Spectra and hydrogen-bonding characteristics of thiocyanic acid. Part 3.—Thermodynamics of hydrogen-bonding with ethers

Abstract

Association constants for hydrogen-bonded complexes of iso-thiocyanic acid with a series of straight-chain, branched-chain and cyclic ethers in dilute carbon tetrachloride solution at 4, 25 and 40°C are reported. The data are based on measurement of the intensity of the unbonded N—H stretching vibration of HNCS, in a specially designed variable-temperature cell. The associated enthalpy and entropy changes are calculated; the former agree well with values determined calorimetrically for three cases studied by both methods. The thermodynamic data are discussed in relation to inductive effects, the frequency shifts of the fundamental vibrations of HNCS on bonding, ring size and possible steric effects. Ring opening reactions leading to the formation of hydroxythiocyanates are reported for the 3- and 4-membered cyclic ether systems.