The enthalpies of hydrogen bonding (ΔH h b ) and tautomeric transformation (ΔH t t ) of hydrophosphorylic compounds of different space groups have been determined. It was found that acyclic and six-membered cyclic phosphoric acids, except calicylic derivatives exist in a form with P(O)H fragment and have ΔH t t values in the gaseous phase of about 70 kJ mol - 1 ; 1,3,2-dioxophospholanic analogues are about 40 kJ mol - 1 .