Date of Award
Program or Major
Doctor of Philosophy
Richard P Johnson
The potential energy surface of linear hydrocarbons has been extensively investigated by experiments and the use of molecular modeling. Linear C4 structures have demonstrated the potential to scramble their inner carbon atoms leading to the formation of novel strained intermediates.
Long-range carbon atom topomerization in a 1,3-diyne has been demonstrated for the first time. 1-Phenyl-4-p-tolyl-1,3-butadiene, 13C enriched at C-1, was synthesized and subjected to flash vacuum pyrolysis. Under high temperature and at low pressure, this resulted in nearly complete 13C label equilibration among all of the sp hybridized carbons, as seen by NMR analysis. It has been proposed that 1,3-diynes rearrange to form several unprecedented strained intermediates in order to support carbon transpositions. As investigated computationally, 1,3-butadiene forms trialene, (bicyclo[1.1.0]-1,3-butadiene), a highly strained organic intermediate. Trialene serves as a key intermediate in the long-range carbon scrambling. Density functional (B3LYP/6-311+G(2d,p)), and Moller-Plesset, theory calculations support the possible formation of trialene.
Long-range carbon topomerization in butatrienes has been investigated as well. Density functional and Moller-Plesset theory calculations predict a low-energy pathway that leads to carbon scrambling of the inner sp hybridized carbons of butatriene. We predict a thermal rearrangement of butatriene to form methylenecyclopropylidene, followed by carbene insertion to form bicyclo[1.1.0]but-1(3)-ene. Ring opening and reformation of butatriene is an overall degenerate process that leads to carbon scrambling. All of these structures have been found computationally as true energy minima along this reaction pathway. Control pyrolysis experiments with tetraarylbutatrienes have established compound stability up to approximately 800°C. A suitable synthesis of 13C labeled unsymmetrical butatriene and pyrolysis experiments are needed in order to support our calculations.
Mabry, John, "Thermal rearrangements of linear carbon chains: Theoretical and experimental studies" (2003). Doctoral Dissertations. 195.