UV identification substitution position of pyrimidine ring

Pyrimidine is six-member heterocyclic compound that contains two nitrogen atoms at positions 1 and 3. Pyrimidine derivatives have showed various biological activities such as antimicrobial, antitumor, antifungal, the hypnotic and sedative activities. The oxopyrimidnes of the biological activity of the most possess substituents at the N 1 or N 3 position [1-11]. This paper presents identification the location of the N 1 and N 3 isomeric substituents of the pyrimidine derivatives. The UV spectroscopy was used for this purpose. This method is simple, economical and does not require large quantities of sample. The absorption maxima of the 1 and 3-substituted pyrimidine derivatives were sensitive to the addition of base. In alkaline solution the N 3-alkyl substituted uracil showed bathochromic shift, but the absorption maxima of N 1 analogs shift toward shorter wavelengths (the hypsochromic shift) (Figure 1, 2, 3). This was associated with the formation of monoanion, which was created as a result of dissociation of a proton from the nitrogen atom (Scheme 2). The results were compared with the results that may be obtained from the analysis of proton nuclear magnetic resonance 1 H NMR (Scheme 1, 3, 4). The NMR spectroscopy is a method much more precise and it can provide more information about the structure of the compound. By 1 H NMR is not always possible clearly distinguish between N 1 and N 3 isomers, in contrast to the UV spectroscopy.