Hexamethylbenzene undergoes radical bromination with N-bromosuccinimide to give one monobrominated productand four dibrominated products. These products are easily separated by GC-MS, but the dibrominated products are difficult to distinguish by their mass spectra. Draw the monobrominated product and the four dibrominated products and explain howNMR would easily distinguish among these compounds.

Hexamethylbenzene on reaction with N-bromosuccinimide undergoes radical bromination reaction and gives one monobrominated and four dibrominated products. Allylic bromination reaction takes place in which allylic hydrogen gets substituted with the bromine group. On substitution of one hydrogen of methyl group, monobrominated product forms and on substitution of two hydrogens of methyl group, dibrominated product forms. Also, one hydrogen of one methyl group and other hydrogen of second methyl group can get substituted and dibrominated product can form.

Symmetry and chemical shift values of the methyl groups in the carbon-NMR can distinguish the five compounds which are obtained by allylic bromination of hexamethylbenzene. In monobrominated compound, four types of peaks are there and one short peak at chemical shift value 45. Differentiation between dibrominated compounds is also done by number of peaks and chemical shift values as shown in the structures below. Higher value of chemical shift is due to presence of two chlorine atoms as more electronegative atoms increases the value of chemical shift of adjacent carbon by making it more electron deficient and lesser the electron density available on the carbon, more will be its chemical shift value.