Methylhexane, ring closure

Methyl groups, as hydrocarbon surface species, vibrational spectra, 42 214—219 Methylheptane, ring closure, 25 154 3-Methylhexane dehydrocyclization, 30 13 isomerization, 30 7, 14, 39-40 Methylhexane, ring closure, 25 155 Methyl hydroperoxide, catalytic decomposition, 35 161... 

Metallocarbene formation by hydrogen shift explains the observed selectivity in the 1,5-dehydrocyclization of 3-methylhexane on Pt/AljOj (41). Three cyclic intermediates may be formed from this molecule, 1,2-dimethylcyclopentane (4), 1,3-dimethylcylopentane (5), and ethylcyclopentane (6). By using several selectively C-labeled 3-methylhexanes, the contribution of each parallel pathway both in cyclic type isomerization and in dehydro-cylization to gaseous cyclic molecules was determined. Relative rates of 3 2 1 were observed for 1-5, 2-6, and 6-7 ring closure (giving 5, 4, and 6, respectively) (Scheme 49 and Table VII), whatever the dispersion of the platinum (2-10%) and the temperature (32O°-38O°C). 

The formation of wetn-labeled toluene can be explained neither by direct 1-6 ring closure, nor by cyclic-type isomerization of n-heptane to 3-methylhexane followed by 1-6 ring closure of the latter (94). We suggest that the abnormal aromatization process responsible for the formation of meta-labeled toluene is initiated by a dicarbene as in the nonselective mechanism A (see Section IV, Scheme 47). Aromatization is not influenced by the dispersion of the platinum on the support (758), so that it may be assumed that aromatization involves a single metal atom. Isomerization of the dicarbenes (7) to the dicarbenes (8) via rt-adsorbed cyclopentanes, followed by isomerization to the suitable carbene-olefin species (9), would result in 1-6 ring closure and aromatization (Scheme 69). 

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