Cope and 1,3-allylic rearrangements and ring closure of the 1,5-hexadiene radical cation prior to decomposition in the gas phase

Journal Article · Fri Aug 13 04:00:00 EDT 1982 · J. Org. Chem.; (United States)

DOI:https://doi.org/10.1021/jo00138a034· OSTI ID:6388617

Wolkoff, P ^[1]; Holmes, J L

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1. Univ. of Copenhagen, Denmark

The chemistry of neutral 1,5-hexadiene (1) has been studied extensively. It undergoes the well-known (degenerate) Cope rearrangement under thermal conditions. Facile transformations occur upon irradiation, and depending on the photochemical conditions allylcyclopropane and bicyclo(2.1.1)- and (2.2.0)hexane may be formed. Isotopic separation of deuterated 1 in favor of deuterium situated in the external vinyl sites has been demonstrated with infrared laser; deuterium in the allylic positions, however, is favored under thermal conditions. In contrast, recent electron impact studies xDdicate a chemical inertness of the radical cation of 1 (1/sup +/.). It was shown by photodissociation spectroscopy that 1/sup +/in equilibrium remains as an unconjugated diene at low internal energies. Comparison of the heat of formation of C/sub 5/H/sub 7//sup +/ions formed by CH/sub 3/. loss from isomeric C/sub 6/H/sub 10/ radical cations (ions of m/z 67 give rise to base peak in the normal mass spectra of C/sub 6/H/sub 10/ isomers) and the kinetic energy release (T) associated therewith showed that 1/sup +/in equilibrium among its linear isomers forms the cyclopentenyl cation with the lowest excess energy and smallest T value. This result is in accord with the photodissociation results insofar as 1/sup +/in equilibrium among its linear isomers forms the cyclopentenyl cation with the lowest excess energy and smallest T value. This result is in accord with the photodissociation results insofar as 1/sup +/in equilibrium cannot isomerize to another linear diene prior to decomposition. The collisional activation mass spectra of C/sub 6/H/sub 10/ isomers confirmed that nondecomposing 1/sup +/in equilibrium has no or only little resemblance with the radical cations of 1,3-, 1,4-, and 2,4- hexadiene, cyclohexene, and 1-methylcyclopentene. In light of the apparent retention of structure of 1/sup +/in equilibrium, this work is concerned with how the cyclopentenyl cation is formed.

• OSTI ID: 6388617
• Journal Information: J. Org. Chem.; (United States), Journal Name: J. Org. Chem.; (United States) Vol. 47:17; ISSN JOCEA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
CHEMICAL REACTIONS
DATA
DEUTERATION
DIENES
EXPERIMENTAL DATA
HYDROCARBONS
INFORMATION
LABELLED COMPOUNDS
NUMERICAL DATA
ORGANIC COMPOUNDS
POLYENES
STRUCTURAL CHEMICAL ANALYSIS