Trans-Pent-2-ene

Comparison of the results for catalytic isomerization of pent-l-ene to trans-pent-2-ene with the basic and one-electron donating properties of the catalysts led to the conclusion that two different reaction mechanisms operate in double bond isomerization reactions (a) an ionic mechanism which involves proton abstraction from the alkene molecule by the super base site (pAia = 37 for pentenes) and (b) a free radical mechanism which involves the abstraction of a hydrogen atom from the alkene by the one-electron donor center (Scheme 39). 

There are many instances of the isomerisation of alkenes or alkenilic compounds under the influence of transition metal compound catalyst. Some examples arepent-l-ene into cis- and trans-pent-2-ene (RhCl3... 

In Chapter 7, we used heats of hydrogenation to compare the relative stabilities of alkenes. For example, the heats of hydrogenation of pent-l-ene and fran.s-pent-2-ene show that the disubstituted double bond in trans-pent-2-ene is 10 kJ/mol (2.5 kcal/mol) more stable than the monosubstituted double bond in pent-l-ene. 

The specific degradation of epoxides of cis- and trans-pent-2-enes is discussed in Chapter 6, Section 6.1.3. 

Scheme 6.2 Possible structures of puckered metallacycle intermediates in the productive metathesis reactions of trans-pent-2-ene.

In the case of 41 (experimental conditions 41 —100 torr, oxygen—10 torr, H2—2 mCi, volume of the pyrex vessel 500 ml, storage period 250-263 days, temperature 90 °C), besides tritiated 41 (6.2%), tritiated methane (15.2%), ethene (1.9%), propene (14.2%), cis-but-2-ene (2.3%) and 2-methylbut-2-ene + trans-pent-2-ene (8.1%) have been isolated. In the case of reaction of with bicyclo[2.1.0]pentane (42), the yields of the tritiated... 

The two Schrock carbenes (complexes 2 and 3) are not stereoselective With trans-pent-2-ene the resulting olefin always has the thermodynamic cis/trans ratio while with a>pent-2-ene there is formation, at the beginning of the reaction, of cis and trans olefins in quite the same amounts. 

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