The UV Photoelectron Spectroscopy of Transients, an Experimental and Computational Investigation of Electronic Structure and Reaction Mechanisms

Abstract

<p>A test study of the vacuum thermolysis of phenyldiazoethane has shown the ability to generate a diazo compound from the respective sodium salt. It has also illustrated the utility of using a CW CO2 laser as a directed heat source to thermolize a diazo compound and record the PE spectrum of the pyrolysate. The spectrum of styrene was successfully recorded upon the thermolysis of phenydiazoethane in the source chamber of the PE spectrometer.</p> <p>Photoelectron spectra of possible precursors to the elusive cycloheptatetraene were recorded. Thermolyses of these precursors were performed in the source chamber of the PE spectrometer and PE spectra of their thermolysates were recorded. Calculations of ionization potentials and simulation of partial PE spectra of possible products of the thermolysis were employed in order to attempt to assign the observed experimental ionization potential bands. Although a clear PE spectrum of cycloheptateraene could not be obtained, the thermolysis experiment has shown IP bands belonging to fulvenallene, which is the lowest energy isomer on the C7H6 potential energy surface. A PE spectrum of bicyclo[3.2.0]hepta-1,3,6-triene was recorded and its ionization potentials were assigned relative to calculated values. Although this triene is considered as a key intermediate on the C7H6 potential energy surface it was not detected in the pyrolysis of 2-diazobicyclo[3.2.0]hepta-3,6-diene.</p> <p>Thermolysis of bicylo[3.2.0]hept-6-en-2-one has made it possible to record a PE spectrum of a transient cyclohepta-2(Z),4(E)-dien-1-one. PE spectra of both ketones were recorded for the first time. The thermolysis has also illustrated that the ring openin gof the cyclobutene moiety follows the conrotatory path in accord with the Woodward-Hoffmann rules despite the small size of the ring adjoined to the cyclobutene. A PE spectroscopic, thermolysis and computational investigation of N,N-bicyclo[3.2.0]hepta-3,6-dien-1-amine has illustrated the ability of E,Z,Z transient isomer to rearrange through a trans-cis isomerisation to yield a thermodynamically more stable product.</p> <p>An investigation of 7-subsituted cycloheptatrienes has shown that most cycloheptatrienes favor the substituents in the equatorial position. The only compound that has been identified with PE spectroscopy to prefer the substituent in the axial position was the methylthiocycloheptatriene.</p>