Effect of intramolecular hydrogen bonding of protonated normal primary and α,ω–diamines on the structure and exchange affinity of 18–crown–6-amine host-guest complexes in gas phase

The effect of intramolecular hydrogen bonding on the thermodynamics of the host–guest interactions have been investigated through the gas phase exchange studies of protonated normal primary amines and α,ω–diamines with ammonium ion in 18–crown–6 (18C6) cavity using ion mobility spectrometry (IMS). The results show that the tendency of diamines to interaction with 18C6 is lower than the normal amines due to the intramolecular hydrogen bond formation. The exchange constants of diamines to interaction with 18C6 follows the order 1,2–diaminoethane (1,2–DAE) 1,3–diaminopropane (1,3–DAP) 1,5–diaminopentane (1,5–DAP) 1,4–diaminobutane (1,4–DAB). This trend indicates that the most stable intramolecular hydrogen bond is formed in 1, 4–BDA through the formation six-member cycles.