By M.P. CAVA and M.J. MITCHELL (Eds.)
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The molecular constitution hypothesis--that a molecule is a suite of atoms associated by way of a community of bonds-- presents the vital technique of ordering and classifying observations in chemistry. despite the fact that this speculation isn't really similar on to the physics which governs the motions of atomic nuclei and electrons.
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CYCLOBUTADIENE 1. , tricyclooctadienes or products of their thermal rearrangement) under conditions which should be conducive to the generation of monomeric cyclobutadienes. The dimerization of a triplet cyclobutadiene species by cycloaddition is a process which undoubtedly is energetically favorable and leads to the formation of two new σ bonds without requiring spin inversion. Maximum overlap of π orbitals should be energetically favorable in the transition state of the dimerization (as it is in the Diels-Alder reaction), resulting in the formation of syn tricyclooctadienes (A).
In addition, tautomer (38) was transformed in several steps into a diketone (57) which was synthesized by an independent route. 1 50 No direct evidence regarding the configuration of dimers (35a) and (35b) is available as yet. f Subjecting dimethiodide (55) to Hofmann elimination in refluxing ter/-butyl * In this connection it is interesting to note that the sterically hindered analog of (29), l,l,4,4,5,5,8,8-octamethyl-l,2,3,4,5,6,7,8-octahydrobiphenylene, appears to undergo hydrogen abstraction and rearrangement reactions but not dimerization.
86 Interestingly enough, the preparation of difluoroacetylene has been claimed in two p a t e n t s 7 7' 1 13 and in one of these the isolation of a fluorocarbon, C 4 F 4 , possibly tetrafluorocyclobutadiene (58) was r e p o r t e d . ) on standing in the gaseous state at room temperature for several hours. 1 13 * When the dehalogenation of 1,2-dibromocyclohexene with sodium in ether was carried out in the presence of 1,3-diphenylisobenzofuran, an adduct of cyclohexyne was formed (Gwynn, 1962, ref.
Cyclobutadiene and Related Compounds by M.P. CAVA and M.J. MITCHELL (Eds.)