Question #f70e8

1 Answer
Nov 10, 2017

(E) The difference cannot easily be seen by IR.

Explanation:

(A) The peak at #"1700 cm"^"-1"# will disappear

Wrong. Both carboxylic acids and esters absorb at about #"1750 cm"^"-1"#, so you will see little change.

(B) The peak at #"3000 cm"^"-1"# will disappear

Wrong. The aromatic #"C.-H"# stretch occurs at #"3030 cm"^"-1"#, and this stretch is present in both compounds.

(C) There will be a new peak at #"2200 cm"^"-1"#

Wrong. This is the region where triple bonds and cumulated double bonds absorb. None of these are present in the product.

(D) There will be a new peak at #"3500 cm"^"-1"#

Wrong. This is the region of #"O-H"# stretching, and there are #"OH"# groups present in both compounds.

(E) The difference cannot easily be seen by IR

Correct. However, an experienced chemist could tell the difference.

A carboxylic acid has a very broad #"O-H"# absorption extending from #"2500 cm"^"-1"# to #"3300 cm"^"-1"#.

Carboxylic acid
(Adapted from the NIST WebBook)

A phenol has a narrower absorption from #"3200 cm"^"-1"# to #"3550 cm"^"-1"#.

Phenol
(Adapted from the NIST WebBook)