Q35E
Question
Ring-opening of the trans-cyclobutene isomer shown takes place at much lower temperature than a similar ring-opening of the cis-cyclobutene isomer. Explain the temperature effect, and identify the stereochemistry of each reaction as either conrotatory or disrotatory.
Step-by-Step Solution
VerifiedThe ring-opening of the cis-cyclobutene takes place in disrotatory manner and ring opening of trans-cyclobutene takes place in a conrotatory manner. According to Stereochemical Rules for Electrocyclic Reaction,conrotatary is favored for the reactions involving an even number of electron pairs in thermal conditions hence and ring-opening of trans-cyclobutene takes place at a lower temperature.
The ring-opening of the cis-cyclobutene takes place in disrotatory manner as u can see from the following mechanism:
In this case, only disrotatory path is possible, as the alternative path would result in a highly strained trans-double bond within a cyclohexene ring.
The ring-opening of the trans-cyclobutene takes place in a conrotatory manner as u can see from the following mechanism:
Conrotatary is favoured for the reactions involving even number of elevtron pairs in thermal conditions hence it takes place at lower tempreature.