Question

Alcohols, carboxylic acids and water exhibit a very broad o—h peak between 3200-2600 cm-1. broad peaks are typically associated with intermolecular interactions resulting in multiple bonding scenarios. what intermolecular interaction between the molecules of these three compounds might explain their broad peaks.

Answer 1

Association Effects in Alcohols:

                                                  A broad peak is found in the IR spectrum of Alcohols in the range of 3500 cm⁻¹. The broadness is mainly due to special class of association effect called as hydrogen bonding. Hydrogen bonding mainly occur between the most electronegative element (F, O or N) of one molecule and the the hydrogen atom (attached to most electronegative atom) of another molecule.

Association Effects in Carboxylic Acids:

                                                               In carboxylic acids the -COOH group is responsible for the broadness of peak in IR spectrum at around 2600-3400 cm⁻¹. This broadness again results from the association effects called as dimerization in which a dimer of carboxylic acid is formed.

Association effect in Water:

                                            The association effect found in water is also due hydrogen bond interactions as that found in case of Alcohols.