The Synthesis of Polar Substituted Norbornenes and the Study of their ¹³C Chemical Shift and Stereoelectronic Properties.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis represents an attempt to investigate the mode of operation of electronic effects on the C=C bond in 5-substituted-2-norbomenes. A total of 14 exo and 9 endo derivatives were prepared for study. In the first instance their 13C NMR spectra were obtained, and the effects of these substituents on the chemical shifts of the two alkene carbon atoms were investigated. The role of the polar and resonance effects of the substituent in influencing these by polarising the π electrons of the double bond was explored. It was found that the polar effect of the substituent distorted the π system; but that although -I substituents led to a build up of electron density on the nearer of the two carbons as expected, this build up was less than expected and suggested that part of the charge was being delocalised into the saturated norbomyl framework in some way. Attempts to correlate substituent effects with Hammett substituent constants of various types were unsuccessful. Next the regiochemistry of the addition of phenylselenenyl chloride to the same alkenes was studied. The ratio of the addition products formed was found to be controlled by the electronic nature of these substituents, although in the case of the endo substituted compounds steric effects appeared to play an important role in some cases. Lastly, the ability of the double bond in 2-norbomene to interact with a C5-X bond was investigated by measuring the effect on the length of the C-X bond by X-ray diffraction. A series of derivatives where X was a good leaving group (nucleofuge) was prepared and their structures were determined. It was hoped to show that the C-X bonds were longer when X was exo than when it was endo, indicating that the bond in the first had been weakened by the π bond of the alkene interacting with the back orbital of the C-X bond. Unfortunately the crystals showed considerable disorder, and this affected the reliability of the bond lengths obtained to such an extent that the results obtained proved inconclusive.