Density functional theory studies of pyrimidine bases thymine, cytosine and uracil

In the present investigation, HOMO-LUMO energy gap, polarizability, structural parameters, molecular mass, hardness, softness, chemical potential of the pyrimidine bases thymine, cytosine and uracil in the gas phase were calculated. Density Functional Theory calculations were performed by the B3LYP method with 6-311G basis set on the compounds. thymine, cytosine and uracil present polarizability of 70.45623, 64.75450 and 58.07109 a.u. at the B3LYP method, respectively. The HOMO–LUMO energy gap of 5.39343, 4.92623 and 5.56622 ev were obtained for the thymine, cytosine and uracil using B3LYP method, respectively. According to the calculations, HOMO–LUMO energy gap and hardness of uracil, polarizability of thymine, dipole moment and softness of cytosine in the gas phase have the largest values. According to the HOMO values, cytosine is more reactive in the reactions with electrophiles and according to the values of LUMO, uracil is more reactive against reactions with nucleophiles. N3 atom has the most negative charge and oxygen atoms have the highest electrical potential.