Q12P - Organic Chemistry (Mcmurry)

Question

Where might the following compound have IR absorptions?

Step-by-Step Solution

Answer

Absorption bands seen at 2210-2260 cm^-1 , 1690 cm^-1 and 1640-1680 cm^-1 .

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 bookconvention. 

Absorption bands forthe spectrum of (a)

Here four absorption bands will be seen:

• Nitro group absorption band is seen at 1540 cm^-1.
• Aldehyde group absorption band is at 1730 cm^-1  . 
• Aromatic ring -C = C - band at 1450-1600 cm^-1  .
• Aromatic ring C- H  band at3030 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 cm^-1 .
• Alkene -C = C - band at 1640-1680 cm^-1   .
• Alkene = C- H band at3020-3100 cm^-1 .

Functional groups present in (c) compound

Here two functional groups are present namely the ketone and alcoholgroups. 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 cm^-1 .
• Alcohol group absorption band is at 3400-3650 cm^-1  .