Cyclooctene: trans

Cycloalkenes that have trans double bonds m rings smaller than 12 mem bers are less stable than their cis stereoisomers trans Cyclooctene can be isolated and stored at room temperature but trans cycloheptene is not stable above -30°C... 

Calculate energy differences between cis and trans-cycloheptene and cis and trans-cyclooctene. Which is the more stable isomer for each compound Is there a significant (>.008 au or 5 kcal/mol) increase in the energy difference between cis and trans isomers in going from the seven to eight-membered cycloalkene Are your results consistent with the fact that trans-cyclooctene is an isolable, stable compound while trans-cycloheptene is not ... 

Compare geometries of the cis and trans cycloalkenes. Are the double bonds incorporated into the trans compounds significantly more distorted than those incorporated into the analogous cis cycloalkenes Consider carbon-carbon bond lengths and the twisting and/ or puckering of the double bond. Are any distortions greater in trans-cycloheptene than in trans-cyclooctene ... 

Another measure of distortion is the shape of the highest-occupied molecular orbital (HOMO). This corresponds to the 7t bond. Is the orbital relatively undistorted in the cis compounds (as in cis-2-butene)l Is it more distorted in trans-cycloheptene than in trans-cyclooctene Explain why distortion in the HOMO is likely to be energetically unfavorable. 

As previously mentioned, double bonds in relatively small rings must be cis. A stable trans double bond first appears in an eight-membered ring trans-cyclooctene, p. 134), though the transient existence of tran -cyclohexene and cycloheptene has been demonstrated. Above 11 members, the trans isomer is more stable than the cis. It has proved possible to prepare compounds in which a trans double bond is shared by two cycloalkene rings (e.g., 104). Such compounds have been called [m.n]betweenanenes, and several have been prepared with m and n values from 8 to 26. The double bonds of the smaller betweenanenes, as might be... 

Figure 4. IR spectra in D -doped liquid Kr at -120°C of (OC) Cr(ol) and of the photolysis product (OC) Cr(ol)(D ) [ol = trans-cyclooctene]. D2 was used rather than H2 to avoid potential spectral overlap of any V(H-H) bands with bands due to the hydrocarbon ligand.

Fig. 12. trans-Cyclooctene a calculated (19) and observed (78) (in parentheses) torsion angles (deg) of the crown conformation b calculated torsion angles of the distorted chair conformation... 

However, given a sufficiently strong steric effect, a permanent twist can be induced in a carbon-carbon double bond even without a push-pull effect. This is a field that has been the subject of much interest, as exemplified by the intense but still unsuccessful search for tetra-/m-butylethylene, and by the still very active studies of trans-cyclooctenes. Besides the synthetic challenge, such compounds present interesting chiroptical and other physical properties, and a knowledge of their heats of formation presents crucial tests for current force fields. 

C. trans-Cyclooctene. A 500-ml., three-necked, round-bottomed flask is equipped with a nitrogen inlet capillary tube (Note 9), a short (10-20 cm.) unpacked column (Note 10), and a pressure-equalizing dropping funnel. The round-bottomed flask is connected by the unpacked column to a 100-ml. trap cooled in an ice bath. This trap is then connected to a 200-ml. trap cooled in dry ice-acetone (Note 11). The flask is heated in an oil bath to 110-125°, and the apparatus is evacuated to a pressure of ca. 10 mm. under a constant sweep of nitrogen. The hydroxide solution is added dropwise at approximately the rate of decomposition of the quaternary ammonium hydroxide (Note 12). 

Ebenso ist seit langem trans-Cycloocten als relativ stabile, isolier-bare Verbindung bekannt (70). 

Other tris(olefin)platinum(0) complexes (where olefin represents a strained olefin such as bicyclo[2.2.1]heptene, dicyclopentadiene, or trans-cyclooctene) may be similarly obtained by direct displacement of 1,5-cyclooctadiene, often in quantitative yield.6... 

Addition of formic acid to cts- and trans- cyclooctene oxkk-hae been studied with admirable precision by Cope and bis students,838-s 0-342-514 SJ7> 848 with the help of modem vapor phast chromatographic technique. Hydrolysis of the crude mixture of mono-fbrmate esters obtained from cM-oydoaotene oxide gave a coniph- mixture of no lees than ten components, eight of which have already been identified (Eq. 709)-... 

Vic-diols can thus be easily converted to alkenes through their reaction with A, A -thiocarbonyldimidazule. The reported synthesis of trans-cyclooctene is illustrative of the method [219]. It should be noted that continuous elimination of rrans-cyclooctene by a stream of argon was necessary to avoid isomerization to the cis isomer. The conversion of cis-cyclooctene to ww-cyclooctene through a trithiocarbonate is described in the same paper. 

One of the most interesting developments in the stereochemistry of organic compounds in recent years has been the demonstration that trans-cyclooctene (but not the cis isomer) can be resolved into stable chiral isomers (enantiomers, Section 5-IB). In general, a Wa/w-cycloalkene would not be expected to be resolvable because of the possibility for formation of achiral conformations with a plane of symmetry. Any conformation with all of the carbons in a plane is such an achiral conformation (Figure 12-20a). However, when the chain connecting the ends of the double bond is short, as in trans-cyclooctene, steric hindrance and steric strain prevent easy formation of planar conformations, and both mirror-image forms (Figure 12-20b) are stable and thus resolvable. 

This subject has recently been reviewed.647 Several additional papers have appeared on the catalytic oxidation of alkenes by 02 in the presence of PdCl(MeCN)2N02(148).64S Terminal alkenes and trans- cyclooctene yield the corresponding ketones, cyclopentene and cyclohexene the corresponding allyl alcohol, and bicyclic alkenes the corresponding epoxide. Heterometallacy-clopentanes such as (152) have been isolated from the reaction of (148) with norbornene (dicy-clopentadiene), and characterized by X-ray crystallography.6486 Glycol monoacetates were obtained from the reaction of (148) with terminal alkenes in acetic acid.649... 

Base removes bepzylic H, retro- allyl anion+alkene, all-s gives trans-cyclooctene retro [2+2], s on both a-bonds makes trani-double bond. This is an exercise in drawing believable transition structures like 6.42. 

Several factors influence product formation in triazoline thermolysis. The stereochemistry of the triazoline adducts from cis- and trans-cyclooctene has been found to play a role in aziridine or imine formation aziridines predominate in the trans and imines in the cis isomers.86 However, the relative product ratios depend on the reaction temperature, and thermolysis of the cis-triazoline at 310°C leads to 78% aziridine as against 5% at 80°C.87... 

This review will start with trans -cyclooctene for reasons that will become clear later. 

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