Density functional theory and ab initio molecular orbital calculations have been carried out to investigate the molecular structures and properties of all 19 chlorophenol congeners. The results have been delineanated systematically in terms of the position and the total number of chlorine substitutions. Intramolecular hydrogen bonding in ortho chlorophenols and the induction by the electron-withdrawing chlorine are identified as strongly affecting the stability, structure, and properties of these compounds. Ortho chlorophenols are found to be more stable than other isomers as a result of intramolecular hydrogen bonding. Correlations between the known acidities of chlorophenols and the molecular structures are presented. Ortho chlorophenols are more acidic than other isomers because of the large inductive effect of chlorine on the hydroxyl group in close proximity. For the same reason, the acidity of a chlorophenol increases with the number of chlorine substitutions. Major trends and variations in molecular structure and properties, including O-H and C-O bond lengths, O-H stretching and torsional frequencies, average C-C bond lengths, and C-Cl bond lengths, are discussed in light of the intramolecular hydrogen bonding and the induction of chlorine.