Quantum Mechanical Study on Hydrogen Bonds between 3-Aminophenol and CH_xCl_4 − x (x = 1, 2, 3): Effect of the Number of Halogen Atoms^#

Hydrogen bonds between 3-aminophenol and three chlorine-substituted methanes (CHCl₃, CH₂Cl₂, and CH₃Cl) were quantum mechanically studied at MP2/aug-cc-pVDZ level. Several low-energy structures with a hydrogen bond were identified for all chlorinated methanes, and the properties of their CH stretching vibrations were investigated. When it is hydrogen-bonded to 3-aminophenol (3AP), the CH stretching frequency of CHCl₃ is blue-shifted by 18–54 cm⁻¹, and its IR absorption intensity is 48–74 times increased, depending on the isomer. The symmetric and antisymmetric CH stretches of CH₂Cl₂ and CH₃Cl are shifted in either direction by a few cm⁻¹ upon hydrogen-bonding to 3AP, and their IR intensity was increased by a few times. It is concluded that all chlorinated methanes can make a π-hydrogen bond to 3AP but only CHCl₃, the one with the most chlorine atoms, makes a blue-shifting hydrogen bond, or an “antihydrogen bond”.