Rings containing sp2 hybridized carbon atoms cyclohexanone and cyclohexene

Rings containing sp hybridized carbon atoms cyclohexanone and cyclohexene 

Six-membered rings with more than one sp2 C atom do lose their chair conformation—they become flattened to some degree when there are one or more double bonds included in the ring. Cyclohexene, with just one double bond in the ring, has a half-chair conformation similar to that of its related epoxide, cyclohexene oxide. The usual conformational diagram of cyclohexene is shown below. The barrier for ring inversion of cyclohexene is around 22 kj mol-1 (about half that for cyclohexane ). 

Make sure you pointthe ketone in the right direction It should bisect the angle there would be between the axial and equatorial substituents, if the carbon atom were tetrahedral. It s always best to put the carbonly group atone of the end carbons of the ring it s much harder to get it right if you join it to one of the middle ones. 

We will look more closely at the reactions of cyclohexene along with other alkenes in later chapters. For now, we return to the chemistry of cyclohexanones. Before you had read this chapter you might simply have drawn the mechanism for nucleophilic attack on cyclohexanone as shown. 

The product contains the two functional groups Nu and OH, which you now know can be arranged in two conformations one in which the alcohol is axial and one in which it is equatorial. But we can t predict which conformation is more favourable without knowing what the group Nu is if Nu is smaller than 

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