Kinetic and equilibrium study of the 2,3-furan ortho-quinodimethane - 4,5-dihydrocyclobuta[b]furan and 9,10-phenanthrene ortho-quinodimethane - 1,2-dihydrocyclobuta[l]phenanthrene interconversions and related studies
Date of Award
Doctor of Philosophy
Walter S. Trahanovsky
Preparation of 4,5-dihydrocyclobuta(b) furan (I) and 4-tert-butyl-4,5-dihydrocyclobuta(b) furan (II) was achieved by irradiation ([lambda]>280 nm) of 2,3-dimethylene-2,3-dihydrofuran (III), and 2-methylene-3-tert-butylmethylene-2,3-dihydrofuran (IV), respectively. Compounds I and II were characterized by [superscript]13C NMR, [superscript]1H NMR, and IR spectroscopy. Diagnostic IR absorptions for 4,5-dihydrocyclobuta(b) furan (I) corresponded with published values. Kinetic analysis of the conversion of I to III (E[subscript] a = 24.4 kcal/mol; log A = 10.1 s[superscript]-1), and II to IV (E[subscript] a = 28.0 kcal/mol; log A = 13.4 s[superscript]-1) was performed by [superscript]1H NMR in benzene-d[subscript]6. Samples were degassed by the freeze-thaw method and sealed in an NMR tube prior to use. The enthalpy difference between I and III and between II and IV was investigated by pyrolyzing precursors to III and IV. Using a [delta]S° determined for the o-xylylene-benzocyclobutene interconversion it was determined that I was at least 4 kcal/mol less stable than III and that II was at least 5 kcal/mol less stable than IV. The larger [delta]H[superscript]\ddagger for II is attributed to destabilization of the transition state by the tert-butyl substituent;Preparation of 1,2-dihydrocyclobuta(l) phenanthrene (V) was achieved by irradiation ([lambda]>280 nm) of 9,10-phenanthrene o-quinodimethane (VI) in solution in much higher yield than previously reported. Kinetic analysis of the conversion of V to VI (E[subscript] a = 34.7 kcal/mol; log A = 13.2 s[superscript]-1) was performed using the method employed for I and II. The rate constants for the conversion of V to VI were verified through trapping experiments using N-phenylmaleimide as the dienophile. The interconversion between VI and V was studied by the thermolysis of V in dilute solution of benzene-d[subscript]6 (K[subscript] eq = 1) using [superscript]1H NMR analysis. Verification of K[subscript]eq was made by the pyrolysis of V, and 10-methyl-9-phenanthrylmethyl benzoate. The [delta]H° for VI and V was calculated with the method used for the furan systems. Energy profiles for the interconversion between VI and V and between o-xylylene and benzocyclobutene were compared, and differences were explained using Dewar Resonance Energies;Irradiation ([lambda]>220 nm) of 2-methyl-3-ethenylfuran led to an unsymmetrical dimer with one or possibly two acetyl groups.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Craig Wilson Montgomery
Montgomery, Craig Wilson, "Kinetic and equilibrium study of the 2,3-furan ortho-quinodimethane - 4,5-dihydrocyclobuta[b]furan and 9,10-phenanthrene ortho-quinodimethane - 1,2-dihydrocyclobuta[l]phenanthrene interconversions and related studies " (1990). Retrospective Theses and Dissertations. 9864.