Butene trans

The goal of this project is to determine the enthalpies of formation of cis- and trans-2-butene and to calculate the enthalpy of isomerization between them. 

In stereoselective antitheses of chiral open-chain molecules transformations into cyclic precursors should be tried. The erythro-configurated acetylenic alcohol given below, for example, is disconnected into an acetylene monoanion and a symmetrical oxirane (M. A. Adams, 1979). Since nucleophilic substitution occurs with inversion of configuration this oxirane must be trens-conilgurated its precursor is commercially available trans-2-butene. 

The pair of isomers designated as and trans 2 butene have the same constitution both have an unbranched carbon chain with a double bond connecting C 2 and C 3 They differ from each other however m that the cis isomer has both of its methyl groups on the same side of the double bond but the methyl groups m the trans isomer are on oppo site sides of the double bond Recall from Section 3 11 that isomers that have the same constitution but differ m the arrangement of their atoms m space are classified as stereoisomers as 2 Butene and trans 2 butene are stereoisomers and the terms as and trans specify the configuration of the double bond... 

FIGURE 5 2 Interconversion of as and trans 2 butene proceeds by cleavage of the tt component of the double bond The yellow balls represent methyl groups... 

In principle cis 2 butene and trans 2 butene may be mterconverted by rotation about the C 2=C 3 double bond However unlike rotation about the C 2—C 3 single bond in butane which is quite fast mterconversion of the stereoisomeric 2 butenes does not occur under normal circumstances It is sometimes said that rotation about a carbon-carbon double bond is restricted but this is an understatement Conventional lab oratory sources of heat do not provide enough energy for rotation about the double bond m alkenes As shown m Figure 5 2 rotation about a double bond requires the p orbitals of C 2 and C 3 to be twisted from their stable parallel alignment—m effect the tt com ponent of the double bond must be broken at the transition state... 

Alkenes resemble alkanes m most of their physical properties The lower molecular weight alkenes through 4 are gases at room temperature and atmospheric pressure The dipole moments of most alkenes are quite small Among the 4 isomers 1 butene cis 2 butene and 2 methylpropene have dipole moments m the 0 3-05 D range trans 2 butene has no dipole moment Nevertheless we can learn some things about alkenes by looking at the effect of substituents on dipole moments... 

FIGURE 5 5 Ball and spoke and space filling models of as and trans 2 butene The space filling model shows the serious van der Waals strain between two of the hydrogens in as 2 butene The molecule ad justs by expanding those bond angles that increase the separation between the crowded atoms The combi nation of angle strain and van der Waals strain makes as 2 butene less stable than trans 2 butene... 

Hydnde shifts often occur during the dehydration of primary alcohols Thus although 1 butene would be expected to be the only alkene formed on dehydration of 1 butanol It IS m fact only a minor product The major product is a mixture of cis and trans 2 butene... 

Whatever happens at one enantiotopic face of the double bond of as or trans 2 butene hap pens at the same rate at the other resultrng mail mrxture of R) and (S) 2 bromobutane... 

The syn stereochemistry of dibromocarbene cycloaddition was demonstrated in experiments using as- and trans-2 butene Give the structure of the product obtained from addition of dibromocarbene to each alkene... 

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... 

Which alkene c/s-2 butene or trans-2 butene would you... 

Epoxidation of cis 2 butene gives meso 2 3 epoxybutane trans 2 butene gives a racemic mixture of (2R 3R) and (2S 3S) 2 3 epoxybutane... 

ALCOHOLS,HIGHERALIPHATIC - SYNTHETIC PROCESSES] rVol 1) trans-2-Butene [110-57-6]... 

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