Question

What can be said about the shape of the infrared stretch of the O-H functional group in a carboxylic acid. Pick the best answers.

Answer 1

The O-H stretch in a carboxylic acid is broad and low, typically shifted to the lower energy, long-wavelength side of the IR spectrum, sometimes overlapping with the C-H region, due to the interaction between the carbonyl and hydroxyl groups.

Step-by-step explanation:

The shape of the infrared stretch for the O-H functional group in a carboxylic acid is broad and low. This characteristic absorbance is due to the bond stretching vibration of the O-H group within the carboxyl group. The carboxylic acid group (-COOH) exhibits vibrational modes in the infrared spectrum that are influenced by the presence of both the carbonyl (C=O) group and the hydroxyl (-OH) group. As a result, the O-H stretch in a carboxylic acid is typically displaced to the right, falling into the long-wavelength side of the spectrum and sometimes overlapping with the C-H stretching region.

Physical properties of carboxylic acids, such as the influence of the carbonyl and hydroxyl groups, contribute to the IR spectroscopy features that distinguish them from other functional groups. Due to the polar nature of the carbonyl bond, it absorbs very strongly in IR, while the bond between carbon and hydroxyl also exhibits its own distinct absorption due to a periodic change in the dipole moment when it vibrates.

Answer 2

c) Very broad

Step-by-step explanation:

The options for this question are:

a) Weak?

b) Strong?

c) Very broad?

d) Comes to a double point?

e) Sharp?

We have to keep in mind that the O-H group has the ability to form intermolecular hydrogen bonds. When this happens the stretch O-H can be affected by this phenomenon. In the IR spectrum can be observed a very broad signal due to this. Therefore when we have functional groups like alcohol or acids we can expect this broad signal.