Studies on the Intramolecular Hydrogen Bond in Conjugated Systems by the Measurements of Dipole Moments. II. Salicylaldehyde and o-Hydroxyacetophenone

Dipole moments of 4-chloro-2-hydroxybenzaldehyde, 5-chloro-2-hydroxybenzaldehyde, 5-methyl-2-hydroxybenzaldehyde, p-chloroacetophenone, p-nitroacetophenone and 5-chloro-2-hydroxyacetophenone were measured in benzene solutions. Their values are 2.31D, 1.37D, 3.32D, 2.40D, 3.29D and 1.79D, respectively. The components of the dipole moments of salicylaldehyde and o-hydroxyacetophenone, which were evaluated from the components of the moments of phenol, benzaldehyde and acetophenone, do not agree at all with the components that satisfy the observed moments of salicylaldehyde and o-hydroxyacetophenone and their derivatives. The magnitudes of the discrepancies are about 1.1D in the x-direction for salicylaldehyde, about 2.3D in the x-direction for o-hydroxyacetophenone, and almost 0.0D in the y-direction for both compounds. It was concluded that the charge migration was caused from the hydroxyl oxygen to the carbonyl oxygen by the intramolecular hydrogen bonding.