Cis-3,4-Dimethyl-2-pentene

Figure 6. The reciprocals of the primary methyl radical quantum yields in the 184.9 nm photolysis of 2,3(0) and 3,3-dimethyl-l-butene ( ), cis-3-hexene ( ), and 4-methyl-cis-2-pentene ( ) versus the pressure. From Ref. 67.

It was observed that 4,4-dimethyl-2-pentene was more readily oxidized than the saturated hydrocarbon—2,2-dimethylpentane—although the latter gave a significantly larger ion yield. In the case of this olefin, which was used as the stereoisomeric mixture, the cis and trans isomers were equally attacked in terms of hydrocarbon oxidized. 

The same neopentylidene-alkoxo complexes react with cis-2-pentene to give the two initial metathesis products (4,4-dimethyl-2-pentene and 5,5-dimethyl-3-hexene) and catalyze the metathesis of cis-2-pentene to 2-butenes and 3-hexenes. Furthermore, propylene and ethylene appear in the reaction medium as the catalyst deactivates. These latter olefins are formed by rearrangement of the ethylidene and propylidene intermediates, providing the mechanism for the metathesis chain termination step ... 

The energy difference between cis- and rra M-2-butene is about 4 kJ/mol however, the trans isomer of 4,4-dimethyl-2-pentene is nearly 16 kJ/mol more stable than the cis isomer. Explain this large difference. 

Dimethyl-1-pentene 2,3-Dimethyl-2-pentene 2,4-Diinethyl-2-pentene c s-3,4-Dimethyl-2-pentene Ir s-3,4-Dimettiyl-2-pentene cis-4,4-Dimettiyl-2-pentene af s-4,4-Dimelhyl-2-pentene... 

The difference between the heats of combustion of cis- and ma r-2-butenes is about 4.2 kj mole", but the difference between those of cis- and rmw-4,4-dimethyl-2-pentenes is about 16 kJ mole. Explain why these two values differ significantly. 

Methyl-2-pentene afforded the expected products, 2-butene and 2,5-dimethyl-3-hexene, a highly hindered olefin. (The equilibrium cis content of an equilibrated mixture of 2,5-dimethyl-3-hexene isomers was independently established to be 7% cis.)... 

With these guidelines, the results from the metathesis of 4-methyl-2-pentene now appear to be reasonably accountable for. Most importantly, the lack of formation of c7s-2,5-dimethyl-3-hexene indicates that cis- 1,2-diisopropyl-substitution on the ring is highly unfavored, and trans-1,2-substitution leading to adjacent equatorial substituents is acceptable ... 

The moderate specificity for forming m-2-butene initially (see Fig. 1) is again consistent with equatorial orientation of isopropyl the rather low cis specificity indicates only a moderate preference for equatorial orientation of the a-methyl, probably because of the offsetting weak repulsions caused by cis- 1,2-dimethyl-substitution. This effect is absent in the metathesis of tra i-4-methyl-2-pentene, and trans specificity for... 

Dimethyl-1 -pentene 4.4- Dimethyl-1 -pentene 2.4- Dimethyl-2-pentene cis-4,4-Dimethyl-2-pentene frara-4,4-Dimethyl-2-pentene 2,7-Dimethylphenanthrene 4,5 -Dimethy lphenanthrene 9,10-Dimethylphenanthrene 2,3-Dimethylphenol 21.02... 

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... 

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