Question

Question: Where might the following compound have IR absorptions?

Short answer

Absorption bands seen at 2210-2260${\mathrm{cm}}^{-1}$ , 1690${\mathrm{cm}}^{-1}$ and 1640-1680${\mathrm{cm}}^{-1}$ .

Step-by-step solution

Absorption spectrum

The absorption spectrum has dark lines in the spectrum when radiation is transmitted through a substance, indicating absorption at specific wavelengths of electromagnetic radiation.

Chart for absorption by specific functional group

The given chart has values for absorption of particular wavelength radiation by specific functional group.

Functional groups present in (a) compound

Here three functional groups are present namely aromatic ring, nitro group and aldehyde group. Red atom indicated here is oxygen and the blue atom is nitrogen according to book convention.

Absorption bands for the spectrum of (a)

Here four absorption bands will be seen:

• Nitro group absorption band is seen at 1540${\mathrm{cm}}^{-1}$ .

• Aldehyde group absorption band is at 1730${\mathrm{cm}}^{-1}$ .

• Aromatic ring $-\mathrm{C}=\mathrm{C}-$ band at 1450-1600${\mathrm{cm}}^{-1}$ .

• Aromatic ring $\mathrm{C}-\mathrm{H}$ band at 3030${\mathrm{cm}}^{-1}$ .

Functional groups present in (b) compound

Here two functional groups are present namely ester and alkene group. Red atom indicated here is oxygen.

Absorption bands for a spectrum of (b)

Here three absorption bands will be seen:

• Ester group absorption band is seen at 1735${\mathrm{cm}}^{-1}$ .

• Alkene $-\mathrm{C}=\mathrm{C}-$ band at 1640-1680 ${\mathrm{cm}}^{-1}$.

• Alkene $=\mathrm{C}-\mathrm{H}$band at 3020-3100 ${\mathrm{cm}}^{-1}$.

Functional groups present in (c) compound

Here two functional groups are present namely the ketone and alcohol groups. The red atom indicated here is oxygen.

Absorption bands for the spectrum of (c)

Here four absorption bands will be seen:

• Ketone group absorption band is seen at 1715${\mathrm{cm}}^{-1}$ .

• Alcohol group absorption band is at 3400-3650 ${\mathrm{cm}}^{-1}$.