Effect of Polar Solvents on the Absorption Frequency of n→π Electronic Transitions

Abstract

A variety of spectroscopic data shows that the absorption frequencies of n→π electronic transitions progressively increase in the series of solvents, paraffin, alcohol, and water. This general effect of polar solvents on the frequency of n→π transitions is related to the characteristic change in the molecular charge distribution accompanying this type of transition. In certain cases solvation effects can be of considerable value in distinguishing between n→π and π→π electronic transitions. Evidence is presented which indicates that the absorption bands of the ions, NO₃⁻ (32,000 cm⁻¹), CO₃⁼ (46,000 cm⁻¹) and CS₃⁼ (20,000 cm⁻¹) are n→π transitions.