The volume change on mixing (V^E) of binary systems of methanol (1) +n-butylamine, isobutylamine, sec. butylamine and tert. butylamine (2) were determined at 25‡ C by density method. All the four systems showed a large negative volume change on mixing and the maxima were observed nearly at 0.5 mole fraction. This was attributed to the possibility of 1 : 1 type of complex formation between amine and methanol. TheV^E was found to depend on the structure of butylamine and the magnitude ofV^E increased as tert.-BuNH₂ > sec.-BuNH₂ > iso-BuNH₂ >n-BuNH₂ This particular trend is attributed to increase in the number of amine-alcohol species formed on the mixing and the geometric fitting of methanol in the liquid structure of the butylamine.

Heats of mixing of the binary mixtures ofn-, sec-, iso- andt-butylamines with methanol were determined in the entire concentration range. All the four systems showed a strong exothermic behaviour. The exothermic heats of mixing vary in the ordert-BuNH₂ >n-BuNH₂ > sec-BuNH₂ > iso-BuNH₂. The enthalpy of hydrogen bond in the methanol-butylamine complexes was calculated by means of a thermochemical cycle and found to vary in the ordert-BuNH₂ >n-BuNH₂ > iso-BuNH₂ > sec-BuNH₂. This order is different than that found for the hydrogen bond due to self-association. The difference has been explained in the light of steric and electromeric effects arising out of the substitution of the methyl groups in the alkyl chain of the butylamine.

The excess volumes of four isomeric butanols with di-n-butyl ether were determined at 30°C. The isomeric effect was distinctly observed in the excess volume profiles. 1-Butanol and 2-methyl-l-propanol systems exhibited negative excess volumes throughout the concentration range. The 2-butanol system had positive excess volumes up to 0.9 mol fraction of alcohol after which it became negative, while the 2-methyl-2-propanol system exhibited positive excess volumes throughout the concentration range.