Question

Examine the IR spectrum of aspirin. Several significant signals have been identified on the spectrum. Assign these signals to corresponding functional groups in the molecule of aspirin. Explain your rationale clearly.

Answer 1

Concepts and reason

The concept used here to solve the problem is based on the infrared spectroscopy. Based on the values ${\rm{IR}}$ absorption the functional groups are identified in the aspirin.

Fundamentals

The general table of characteristic ${\rm{IR}}$ absorption of certain functional groups is as follows.

The structure of aspirin is shown below.

In the structure of aspirin, the functional groups and their signals are as follows.

Carboxylic group ${\rm{COOH}}$

${\rm{(C = O)}}$ stretching ${\rm{1725 c}}{{\rm{m}}^{ - {\rm{1}}}}$

${\rm{(O}} - {\rm{H)}}$ stretching $3400{\rm{ c}}{{\rm{m}}^{ - {\rm{1}}}}$

Ester ${\rm{OCOC}}{{\rm{H}}_{\rm{3}}}$

${\rm{(C = O)}}$ stretching $1740{\rm{ c}}{{\rm{m}}^{ - 1}}$

Aromatic group (benzene)

${\rm{(C}} - {\rm{H)}}$ stretching $3030{\rm{ c}}{{\rm{m}}^{ - 1}}$

${\rm{(C = C)}}$ stretching $1600{\rm{ c}}{{\rm{m}}^{ - 1}}$

Ans:

In the structure of aspirin, the functional groups and their signals are as follows.

Carboxylic group ${\bf{COOH}}$

${\bf{(C = O)}}$ stretching ${\bf{1725 c}}{{\bf{m}}^{{\bf{ - 1}}}}$

${\bf{(O - H)}}$ stretching ${\bf{3400 c}}{{\bf{m}}^{{\bf{ - 1}}}}$

Ester ${\bf{OCOC}}{{\bf{H}}_{\bf{3}}}$

${\bf{(C = O)}}$ stretching ${\bf{1740 c}}{{\bf{m}}^{{\bf{ - 1}}}}$

Aromatic group (benzene)

${\bf{(C - H)}}$ stretching ${\bf{3030 c}}{{\bf{m}}^{{\bf{ - 1}}}}$

${\bf{(C = C)}}$ stretching ${\bf{1600 c}}{{\bf{m}}^{{\bf{ - 1}}}}$