Thermal Ring Opening Reactions of Cyclo Butane

Introduction:
Cyclo butane is a cyclic alkane with four carbon atoms in a ring. It is known for its high ring strain due to its puckered structure. When cyclo butane undergoes a thermal ring opening reaction, the mechanism can either be conrotatory or disrotatory.

Conrotatory Mechanism:
In the conrotatory mechanism, the breaking of the sigma bonds in the ring occurs in a synchronous manner. This means that the two carbon-carbon sigma bonds on either side of the ring break at the same time, and the two resulting electrons move in the same direction. This leads to the formation of a planar intermediate with a pi bond. The pi bond then rotates, and the two carbon atoms on either side of the ring come closer together to form a new sigma bond. This results in the formation of an open-chain alkene.

Disrotatory Mechanism:
In the disrotatory mechanism, the breaking of the sigma bonds in the ring occurs in an asynchronous manner. This means that the two carbon-carbon sigma bonds on either side of the ring break at different times, and the two resulting electrons move in opposite directions. This leads to the formation of a twisted intermediate with two pi bonds. The pi bonds then rotate, and the two carbon atoms on either side of the ring move further apart to form two new sigma bonds. This results in the formation of an open-chain diene.

Temperature Dependence:
The mechanism of the thermal ring opening reaction of cyclo butane depends on the temperature at which the reaction is carried out. At high temperatures, the reaction is conrotatory, while at low temperatures, the reaction is disrotatory. This is due to the fact that the activation energy for the conrotatory mechanism is lower at high temperatures, while the activation energy for the disrotatory mechanism is lower at low temperatures.

Conclusion:
In conclusion, the thermal ring opening reaction of cyclo butane can occur via either a conrotatory or disrotatory mechanism, depending on the temperature at which the reaction is carried out. At high temperatures, the reaction is conrotatory, while at low temperatures, the reaction is disrotatory.