Methylbut-l-ene

2-Methylbut-l-ene.— Thermodynamic functions for all the pentenes were originally calculated by an incremental method from data for the lower mono-olefins. Later, experimental values of the entropy and heat capacity were used in a statistical calculation which exemplifies the treatment necessary for several molecules. 

Conversion of 3-methylbut-l-ene into 2,5-dimethylhex-3-ene, reaction (7), has been achieved using a Re207/Al203 catalyst (2 h at 20°C) with good yield (58%) 

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Polyolefins with branched side chains other than P4MP1 have been prepared Figure 11.14). Because of their increased cohesive energy, ability for the molecules to pack and the effect of increasing chain stiffness some of these polymers have very high melting points. For example, poly-(3-methylbut-l-ene) melts at about 240°C and poly-(4,4-dimethylpent-l-ene) is reported to have a melting point of between 300 C and 350°C. Certain cyclic side chains can also... 

A most interesting case is 3-methylbut-l-ene. At about -80 °C it gives high polymers with the expected structure (III) ... 

The rearrangements of 3-methylbut-l-ene oxides" and l,2-epoxybut-3-ene on lithium phosphate have been studied, and a detailed theoretical study of the rearrangement of allene oxide (342) to cyclopropanone (344), which shows that the transformation proceeds via an intermediate oxyallyl (343), has been presented. It has been shown that aldehydes, ketones, and cyclic ethers are all produced... 

Similar reaction of 3-methylbut-l-ene with HCl gives ronghly eqnal amounts of two isomeric... 

The all-trans-all-isotactic and all-trans-all-syndiotactic structures for the 1,4-polymerization of 1,3-pentadiene are shown in Fig. 8-6. In naming polymers with both types of stereoisomerism, that due to cis-trans isomerism is named first unless it is indicated after the prefix poly. Thus, the all-trans-all-isotactic polymer is named as transisotactic l,4-poly(l,3-penta-diene) or isotactic poly( -3-methylbut-l-ene-l,4-diyl). 

While the diphenyl complex affords 59a and 59c, the di-/-butyl derivative undergoes loss of 3-methylbut-l-ene from the intermediate alkynyl complex to give 59b after protonation (76). 

Hydroboration of 3-methylbut-l-ene (15) gives 94% of the primary (16) and 6% of the secondary (17) organoborane, whereas with the 2-methylbut-l-ene (18) essentially only the primary derivative (19) is formed. Hydroboration of 2-methyl-... 

An 11 kJ/mol (2.7 kcal/mol) stability difference is typical between a monosubstituted alkene (but-l-ene) and a trans-disubstituted alkene (frans-but-2-ene). In the following equations, we compare the monosubstituted double bond of 3-methylbut-l-ene with the trisubstituted double bond of 2-methylbut-2-ene. The trisubstituted alkene is more stable by 14 kJ/mol (3.4 kcal/mol). 

The photolysis of methylisopropyldiazirine yields 2-methylbut-2-ene, 3-methylbut-l-ene, and cis- and irans-l,2-dimethylcyclopropane. The pyrolysis yields the same hydrocarbons, though once again in somewhat different relative yields. Again these differences can be rationalized in terms of a vibrationally excited carbene formed by the photochemical reaction. The results are shown in Table III. 

In the photolysis of decreasing pressure, the yield of 2-methylbut-2-ene increases, and a new product 3-methylbut-l-ene is formed. At the lowest pressures investigated, small quantities of 2-methyl but-l-ene were detected. The following mechanism was suggested to explain the experimental data quantitatively. 

At high pressures the mechanism predicts that the only products Avill be 1,1-dimethylcyclopropane, 2-methylbut-2-ene, and nitrogen. At low pressures, depending on the magnitudes of kss, hi, and kta relative to h, there will be increasing quantities of 3-methylbut-l-ene and 2-methylbut-l-ene, and the relative yield of 2-methylbut-2-ene will also increase. With pure teri-butyldiazirine at a pressure of 80 mm., about... 

Table 3. 2-Aryl-l,l-dimethylcyclopropanes by Light-Induced Conversion of 3-Aryl-3-methylbut-l -enes...

All the examples to be discussed are of square-planar platinum(II) complexes, recorded in Scheme 2. Thus Boucher and Bosnich (8) have prepared a series of olefin complexes derived from ( -tolylmethylsulfoxide)dichloroplatinum(II) in which the ligand is S-bonded. The S-methyl protons provide a convenient and sensitive NMR probe for the determination of diastereomer ratios. In the cases of but-l-ene, 3-methylbut-l-ene, styrene and 3,3-dimethylbut-l-ene crystals of a single diastereomer can be isolated in all but the last of these, however, there is rapid equilibration between diastereomers in solution, with relatively little discrimination between them (typically 55-75% of the major species). Since several rotamers are possible in the sulfoxide ligand it is not easy to specify the origin of chiral discrimination. 

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