Question

The organic compound 1,4-dimethylbenzene (also known as p-xylene) has the formula $\mathbf{\left(}\mathbf{CH}\mathbf{3}\mathbf{\right)}\mathbf{2}\mathbf{C}\mathbf{6}\mathbf{H}\mathbf{4}$ . Its structure hastwo$\mathbf{CH}\mathbf{3}$ (methyl) groups substituted at opposite positions on thebenzene$\left(\mathbf{C}\mathbf{6}\mathbf{H}\mathbf{6}\right)$ ring. Predict the number of peaks in the low-resolution proton NMR spectrum of this compound and the relative areas of the peaks.

Short answer

The Number of peaks is 2 and the relative peak area is 2:3

Step-by-step solution

Homotopic Proton definition 

The word "homotopy" simply means "identical." All of the protons in ethane, for example, are homotopic. Despite the fact that each proton is physically distinct, we refer to them as identical because the rotation around the C-C single bond is so quick that all protons seem in the same environment on average.

Chemically, homotopic protons are the same and produce the same signal.

Diastereotopic Proton definition

Diastereotopic protons are chemically non-equivalent, so give different signal.

Predicting the number of peaks 

We have structure of 1,4-dimethylbenzene

In this there are two types of protons present –$CH$(a) and –$CH3$(b), which are chemically non-equivalent, so they will give two signals, so the number of peaks is2.

We have (a)type protons are 4 and (b) type protons are 6, so the relative peak area would be 4:6 which would become 2:3.

So, the Number of peaks is 2 and the relative peak area is 2:3.