Trans but-2-ene

A cycloaddition reaction produces a ring of atoms by forming two new G-bonds, for example the formation of a cyclobutane dimer from two alkene molecules. The direct photoreaction involves the concerted reaction of the singlet Jtpt ) excited state of one alkene with the ground state of the other. Stereospecific reactions in which the dimers preserve the ground-state geometry occur when liquid cis- or trans-but-2-ene are irradiated at low temperature ... 

Figure 15.2 Crosswise arrangement of trans-but-2-ene molecules in ZSM-57 pores giving rise to the formation trans-3,4-dimethylhex-2-ene views along ten-ring (above) and eight-ring (below) channels.

Returning to our example, you will find that there are two geometric isomers of but-2-ene. One is referred to as the cis isomer and the other is the trans isomer. It is important to remember that geometric isomers are different compounds and have distinct physical properties. For example, ds-but-2-ene melts at -139°C, whereas trans-but-2-ene melts at -105°C. 

Related to these elimination processes is the reduction of 1,4-dihalides of trans-but-2-ene in dimethylformamide to yield butadiene [137]. 

The 1,4- and 1,5-benzothiazepines (421) and (423) have been prepared by the photochemical reactions of the benzoisothiazole (420) and the benzothiazole (422) respectively with ethyl vinyl ether (81TL529, 2081). The mechanisms of these reactions are not fully established but it is interesting to note that the reactions of (422) with cis- and trans-but-2-ene are stereospecific. 

Fig. 14. Distribution of the n-butenes as a function of extent of hydrogenation of but-l-ene over palladium—alumina at 37°C [124]. o, But-l-ene , trans-but-2-ene , cis-but-2-ene. Dotted lines indicate thermodynamic equilibrium yields.

Butene trans-But-2-ene (Ge, Al)-X T, chemical shifts, interactions with cations (307)... 

Using a relative rate method, rate constants for the gas-phase reactions of O3 with 1- and 3-methylcyclopentene, 1-, 3- and 4-methylcyclohexene, 1-methylcycloheptene, cw-cyclooctene, 1- and 3-methylcyclooctene, cycloocta-1,3- and 1,5-diene, and cyclo-octa-l,3,5,7-tetraene have been measured at 296 2 K and atmospheric pressure. The rate constants obtained (in units of 10-18 cm3 molecule-1 s-1) are as follows 1-methylcyclopentene, 832 24 3-methylcyclopentene, 334 12 1-methylcyclohex-ene, 146 10 3-methylcyclohexene, 55.3 2.6 4-methylcyclohexene, 73.1 3.6 1-methylcycloheptene, 930 24 d.s-cyclooclcnc, 386 23 1-methylcyclooctene, 1420 100 3-methylcyclooctene, 139 9 d.v.d.v-cycloocta-1,3-diene, 20.0 1.4 cycloocta- 1,5-diene, 152 10 and cycloocta-l,3,5,7-tetraene, 2.60 0.19 the indicated errors are two least-squares standard deviations and do not include the uncertainties in the rate constants for the reference alkenes (propene, but-l-ene, d.s-but-2-ene, trans-but-2-ene, 2-methylbut-2-ene, and terpinolene). These rate data were compared with the few available literature data, and the effects of methyl substitution have been discussed.50... 

Gas-phase ozonolyses of ethene, cis- and trans-but-2-ene, isoprene, as well as several monoterpenes such as o-pinene, /3-pinene, 3-carene, limonene, and /3-myrcene have been performed by trapping the reaction products in C>2-doped argon matrices and recording the IR spectra <2000SAA2605>. Bands characteristic for the secondary ozonides were identified after bleaching by broad-band UV-Vis photolysis. In the case of isoprene 34, a secondary ozonide appears to be formed more likely at the more substituted double bond however, the two possible carbonyl compounds 35 and 36 could not be put into evidence by infrared (IR) in the reaction condensate as these reacted further with O3 (Scheme 6). 

C4H6)t But-l-ene, cls-but-2-ene, trans-but-2-ene, 2-methyl propene, methyl cyclopropane, cyclobutane 15 g, 1 427... 

Fig. 3.5. Relationship between log (retention time) and boiling point for a range of hydrocarbons on squalane at 43°C. A, aliphatics (and benzene) B, alicyclics, 1-4 = C5-Cg n-alkanes 5 = 2-methyl-butane 6 = 2-methylpentane 7 = 2,3-dimethylbutane 8-12 = C4-C8 1-olefins 13,15,17 = trans-(but-2-ene, pent-2-ene and hept-2-ene) 14,16,18 = e/s-(but-2-ene, pent-2-ene and hept-2-ene) 19 = 2-methylbut-l-ene 20 = 2-methylpent-l-ene 21 = 4-methylpent-l-ene 22 = 2-methylbut-2-ene 23 = cyclopentane 24 = cyclohexane 25 = methylcyclopentane 26 = methylcyclohexane 27 = cyclo-pentene 28 = cyclohexene 29 = 4-methylcyclohexane 30 = 1,3-butadiene 31, 32 = trans- and cis-1,3-pentadiene 33 = diallyl 34, 35 = trans- and c s-2-methyl-l,3-pentadiene 36 = cyclopentadiene ...

The molecule with the methyl groups on the same side of the double bond is called ri.y-bul-2-cnc, and the one with the methyl groups on opposite sides is called trans-but-2-ene. These kinds of molecules are discussed further in Section 2-8B. 

Stereoisomers are isomers that differ only in how their atoms are oriented in space. Their atoms are bonded in the same order, however. For example, cis- and trans-but-2-ene have the same connections of bonds, so they are not constitutional isomers. They are stereoisomers because they differ only in the spatial orientation of the groups attached to the double bond. The cis isomer has the two methyl groups on the same side of the double bond, and the trans isomer has them on opposite sides. In contrast, but-l-ene is a constitutional isomer of cis- and fran.v-but-2-ene. 

Relative heats of hydrogenation. trans-But-2-ene is more stable than but-l-ene by 11 kJ/mol (2.7 kcal/mol). 

Rotating meso-2,3-dibromobutane into a conformation where the bromine atoms are anti and coplanar, we find that the product will be trans-but-2-ene. A similar conformation of either enantiomer of the ( ) diastereomer shows that the product will be cw-but-2-ene. Hint Your models will be helpful.)... 

Show how you would accomplish each of the following synthetic conversions, (a) trans-but-2-ene --- fra 5-l,2-dimethylcyclopropane... 

---