2- Methyl-2-butene structure

Comparison of experimental and calculated KIE values for 2-methyl-butene is more complicated due to formation of three stereoisomeric/regioisomeric transition structures ... 

NAME 2-Ethyl-3-methyl-1 -butene STRUCTURAL FORMULA... 

Figure 8.8. Adsorbed states of isoprene (2-methyl-1,3-butadiene) as alternative 71 0 structures and their half-hydrogenated states, leading to the three isomeric 2-methyl butenes. - ...

The mam components of a skunks scent fluid are 3 methyl 1 butanethiol and as- and trans-2 butene 1 thiol Write structural formulas for each of these compounds... 

Acyclic C5. The C5 petroleum feed stream consists mainly of isoprene which is used to produce rubber. In a separate stream the linear C5 diolefin, piperylene (trans and cis), is isolated. Piperylene is the primary monomer in what are commonly termed simply C5 resins. Small amounts of other monomers such as isoprene and methyl-2-butene are also present. The latter serves as a chain terminator added to control molecular weight. Polymerization is cationic using Friedel-Crafts chemistry. Because most of the monomers are diolefins, residual backbone unsaturation is present, which can lead to some crosslinking and cyclization. Primarily, however, these are linear acyclic materials. Acyclic C5 resins are sometimes referred to as synthetic polyterpenes , because of their similar polarity. However, the cyclic structures within polyterpenes provide them with better solvency power and thus a broader range of compatibility than acyclic C5s. 

The principal components of the cut are butene-1, butene-2, isobutylene and butadiene-1,3. Methyl, ethyl, and vinyl acetylenes, butane and butadiene-1,2 are present in small quantities. Butadiene is recovered from the C4 fraction by extraction with cuprous ammonium acetate (CAA) solution, or by extractive distillation with aqueous acetonitrile (ACN). The former process is a liquid-liquid separation, and the latter a vapor-liquid separation. Both take advantage of differences in structure and reactivity of the various C4 components to bring about the desired separation. 

Draw Lewis structures for the possible carbocations resulting from protonation of the double bond in 3-methyl-1-butene, and decide which is favored. (Check your result using available energy data for C5H11 carbocations.) What would be the product of bromide addition to the more stable cation Is this the observed product ... 

An unusual dependence of the structure of the reaction product on the acylating agent (catalyst and acyl group) was observed by Balaban and Nenitzeseu in the diacylation of olefins 195, where R = Me (2-methyl-2-butene ) or R = Ph (2-methylpropenyl-benzene ) strong catalysts like AlClg or SbCls promote the formation of the 2,4,6-trisubstituted compound 197, whereas weaker... 

This occurs because 2-butene, itself, can exist in two different structures, the cis-or the trans- configurations, depending on whether the methyl groups are situated on the same side or on opposite sides of the main chain. 

What evidence is there to support the carbocation mechanism proposed for the electrophilic addition reaction of alkenes One of the best pieces of evidence was discovered during the 1930s by F. C. Whitmore of the Pennsylvania State University, who found that structural rearrangements often occur during the reaction of HX with an alkene. For example, reaction of HC1 with 3-methyl-1-butene yields a substantial amount of 2-chloro-2-methylbutane in addition to the "expected" product, 2-chloro-3-methylbutane. 

Most commercial polymers are substantially linear. They have a single chain of mers that forms the backbone of the molecule. Side-chains can occur and can have a major affect on physical properties. An elemental analysis of any polyolefin, (e.g., polyethylene, polypropylene, poly(l-butene), etc.) gives the same empirical formula, CH2, and it is only the nature of the side-chains that distinguishes between the polyolefins. Polypropylene has methyl side-chains on every other carbon atom along the backbone. Side-chains at random locations are called branches. Branching and other polymer structures can be deduced using analytical techniques such as NMR. 

Fig. 10.1. Minimum-energy transition structures for ene reactions (a) propene and ethene (b) propene and formaldehyde (c) butene and methyl glyoxylate-SnCl4 (d) butene and methyl glyoxylate-AlCl3. Reproduced from Helv. Chim. Acta, 85, 4264 (2002), by permission of Wiley-VCH.

Fig. 12.14. Competing cis abstraction and trans abstraction transition structures for hydroperoxide formation 2-methyl-2-butene. Adapted J. Am. Chem. Soc., 125, 1319 (2003), by permission of the American Chemical Society.

Rates of reaction and the course of each step depended upon the structures of the species. With a-methylstyrene and with methallyl chloride, steps (b) and (c) were not detectable perhaps (a) did not happen and the product was that of direct addition with no exchanges or isomerization. With 1-hexene, 3-methyl-1-butene-1,3-methyl-2-butene, and cyclohexene the exchanges and isomerization were much faster than step (d). By step (d) the product left the coordination sphere of the metal and no longer participated in any of the processes. 

In the crystal structures of many other isotactic polymers, with chains in threefold or fourfold helical conformations, disorder in the up/down positioning of the chains is present. Typical examples are isotactic polystyrene,34,179 isotactic poly(l-butene),35 and isotactic poly(4-methyl-l-pentene).39,40,153,247... 

When considering the stability of spin-delocalized radicals the use of isodesmic reaction Eq. 1 presents one further problem, which can be illustrated using the 1-methyl allyl radical 24. The description of this radical through resonance structures 24a and 24b indicates that 24 may formally be considered to either be a methyl-substituted allyl radical or a methylvinyl-substituted methyl radical. While this discussion is rather pointless for a delocalized, resonance-stabilized radical such as 24, there are indeed two options for the localized closed shell reference compound. When selecting 1-butene (25) as the closed shell parent, C - H abstraction at the C3 position leads to 24 with a radical stabilization energy of - 91.3 kj/mol, while C - H abstraction from the Cl position of trans-2-butene (26) generates the same radical with a RSE value of - 79.5 kj/mol (Scheme 6). The difference between these two values (12 kj/mol) reflects nothing else but the stability difference of the two parents 25 and 26. 

Dimethyl-l,3-butadiene underwent reaction to give the expected product 2,3-di-methyl-3-buten-2-ol besides a product containing a rearranged carbon structure, whose formation has been attributed to a radical process occurring during the demercuration step (equation 151). 

To see why this is important, consider a butene (2-butene) in which the double bond is between the two central carbon atoms CH3—CH—CH—CH3. If we think about it for a bit, we can recognize that there are really two of these structures they are stereoisomers that are not enantiomers and not constitutional isomers. Such stereoisomers are termed diastereomers. Diastereomers in this class are also known by the older and largely obsolete term geometrical isomers. They differ in the way that the two methyl groups at the ends of the molecule are disposed with respect to each other. The two possibilities are ... 

---