Physico-Chemical Studies of Some Organic Molecules

Porte, Andrew L (1957) Physico-Chemical Studies of Some Organic Molecules. PhD thesis, University of Glasgow.

Abstract

This thesis describes investigations of the molecular structures of a number of organic compounds using physicochemical methods. Two main methods are employed. These are 1) Methods of X-ray structural analysis. 2) Theoretical methods (molecular orbital calculations). Three compounds are considered under the first heading. These are a) Tiglic Acid b) Angelic Acid c) Tetrabenzo-2:3-6:7-2':3,-6':7'-heptafulvalene. Tiglic and angelic acids are cis-trans isomers which were known from chemical evidence to have the formula (formula redacted) However, chemical methods of deciding which acid is the cis and which is the trans isomer were based on results which, by themselves, were of doubtful value although when considered collectively indicated the trans structure for tiglic acid and the cis structure for angelic acid. X-ray analyses of both acids are described in the thesis. A novel method of distinguishing between cis and trans isomers by means of molecular Fourier transforms, which may be applicable in the case of planar molecules is described. Unit cell and space group data are given for both compounds and a complete and accurate analysis of tiglic acid is described. This analysis shows tiglic acid to be the trans acid I (formulas redacted) thereby confirming the formula usually accepted - although not proved - for this acid. Owing to various experimental difficulties the analysis of the angelic acid structure is not as accurate as that of tiglic acid, but the work confirms the formula II for the acid. The complete determination of the structure of angelic acid has been hindered somewhat by unusual difficulties involving homometric projections. Work is still proceeding on the compound and it is believed that the described solution of the problem is essentially correct. Three dimensional analysis at low temperatures may be necessary to achieve high accuracy. The thesis also describes some work carried out on Tetrabenzo-2:3-6:7-2':3'-6':7'-heptafulvalene (III). If a planar model of this molecule is built up using aromatic bond lengths of 1.4A., and assuming rings A and B to be regular heptagons and rings C, D, E and P to be regular hexagons, then it is found that the starred carbon atoms approach to within about 1.3A. of one another. Such a close distance of approach is impossible and so the atoms of the molecule cannot be coplanar. The object of the work on this compound was to find the actual shape of the molecule. Unit cell and space group data for III are described in the thesis and a discussion on the probable conformation is given. This part of the work is not yet finished but the structure postulated is chemically reasonable and fits in with a number of experimental observations. The second type of method used in the investigations was the application of molecular orbital theory. By this means, pi-electron distributions, bond orders, and bond lengths for pteridine(IV) have been derived. A new bond order-bond length curve for carbon-nitrogen bonds is proposed.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Molecular chemistry, Organic chemistry, Physical chemistry
• Date of Award: 1957
• Depositing User: Enlighten Team
• Unique ID: glathesis:1957-79210
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 05 Mar 2020 11:28
• Last Modified: 05 Mar 2020 11:28
• URI: https://theses.gla.ac.uk/id/eprint/79210