Question

An unknown compound D exhibits a strong absorption in its IR spectrum at 1692 cm^-1 . The mass spectrum of D shows a molecular ion at m/z = 150 and a base peak at 121. The ¹H- NMR spectrum of D is shown below. What is the structure of D?

Short answer

Spectroscopy is used to study the structure of compounds and can be used to predict or identify unknown compounds.

Step-by-step solution

Spectroscopy

Spectroscopy is used to study the structure of compounds and can be used to predict or identify unknown compounds.

Mass spectrum of the given compound

The m/z value of molecular ion in mass spectrum gives the molecular mass of the compound.

The molecular mass of the compound is 150.

Therefore, the possible molecular formula of the compound is C₉H₁₀O₂ .

Analyzing the IR and   1H-NMR spectrum of the given compound

The IR spectrum shows a strong absorption peak at 1692 cm^-1 is characteristic of the carbonyl (C=O) group.

The NMR data:

Triplet at 1.5 corresponding to three hydrogen atoms indicates the carbon atom adjacent to the one bonded to the desired hydrogen contains two hydrogen atoms (-CH₃CH₂-) .

Quartet corresponding to three hydrogens at 4.1 ppm represents theCH₂ group adjacent to a CH₃ group.

Doublet at 7.0 ppm (2H) corresponds to two aromatic protons.

Doublet at 7.8 ppm (2H) corresponds to two aromatic protons.

(Since two peaks in the aromatic region correspond to two hydrogen atoms, each indicates that the benzene ring is para-substituted).

The singlet at 9.9 corresponds to the aldehydic proton.

Therefore, the structure of compound D is:

Structure of compound D