The enthalpies of vaporization of different classes of tetracoordinated phosphorous compounds have been determined according to their enthalpies of solution in hexane and carbon tetrachloride. Good agreement of some values with literature data is established. The enthalpies of specific (hydrogen bond) interaction of derivatives having acid properties, with p-xylene, dioxan and acetone have been determined. The enthalpies of solvation of cyclic and acyclic derivatives of methylphosphonic acid in different solvents are analysed and discussed.