(A)-See introduction for references (B)-See Tables and der Waals forces of an enthalpic nature. We have the enthalpy-dominated hydrogen bond limiting denaturation in the case of DNA chemical denaturation at experimental conditions of authors. Changes in DNA type and/or length and conditions of the experiment might lead to energetically different limiting steps in the chemical denaturation process related to the increased role of dispersion forces. This is the second possible explanation of differences in ∆H values for chemical and thermal processes.