Question

Question: Four infrared spectra are shown, corresponding to four of the following compounds. For each spectrum, determine the structure and explain how the peaks in the spectrum correspond to the structure you have chosen

Short answer

Answer

Step-by-step solution

IR-spectroscopy

Each organic functional group has a characteristic IR- absorption frequency. Based on that, the structure of the compound can be deduced.

Subpart (a)

The given spectrum indicates a broad peak at$3400 c{m}^{-1},-2500 c{m}^{-1}$ and confirms the presence of –OH group with C-H stretching.

A peak at$1710 c{m}^{-1}$ represents the C=O stretch in carboxylic acid.

A peak at $1660 c{m}^{-1}$represents C=C stretching.

From this data, it is clear that the given compound has the below shown structural formula:

Structure (a)

Subpart (b)

The given spectrum indicates the characteristic peak . This represents the C-H stretch.

A characteristic peak at$1710 c{m}^{-1}$ represents the C=O stretch.

Hence, the structure of the compound is as shown below:

Structure (b)

 Step 3: Subpart (b)

The given spectrum indicates the characteristic peak $3000 c{m}^{-1}-2840 c{m}^{-1}$. This represents the C-H stretch.

A characteristic peak at$1710 c{m}^{-1}$ represents the C=O stretch.

Hence, the structure of the compound is as shown below:

Structure (b)

Subpart (c)

The peak at$2900 c{m}^{-1}$ represents the presence of C-H stretch.

The peak at $2260 c{m}^{-1}$represents stretch.

The peak The peaks between $1600 c{m}^{-1}-1400 c{m}^{-1}$represents the C=C stretch in benzene.

Hence, the structure of the compound that represents the given IR spectrum is shown below:

Structure (c)

Subpart (d)

A characteristic broad IR peak $3500 c{m}^{-1}-3300 c{m}^{-1}$is observed .It represents the presence of O-H group.

A peak between $3000 c{m}^{-1}-2800 c{m}^{-1}$represents the C-H stretch.

The peaks between$1600 c{m}^{-1}-1400 c{m}^{-1}$ represents the C=C stretch in benzene.

Hence, the structure of the compounds for the given IR spectrum is as shown below:

Structure (d)