Acta Crystallographica Section C

Crystal Structure Communications

Volume 65, Part 2 (February 2009)

organic compounds

Acta Cryst. (2009). C65, o70-o75 [ doi:10.1107/S0108270108043060 ]

The influence of sulfur substituents on the molecular geometry and packing of thio derivatives of N-methylphenobarbital

A. Janik, A. Olech, A. Stasiewicz-Urban and K. Stadnicka

Abstract: The room-temperature crystal structures of four new thio derivatives of N-methylphenobarbital [systematic name: 5-ethyl-1-methyl-5-phenylpyrimidine-2,4,6(1H,3H,5H)-trione], C₁₃H₁₄N₂O₃, are compared with the structure of the parent compound. The sulfur substituents in N-methyl-2-thiophenobarbital [5-ethyl-1-methyl-5-phenyl-2-thioxo-1,2-dihydropyrimidine-4,6(3H,5H)-dione], C₁₃H₁₄N₂O₂S, N-methyl-4-thiophenobarbital [5-ethyl-1-methyl-5-phenyl-4-thioxo-3,4-dihydropyrimidine-2,6(1H,5H)-dione], C₁₃H₁₄N₂O₂S, and N-methyl-2,4,6-trithiophenobarbital [5-ethyl-1-methyl-5-phenylpyrimidine-2,4,6(1H,3H,5H)-trithione], C₁₃H₁₄N₂S₃, preserve the heterocyclic ring puckering observed for N-methylphenobarbital (a half-chair conformation), whereas in N-methyl-2,4-dithiophenobarbital [5-ethyl-1-methyl-5-phenyl-2,4-dithioxo-1,2,3,4-tetrahydropyrimidine-6(5H)-one], C₁₃H₁₄N₂OS₂, significant flattening of the ring was detected. The number and positions of the sulfur substituents influence the packing and hydrogen-bonding patterns of the derivatives. In the cases of the 2-thio, 4-thio and 2,4,6-trithio derivatives, there is a preference for the formation of a ring motif of the R₂²(8) type, which is also a characteristic of N-methylphenobarbital, whereas a C(6) chain forms in the 2,4-dithio derivative. The preferences for hydrogen-bond formation, which follow the sequence of acceptor position 4 > 2 > 6, confirm the differences in the nucleophilic properties of the C atoms of the heterocyclic ring and are consistent with the course of N-methylphenobarbital thionation reactions.

Formula: C₁₃H₁₄N₂O₂S, C₁₃H₁₄N₂O₂S, C₁₃H₁₄N₂OS₂, C₁₃H₁₄N₂S₃ and C₁₃H₁₄N₂O₃


	Structure factor file (CIF format) (143.2 kbytes) [ doi:10.1107/S0108270108043060/ln31202-TPsup2.hkl ] Contains datablock 2-TP

	Structure factor file (CIF format) (162.5 kbytes) [ doi:10.1107/S0108270108043060/ln31204-TPsup3.hkl ] Contains datablock 4-TP

	Structure factor file (CIF format) (137.4 kbytes) [ doi:10.1107/S0108270108043060/ln31202,4-DTPsup4.hkl ] Contains datablock 2,4-DTP

	Structure factor file (CIF format) (153.9 kbytes) [ doi:10.1107/S0108270108043060/ln31202,4,6-TTPsup5.hkl ] Contains datablock 2,4,6-TTP

	Structure factor file (CIF format) (132.6 kbytes) [ doi:10.1107/S0108270108043060/ln3120Psup6.hkl ] Contains datablock P

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