91Ó°ÊÓ

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

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

Functional group absorption band

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.

Here four absorption bands will be seen:

• Nitro group absorption band is seen at 1540 \(c{m^{ - 1}}\).
• Aldehyde group absorption band is at 1730 \(c{m^{ - 1}}\).
• Aromatic ring \( - C = C - \) band at1450-1600 \(c{m^{ - 1}}\).
• Aromatic ring \(C - H\) band at3030 \(c{m^{ - 1}}\).

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

Here three absorption bands will be seen:

• Ester group absorption band is seen at 1735 \(c{m^{ - 1}}\).
• Alkene \( - C = C - \) band at1640-1680 \(c{m^{ - 1}}\).
• Alkene \( = C - H\) band at3020-3100 \(c{m^{ - 1}}\).

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

Here four absorption bands will be seen:

• Ketone group absorption band is seen at 1715 \(c{m^{ - 1}}\).
• Alcohol group absorption band is at 3400-3650 \(c{m^{ - 1}}\).