycloundecane - the first ten of which have strain energies differing by 3 kcal/mole or less. The GMEC, cycloundecane 1, is calculated to be only 0. 49 kcal/mole lower in energy than the next conformer, cycloundecane 2. It is concluded that at room temperature cycloundecane is a mixture of several conformations. The calculated low energy conformations of cycloundecane are compared with x-ray results and conformations predicted by other force field calculations. Comparisons are also made of cycloundecane 1 and 2 and the low energy conformations reported for cyclononane, cyclodecane and cyclododecane rings. Introduction of a trans double bond into the cycloundecane conformations results in favourable changes in Baeyer, Pitzer and van der Waals strain. The predicted lowest energy cycloundecene conformer is observed experimentally in the crystal structure of dimethyl (8'-dimethylaminonaphthyl) ammonium dihydrogen tris(cycloundec-l-ene carboxylate) and bears a strong resemblance to the eleven-membered ring conformation observed in zerumbone 2, -dinitrophenylhydrazone. The results of the x-ray analyses of these compounds are recorded and discussed in the second part of this thesis. Two new x-ray diffraction studies on cycloundecane derivatives are also introduced in part two. These are cycloundecylmethyl 3,5-dinitrobenzoate and cycloundecylmethyl - naphthylurethane. Both crystal structures exhibit disorder and it is concluded that the disorder arises from the presence of more than one conformation for the eleven-membered rings. Molecular mechanics calculations on the disordered rings result in model conformations with reasonable geometry and which correspond to cycloundecane 2.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1981
Depositing User: Enlighten Team
Unique ID: glathesis:1981-77177
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 11:53
Last Modified: 14 Jan 2020 11:53
URI: http://theses.gla.ac.uk/id/eprint/77177

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