Question

Which of the following is the most stable alkene?
(a) \[{R_2}C = C{R_2}\]
(b) \[RCH = CHR\]
(c) \[RC{H_2} = C{H_2}R\]
(d) \[{H_2}C = C{H_2}\]

Answer 1

Hint: The stability of alkene varies with different conditions. To explore the stability of alkene in the given question we must look at the substituents and on the conjugated double bonds. An alkene with a conjugated double bond is considered more stable compared to a non-conjugative alkene.

Complete Step by Step Answer:
In chemistry, we all know that alkene is an unsaturated hydrocarbon composed of carbon and hydrogen. Alkene can also be categorised into symmetrical and unsymmetrical on the bases of the position of double bonds.

The stability of alkene can be defined in the terms of conjugation and on the basis of the alkyl group attached to it.

Alkene with a conjugative double bond is considered more stable than unconjugated alkene due to the delocalization of the double bond. This delocalization of the double bond in conjugated alkenes causes lower in energy therefore the conjugated alkenes are more stable.

Whereas alkenes which have a greater number of the alkyl group or electron releasing group are also considered more stable alkene (due to the +R effect) than alkene that has a smaller number of alkyl substituents. In studies, it was also found that cis alkenes are more stable than the trans-alkenes.

Now in the question see the given option (a) showing the most substituted alkene. Whereas options (b) and (d) represent monosubstituted and unsubstituted alkene respectively. However, option (c) is representing the wrong structure of an alkene. Hence the stability of alkene can be represented as based on substituents.
\[{R_2}C = C{R_2} > RCH = CHR > {H_2}C = C{H_2}\]
Therefore, from the above discussion, it is quite clear that \[{R_2}C = C{R_2}\]will be the more stable alkene. Hence option (a) will be the correct answer.

Note: Alkenes are insoluble in water due to their non-polar nature. Alkenes are considered more reactive than alkanes. The cis-isomer of alkene possesses a lower melting point than the trans-isomer.