5- Methyl-cis-2-hexene

The CH3 and CH2 scissors vibrations near 1465 and 1380 cm" are not perturbed to any great extent when the CH3 or CH2 group is adjacent to a double bond. For example, in Figure 5-7 the spectrum of 3-methyl-cis-2-hexene is presented. The two scissors vibrations at 1465 and 1380 cm" are quite distinct. 

These intrazeolite singlet oxygen ene reactions have synthetic potential because the cis effect observed in solution is suppressed in the zeolite [13]. Consequently, allylic hydroperoxides which are inaccessible by other routes may be available via this new technology. For example, photo-oxidations of aryl-substituted alkenes, 7, in sensitizer-doped NaY react to generate the allylic hydroperoxides as the major or exclusive product [17]. In contrast, in solution, the hydroperoxides are formed in only 5-20% yields, with 2-1-2 and 4-1-2 adducts dominating the reaction mixtures. In the case of 2-methyl-5-phenyl-2-hexene, 8, the regio-selectivity for 8b and 8c improved from 47% to 94% and the diastereoselectivity from 10% to 44% as the reaction is moved from solution into the zeolite [18] ... 

There are four pairs of 1- and 2-alkenes with branching in a substituent group for which we can examine double bond migration enthalpies49 4-methyl-l- and 4-methyl-2-pentene 5-methyl-1- and 5-methy 1-2-pentene 4-methyl-l- and 4-methyl-2-hexene and 4,4-dimethyl-1- and 4,4-dimethyl-2-pentene. Each of the 2-enes exists in cis and tram forms. The first two pairs, which are homologous, have Ci to trans-C2 isomerization enthalpies of ca —13 (for two measurements of trans-4-methyl-2-pentene) and —14.4 kJmol-1, and Ci to cis-C2 isomerization enthalpies of —9.6 and —10.4 kJmol-1. The third pair, not homologous with any other, has a Ci to trans-C2 isomerization enthalpy of... 

The effect of the side-chained alkyl group on the cis/trans ratio in the cyclization must be considered. For example, the effects of a methyl group, 2-methyl, 3-methyl, and 4-methyl, in the cyclization of the 5-hexen-l-yl radical is shown in eq. 3.4. The main cyclization product of the 2-methyl-5-hexen-l-yl radical is a trans isomer, that of... 

Few examples are reported for the cyclization of 5-alkenols to 2,3-disubstituted tetrahydro-2//-pyrans where the stereoselectivity depends on the nature of the allylic substituent. The cyclization of 4-methyl-5-hexen-l-ol (1), performed with phenylselenyl triflate in dichloromethane at — 78 "C, proceeds with low 1,2-asymmetric induction and the corresponding tetrahydro-2//-pyran 2 is recovered in 85% yield as a 66 34 (Ircms/cis) diastereomeric mixture19. 

The ratio of isomerization to hydrogenation of /raws-2-hexene and of 4-methyl-l-])entene on amorphous and on microcry.stalline catalysts activated at 400° followed the same pattern as that of 1-hexene (Section VI1,E). Cis-trans isomerization was 5 to 10 times as fast as double-bond migration in runs with /mws-2-hexcne. 

Fig. 5-2. Plot of relative disappearance rates for hydrocarbons observed in smog chambers versus OH rate coefficients (in units of cm3/molecules s) from independent measurements. Key (1) n-butane, (2) isobutane, (3) n-pentane, (4) isopentane, (5) n-hexane, (6) 2-methylpen-tane, (7) 3-methylpentane, (8) cyclohexane, (9) ethane, (10) propene, (11) 1-butene, (12) isobutene, (13) ds-2-butene, (14) frans-2-butene, (15) 1-pentene, (16) methyl-l-butene, (17) cis-2-pentene, (18) 1-hexene, (19) 3,3-dimethylbutene, (20) cyclohexene, (21) toluene, (22) o-xylene, (23) m-xylene, (24) p-xylene, (25) 1,2,3-trimethylbenzene, (26) 1,2,4-trimethylben-zene, (27) 1,3,5-trimethylbenzene. Open circles from Wu el al. (1976) relative to c/s-2-butene, upper scale hatched circles from Lloyd etal. (1976) and Pitts eial. (1978) relative to n-butane, lower scale.

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