2,3-Dimethyl-2-pentene

The initiation step for metallocarbyne catalyst precursors is not well-understood. But, in the case of Re, a well-defined metallocarbene, the initiation products have been detected 0.7 equiv. of a 3/1 mixture of 3,3-dimethylbutene and 4,4-dimethyl-2-pentene (Fig. 2) [81,82]. 

Fig. 2 Quantification in the gas phase of 3,3-dimethylbutene and 4,4-dimethyl-2-pentene during propene metathesis (500 equiv.) catalyzed with 13(1 equiv.) at 25 °C...

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... 

Figure 3.27 Quantification 3,3-dimethylbutene and ( )-4,4-dimethyl-2-pentene during propene metathesis catalyzed by i-0-Re( Bu)(=CH Bu)(CH 2Bu) at 25 C.

Note also that, in contrast to classical heterogeneous catalysts, the initiation step of [=SiORe(=CtBu)(=CHtBu)(CH2tBu)] is well defined and corresponds to the cross-metathesis of the alkene with the neopentyhdene ligand. In fact, in the metathesis of propene, 0.7 equiv of a 3 1 mixture of 3,3-dimethyl-l-butene and 4,4-dimethyl-2-pentene is formed (Figure 3.27) the nearly quantitative formation of cross-metathesis products is consistent with a real single-site catalyst. Moreover,... 

C, no solvent). The grafted catalyst proved to be highly active, with equilibrium reached in less than Ih. A TOP of 0.25molmoT s was attained, which corresponds to one of the best rates observed for a Re metathesis catalyst. Also observed during the metathesis reaction was the evolution of approximately 1 equivalent of a 1 3 mixture of 3,3-dimethylbutene and 4,4-dimethyl-2-pentene, which arises from the cross-metathesis of the neopentyl ligand of the grafted complex and propene. 

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. 

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... 

Z)-4,4-Dimethyl-2-pentene 4650 kJ/mol (1111.4 kcal/mol). Disubsti-tuted double bond, but destabilized by van der Waals strain. 

A-14. Compound A, on reaction with bromine in the presence of light, gave as the major product compound B (C9H19Br). Reaction of B with sodium ethoxide in ethanol gave 3-ethyl-4,4-dimethyl-2-pentene as the only alkene. Identify compounds A and B. 

If we start numbering the carbon atoms from the left hand side, the name of the compound comes out to be 4,4—dimethyl-2-pentene. The given name is incorrect. 

Use SpartanBuild to construct E and Z isomers of 4,4-dimethyl-2-pentene, and minimize the energj of each. Which isomer has the lower energy Compare the C-C=C bond angles in each, and explain how each shows strain. 

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