The aim of this work was to detect whether non-classical electron delocal1zation would occur between a negative charge situated at the.he 7-position of bicyclo (2,2,1) compounds or the 9-position of bicyclo (4,2,1) compounds and double bonds situated in other parts of systems of these types. . The method chosen for detection of such interactions was comparison of the rates of removal of protons, from those positions, in bicyclic compounds with and without olefinic bonds. In order to labilize the protons at the 7- and 9-positions it was decided to synthesize compounds with phenyl substituents at these po1nts. The key compounds required were 7.-phenylnorbornadiene and 9-phenylbicyclo (4.2.1) nonatrtene. The first was synthesized by a known route without difficulty and from it 7-phenlmorbornane and syn-7-phenylnorbornene. The synthesis of the second occupied the major part of the time available and was finally achieved by a method which was indicated, but not fully described, during the course of the work. Two earlier alternative methods failed. The rates of exchange of the benzylic protons of 7-phenynorbornane and cymene, used as an acyclic comparison, were measured and upper limits set on the rates of exchange of 7-phenylnorbornadiene and seen -7 – phenylnorbornene. At 110o the rates of exchange of the benzylic protons of 7-phenylnorbornadiene and syn-7-phylnorbornene are at 1 ast 140 and 260 times respectively less than that of 7-pheylnorbornane at the same temperature. Although these rate differences are in agreement with prediction of destabilizing non-classical interactions in compounds of this type they are not sufficiently great to prove it. An alternative explanation is that introduction of double bods into the norbornane skeleton increases the strain energy of the molecule and decreases the stabilization of the carbanion by conjugation with the phenyl group ; which would require a further increase in strain energy. In the case of 9-phenylbicyko (3.2.1) nonatriene to appears that treatment with highly basic medium causes several complex changes, probably involving the removal of the benzylic proton at a greater rate than that of cymene. On the basis of the strain energy argument it would be expected that the rate of removal of the benzylic proton form the compound would lie between the rates of sumene and 7-phylnorborane. Further experiment in the system may yield less equivocal information than the experiments of the bicycle (2.2.1) systems. A stabilizing interaction is predicted for anions of this type and hence reduction to the bicyclomonane should cause a diminution of the rate of removal of the benzylic proton. The strain energy argument would predict an increase in the rate of benzylic proton abstraction on hydrogenation to the bicyclononane.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:594885 |
| Date | January 1969 |
| Creators | Nicholson, Peter J. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/71503/ |
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