JEE Main · 2023 · 31 Jan 2023 · Shift 2 · Hydrocarbons

The formula ${\mathrm{C}}_6{\mathrm{H}}_8$ carries four degrees of unsaturation, and since only two moles of hydrogen are taken up on hydrogenation, two of these are carbon-carbon double bonds within a ring. Ozonolysis giving two moles of the same dialdehyde, $\mathrm{OHC}\text{-}\mathrm{C}{\mathrm{H}}_2\text{-}\mathrm{CHO}$ (malonaldehyde, that is methanedicarbaldehyde), requires each double bond to be flanked by a single $\mathrm{C}{\mathrm{H}}_2$ on the way to the next. Cleaving the two double bonds of cyclohexa-1,4-diene breaks the ring into two identical $\mathrm{OHC}\text{-}\mathrm{C}{\mathrm{H}}_2\text{-}\mathrm{CHO}$ fragments. The hydrocarbon X is cyclohexa-1,4-diene.