Bicyclic Compounds Containing Cyclobutane Rings

Relatively few bicyclic compounds containing a cyclobutane ring have been studied kinetically. Bicyclo[2,l,0]hexane has been investigated by Steel et al. (1964) in the temperature range 130-210° C, when the only product is diallyl. The results obtained are fitted by the Arrhenius equation 

The authors suggest the isomerization proceeds via the rupture of the weak bridgehead bond, viz.  

If this is the reaction path, then the biradical is probably not to be thought of as the flat strain-free cyclohexane biradical 

The thermal isomerization of this compound (a valency bond isomer of bicyclo[2,2,0]hexane) is of particular interest. Between 327 and 366° C and at pressures from 0 2 to 20 mm, Srinivasan and Levi (1963) found that this compound isomerized cleanly by a first-order process to give diallyl. 

Addition of nitric oxide and propylene, or increase in the surface-to-volume ratio of the reaction vessel, did not affect the rate of reaction. The data were fitted by the Arrhenius equation 

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XI. Bicyclic Compounds Containing Cyclobutane Rings A. Bicyclo 2,lfi hexane... 

Intramolecular [2 + 2] photocycloaddition of dienes is an important method of formation of bicyclic compounds containing four-membered rings.118 Direct irradiation of simple nonconjugated dienes leads to cyclobutanes.119 120 121 Strain makes the reaction unfavorable for 1,4-dienes, but when the alkene units are separated by at least two carbon atoms, cycloaddition becomes possible. 

Cyclic adj. All cyclic compounds are recognized by their ring structure. Benzene is the simplest and most well-known cyclic compound, consisting of a single ring. Its monocyclic. When two or more rings are involved as with naphthalene, for example, the compound is bicyclic, tricycle, etc. Cyclic compounds may contain from three to six or more carbon atoms in the ring, e.g.. Cyclopropane - three atoms Cyclobutane -four atoms Cyclopentane - five atoms Cyclohexane - six atoms. 

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