The effect of structure on hydrogen bonding: Hydrogen bonded lactam dimers in CCl4

We have used both solution IR and NMR spectroscopies to investigate the hydrogen bonding of lactam dimers in CCl4. A series of lactam rings, from four- to eight-membered were investigated. Equilibrium constants for the formation of the cyclic hydrogen bonded dimer were obtained as a function of temperature in order to examine the effect of lactam ring size upon the enthalpy and entropy changes upon complexation. The resulting thermodynamic values for complexation do not follow the same trend with ring size as the equilibrium constants. It is also found that entropy plays an important role in determining the relative stability of a complex for a given ring size.