The ultimate test of fluency in MS and IR is whether you can determine a moderately complex structure from just the MS and the IR, with no additional information. The IR and MS of a compound are shown below. Use everything you know about IR and MS, plus reasoning and intuition, to determine a likely structure. Then show how your proposed structure is consistent with these spectra.

In the given mass spectrum of the compound:

M+ =121(odd)

as M+ peak is odd, that is, 121 and fragment even at 106. So, Nitrogen may be present in the compound.

In IR spectrum of the compound, there is peak at 3400cm^-1 broad and sharp spike which indicates a peak of N-H and peak at 1620cm^-1. This indicates amide group may be present in the compound.

In mass spectrum of a compound, M/z peak is present at 77 which indicates that phenyl ring is present in the compound.

Molecular ion peak=121

Amide group is present (-CONH₂)

Mass of amide group=12+16+14+2=44

After removing mass of an amide functional group, 121-14=77

From rule of 13 C_nH_n

M/13= n+ remainder

77/13= 5+ 12 remainder

n=5

The molecular mass of carbon is 12.

Molecular formula is C₅H₅+C+CONH₂

Molecular formula= C₆H₅CONH₂

From the above conclusion, most probable structure of the compound is:

Benzamide