Six closely related 4,6-disubstituted 2-amino-5-formylpyrimidines: different ring conformations, polarized electronic structures, and hydrogen-bonded assembly in zero, one, two and three dimensions.

In each of ethyl N-{2-amino-5-formyl-6-[methyl(phenyl)amino]pyrimidin-4-yl}glycinate, C(16)H(19)N(5)O(3), (I), N-{2-amino-5-formyl-6-[methyl(phenyl)amino]pyrimidin-4-yl}glycinamide, C(14)H(16)N(6)O(2), (II), and ethyl 3-amino-N-{2-amino-5-formyl-6-[methyl(phenyl)amino]pyrimidin-4-yl}propionate, C(17)H(21)N(5)O(3), (III), the pyrimidine ring is effectively planar, but in each of methyl N-{2-amino-6-[benzyl(methyl)amino]-5-formylpyrimidin-4-yl}glycinate, C(16)H(19)N(5)O(3), (IV), ethyl 3-amino-N-{2-amino-6-[benzyl(methyl)amino]-5-formylpyrimidin-4-yl}propionate, C(18)H(23)N(5)O(3), (V), and ethyl 3-amino-N-[2-amino-5-formyl-6-(piperidin-4-yl)pyrimidin-4-yl]propionate, C(15)H(23)N(5)O(3), (VI), the pyrimidine ring is folded into a boat conformation. The bond lengths in each of (I)-(VI) provide evidence for significant polarization of the electronic structure. The molecules of (I) are linked by paired N-H···N hydrogen bonds to form isolated dimeric aggregates, and those of (III) are linked by a combination of N-H···N and N-H···O hydrogen bonds into a chain of edge-fused rings. In the structure of (IV), molecules are linked into sheets by means of two hydrogen bonds, both of N-H···O type, in the structure of (V) by three hydrogen bonds, two of N-H···N type and one of C-H···O type, and in the structure of (VI) by four hydrogen bonds, all of N-H···O type. Molecules of (II) are linked into a three-dimensional framework structure by a combination of three N-H···O hydrogen bonds and one C-H···O hydrogen bond.