The fine structures of 4-amino-6-hydroxy-,
4-amino-6-mercapto-, 4-amino-2-mercapto-, 2-amino-4-hydroxy-, and
2-amino-4-mercapto-pyrimidine are revealed by comparing their ultraviolet
spectra and ionization constants with those of their S- and 0-, or N- and
S-methyl derivatives. On the evidence here presented they appear to exist
largely in aqueous solution as the tautomers containing an amino group, namely:
4-amino-1,6-dihydro-6-oxopyrimidine, 4-amino-1,6-dihydro-6-thiopyrimidine,
4-amino-1,2(and 2,3)-dihydro-2-thiopyrimidine, 2-amino-1,4(and
3,4)-dihydro-4-oxopyrimidine, and 2-amino-1,6-dihydro-6-thiopyrimidine,
respectively. Syntheses of hitherto unknown methyl derivatives are recorded.
The structure of sodium octafluoroprotactinate(V), Na,PaFs. has been determined by X-ray diffraction methods and refined by full-matrix least-squares techniques. The crystals are of tetragonal symmetry,;in space group I4/mmrn (D4,,I7) with a = 5.493 and c = 10.970 8 ; Z = 2, Each protactinium atom is bonded to eight fluorine atoms which lie at the corners of an almost perfect cube. The Pa-F bond distance is 2.21 8. The sodium atoms are located between the PaFa3-cubes. Metal-fluorine and fluorine-fluorine distances have been calculated for the isostructural uranium and neptunium compounds, Na,U Fs and Na,NpF8, respectively.RESULTS obtained from X-ray powder photographs and reported1s2 for N%PaF, and Na,UF, suggest that the co-ordination around the central-metal atom should be an example of the hitherto unknown cubic arrangement. The crystal structure of Na,PaF, has, therefore, been examined by single-crystal X-ray methods in order to test this deduction EXPERIMENTAL
The ionization constants and ultraviolet
spectra of cytosine, of its appropriately methylated derivatives, and of
related compounds are used to indicate that its pre- dominant tautomeric form
in aqueous solution is 4-amino-1,2-dihydro-2-oxopyrimidine.
This is in sharp contrast to its recent formulation as a zwitterion on the
grounds of its nuclear magnetic resonance spectrum.
The ultraviolet spectrum of
4,6-dihydroxypyrimidine is compared with those of N-, O-, and 5-alkylated
derivatives of fixed structures corresponding to possible tautomeric forms. In
contrast to earlier suggestions in the literature, it is concluded that an
aqueous solution consists essentially of 1,4,5,6-tetrahydro-4,6-dioxopyrimidine
in equilibrium with a smaller amount of 1,4-dihydro-6-hydroxy-4-oxo-pyrimidine.
The existence of the active 6-methylene grouping within the ring is confirmed
chemically by a ready condensation of benzaldehyde with the pyrimidine in
aqueous solution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.