A compound gives a mass spectrum with essentially only three peaks at m/z = 77 (40%), 112 (100%), and 114 (33%). Identify the compound

It is defined as the technique to identify the molecular structure of the compound by the charge to mass ratio of the possible peaks produced from which we can determine the possible molecular formula.

This method involves the ionization of the compound and we can identify the structure mainly on the basis of two types of peaks one is intense peaks and another is molecular ion peak.

As the three molecular ion peaks are three 77,112,144 and the M+2 peak is 144 and the M molecular ion peak is 112 therefore the abundance of M+2 is the 30% of M so the compound must contain chlorine atom and the mass to charge ratio at 77 is due to the loss of chlorine ion (112-35=77).

It does not show further fragmentation so it must be a phenyl chain so the compound must be chlorobenzene as shown below: