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Theoretical studies of organic diradicals and the thermal rearrangement of bicyclopropenyls

Citation

Davis, James Hubbard (1977) Theoretical studies of organic diradicals and the thermal rearrangement of bicyclopropenyls. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:04242012-160948000

Abstract

Part A. Generalized valence bond calculations on cyclopropene and vinylmethylene lead to the following conclusions: (1) the allyl-type π-system is strongly distorted by the presence of the unpaired sigma electron leading to a methylene-like triplet, ^3A^", but a 1,3-diradical-like singlet state, ^1A^"; (2) the lowest-lying singlet state of vinylmethylene has the form of a singlet methylene ^1A lying 12 kcal/mole above the triplet ground state, while the diradical singlet state lies at 14 kcal/mole.

Part B. Generalized valence bond calculations on trimethylenemethane indicate that the ground state is the planar triplet with the planar singlet state 26 kcal/mole higher. The rotational barrier for the triplet state is 18 kcal/mole, while one component of the planar singlet prefers the bisected geometry by 7 kcal/mole. Oscillator strengths for vertical transitions and ionization potentials are also reported.

Part C. Generalized valence bond calculations on vinylidene predict that the ground state is a singlet with a methylene-like triplet at 2 eV higher. With extensive CI calculations, we find CC bond energy of D_0(h_2C=C) = 150.1 kcal/mole and a heat of formation of 111.5 kcal/mole at 298°K. The dipole moment for the singlet is calculated to be 2.23D, while the dipole moment for the triplet is 0.55D.

Part D. Generalized valence bond calculations on aminonitrene indicate that the ground state is a singlet (^1A_1) with a low-lying triplet state (^3A_2) at 15 kcal/mole. We find the nitrogen-nitrogen bond dissociation energy for the singlet state is 70.4 kcal/mole. The dipole moment is found to be 4.036D for the ^1A_1 and 2.351D for the ^3A_2 state of aminonitrene. The ionization potential is calculated to be 9.4 eV.

Part E. The kinetic distribution of isomeric xylenes formed on the thermal aromatization of dl- and meso-1,1'-dimethyl-3,3'-bicylopropenyl and of 3,3'-dimethyl-3,3'-bicyclopropenyl has been determined by extrapolation of the time-dependent xylene percentages to zero percent conversion. The data is most consistent with a mechanism involving initial cleavage of one of the cyclopropene rings, followed by expansion of the other ring, closure to Dewar benzene and finally opening of the Dewar to form aromatic products.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Bergman, Robert G. (advisor)
  • Goddard, William A., III (co-advisor)
Thesis Committee:
  • Unknown, Unknown
Defense Date:6 August 1976
Record Number:CaltechTHESIS:04242012-160948000
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:04242012-160948000
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6970
Collection:CaltechTHESIS
Deposited By: Benjamin Perez
Deposited On:02 Nov 2012 20:45
Last Modified:26 Dec 2012 04:42

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