Question

A compound was isolated as a minor constituent in an extract from garden cress. Its spectra are shown here.

1. Look at each spectrum individually and list the structural characteristics you can determine from that spectrum.
2. Look at the set of spectra as a group and propose a tentative structure.
3. Verify that your proposed structure accounts for the major features of each spectrum.

Short answer

1. IR spectrum: From the given IR spectrum, it is deduced that, noorpeak appears. Hydrogens bonded to bothandcarbon are indicated around 3000The characteristicpeak appears at 2250and aromaticis suggested by the peak at 1600.

Mass spectrum: The molecular ion of m/z 117 suggests the presence of an odd number of nitrogens.

NMR spectrum: From NMR data, five aromatic protons are shown in chemical shift value 7.3 and a singlet appears at chemical shift value 3.7.

2. The proposed structure deduced from the given spectra data is,

3. Assembling the information from given spectrum data, that is from IR, NMR and mass spectrum, we have following fragments,

The proposed structure deduced from the given spectrum data will be, 2-phenylacetonitrile.

Step-by-step solution

IR spectrum data:

From the given IR spectrum, it is deduced that, noorpeak appears. Hydrogens bonded to bothandcarbon are indicated around 3000. The characteristicpeak appears at 2250and aromaticis suggested by the peak at 1600.

Structure elucidation from given mass and NMR data:

In mass spectrum, the vertical axis denotes the relative abundance of ions. The most intensive peak in a spectrum is called as base peak. In the mass spectrum, the relative intensity of each ion is normally found using the peak with the highest intensity as standard or base peak. The heaviest ion or the one with greatest m/z value is the molecular ion.

The molecular ion of m/z 117 suggests the presence of an odd number of nitrogens.From NMR data, five aromatic protons are shown in chemical shift value 7.3 and a singlet appears at chemical shift value 3.7.

Assembling the fragments we have,

The proposed structure deduced from the given spectrum data will be, 2-phenylacetonitrile.

Proposed structure from given spectrum data