As there are no thermodynamic studies on the 4-aminocoumarin tautomerization molecule, this study was done for the first time in the world. 4-Aminocoumarin molecule stability was studied in the gaseous state and it has two isomers (imino form and amino form). The theoretical study and based on the results of density functions theory (DFT), imino possess higher stability state compared with amino. The thermodynamic values (the change in entropy ∆S and the change in enthalpy ∆H) of the isomerization form of amino to imino revealed that the conversion is spontaneous and endothermic.. The results showed that wavelength for greatest absorption (λmax) of imino form is longer than amino and this is due to the formation of a new double bond which leads to the association distribution of the electronic density along the molecule in the imino form.
Keywords: 4-Aminocoumarin; entropy; enthalpy; HOMO; LUMO