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Summary: Pyrolysis Chemistry of Cubane and Methylcubane: The Effect of Methyl Substitution on
Stability and Product Branching
Zhi Li and Scott L. Anderson*
Department of Chemistry, UniVersity of Utah, 315 S. 1400 E., Rm 2020, Salt Lake City, Utah 84112
ReceiVed: December 10, 2002
Pyrolysis reactions of cubane and methylcubane were studied in a micro-flow tube reactor from room
temperature to 1000 K. The composition of the flow tube eluent was probed by chemical ionization, followed
by analysis in a tandem, guided-beam mass spectrometer. It was found that cubane and methylcubane have
nearly identical breakdown temperature dependence, suggesting that methyl functionalization has minimal
effect on the stability of cubane cage bonds. There is, however, a substantial effect of the methyl group on
product branching, resulting in more stable isomers at intermediate temperatures, and a propensity to eliminate
fragments containing the methyl group at high temperatures. Ab initio calculations performed to aid
interpretation are discussed, along with possible mechanisms.
I. Introduction
Highly strained hydrocarbons are an interesting class of
organic molecules, both from a fundamental perspective and
because they have potential as high-energy-density materials.
The high volumetric energy density arises mostly from the fact
that these materials tend to be denser than normal hydrocarbons;
however, the built-in strain energy raises the possibility of
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