Question

An unknown compound C of molecular formula C₆H₁₂O₃ exhibits a strong absorption in its IR spectrum at 1718 cm^-1 and the given ¹H NMR spectrum. What is the structure of C?

Short answer

Spectral data is used to identify unknown compounds.

Each atom or group present in a compound shows a characteristic absorption that is represented as a spectrum and hence the spectrum obtained for a compound can be used to predict its structure.

Step-by-step solution

Spectral data

Spectral data is used to identify unknown compounds.

Each atom or group present in a compound shows a characteristic absorption that is represented as a spectrum and hence the spectrum obtained for a compound can be used to predict its structure.

Inference from the IR data

The molecular formula of the compound is C₆H₁₂O₃ and the compound shows an IR absorption at 1718 cm^-1.

IR absorption at 1718 cm^-1 is characteristic of carbonyl (C=O) stretching and therefore, the compound consists of a carbonyl group.

Inference from the 1H-NMR spectrum

The singlet at 2.2 ppm corresponding to three hydrogens indicates that the carbon adjacent to the one to which the concerned proton contains two hydrogen atoms.

(According to the n+1 rule, where n indicates the number of hydrogen atoms on the adjacent carbon).

Doublet at 2.7 corresponding to 2H (number of adjacent hydrogen atoms is 1).

The singlet at 3.2 corresponds to 6H (carbon adjacent to six equivalent hydrogens is not connected to a proton).

Triplet at 4.8 corresponds to 1H (adjacent carbon contains two protons).

Therefore, the predicted structure of compound C is:

Structure of compound C