Acta Phys. -Chim. Sin. ›› 1988, Vol. 4 ›› Issue (05): 461-465.doi: 10.3866/PKU.WHXB19880505

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MINDO/3 STUDY OF THE TAUTOMERIC REACTIONS OF THE TAUTOMERS OF CYTOSINE Ⅲ. THE TAUTOMERIC REACTION OF N3-H-4-NH2-2-OXO-CYTOSINE AND 4-NH2-2-OH-ISOCYTOSINE

Hong Sanguo; Feng Wenlin; Fu Xiaoyuan*   

  1. Quantum Chemistry Laboratory; Dept. of Chem. Beijing Normal University
  • Received:1986-12-23 Revised:1987-05-25 Published:1988-10-15
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Abstract: The molecular structures of 4-NH_2-2-OH-isocytosine (for short, iso-lactim) and N_3-H-4-NH_2-2-OXO-cytosine (for short, iso-lactam) have been optimized by MINDO/3. Iso-lactam is more stable than iso-lactim by ΔE=4.9kcal mol~(-1).
The geometric parameters of the transition state have been optimized by Powell's procedure which is contained in MINDO/3 program. The reaction pathway of the iso-lactam<=>iso-lactim has been studied by K. Fukui's IRC theory. The activation energies are 43.4 kcal mol~(-1) and 38.5 kcal mol~(-1) for the forward and backward reaction, respectively. An electron transfer scheme has been suggested to explain the nature of the tautomeric reactions of the tautomers of cytosine.