A laboratory student was converting cyclohexanol to cyclohexyl bromide by using one equivalent of sodium bromide in a large excess of concentrated sulfuric acid. The major product she recovered was not cyclohexyl bromide, but a compound of formula C₆H₁₀that gave the following ¹³CNMR spectrum:

1. Propose a structure for this product.
2. Assign the peaks in the ¹³CNMR spectrum to the carbon atoms in the structure.
3. Suggest modifications in the reaction to obtain a better yield of cyclohexyl bromide.

Molecular formula C₆H₁₀indicates two degrees of unsaturation which means, that either two double bonds or a triple bond or one double bond and one ring is present. From the given spectrum, it is observed that, peak at chemical shift value 125 occurs and it indicates an aromatic system with a double bond and directs towards cyclohexene. The structure is further confirmed by the peak which occurs at chemical shift values 23 and 25 which signifies methylene groups, thus a ring must be present with double bond in it.

Cyclohexene

From the given spectrum, the peak at chemical shift value 125 indicates the presence of an aromatic system with a double bond, and chemical shift values 23 and 25 indicate the presence of methylene groups in the system, which further establishes the structure cyclohexene with these chemical shift values.

a = δ 128, b = δ 25, c = δ23

Chemical shift values for cyclohexene system

To obtain a better yield of cyclohexyl bromide, using PBr₃ instead of sulphuric acid or sodium bromide can prove beneficial as the conversion rate for the reaction of cyclohexanol to cyclohexyl bromide is more and it is also less harmful and produce less waste in the reaction mixture.