Quantum chemical investigation of the structure and stability of all geometric isomers and conformers of all tautomeric forms of thymine

Dimer Mechanism for the Tautomeric Conversion of 4-Amino-2-oxopyrimidine

“…From Table 1 it is also seen that the distribution of the charge on the pyrimidine ring atoms in the investigated tautomers follows a well defined pattern. In particular, the high negative charge (especially for tautomer 2) on the C (5) atom and positive charge on atom C (6) points to a regioselectivity of electrophilic and nucleophilic addition respectively and this is found to be in full agreement with literature data [10]. The charge on atoms N (1) and N (3) is significantly higher when it is found to be in the sp 3 -hybridized form 1 and 2.…”

“…Both semiempirical [1-3] and non-empirical [4][5][6] quantum-chemical methods have been widely used for the theoretical investigation of the tautomeric conversions of pyrimidine derivatives including cytosine (4-amino-2-oxo-1H-pyrimidine) [1]. Six possible tautomers of 4-amino-2-oxopyrimidine have been discussed in the studies [2,7].…”

Thin‐Film Properties of DNA and RNA Bases: A Combined Experimental and Theoretical Study

“…At the HF/ 6-31G** level, 3 a is predicted to be the energetically lowestlying form of thymine, which is in line with previous studies. [21,43,44] All other isomers are found to be 48-130 kJ mol À1 higher in energy. Because of the structural similarity to uracil, we would expect-besides the analogous behavior of the energetics-a similar description of the ionization potentials.…”

Barrier-free proton transfer induced by electron attachment to the complexes between 1‐methylcytosine and formic acid

“…In contrast to the neutral uracil [79][80][81][82][83] or thymine [84][85][86], which do not posses low-energy tautomers, three such low-energy isomers exist for cytosine and two for 1-methylcytosine (see Figure 1). In the latter case these tautomers constitute the amino and imino form of mC (see Figure 1).…”