3-(2-Chloro-ethyl)-2-methyl-4H-pyrido[1,2-a]pyrimidin-4-one.

In the title mol-ecule, C(11)H(11)ClN(2)O, the pyrido[1,2-a]pyrimidine ring system is planar (maximum deviation = 0.0148 Å) and the methyl C and carbonyl O atoms are nearly coplanar to it. The chloro-ethyl side chain is in a synclinal conformation, nearly orthogonal to the pyrimidine ring, with a dihedral angle between the chloro-ethyl side chain and the pyrimidine ring of 88.5 (1)°. Weak inter-molecular C-H⋯N and C-H⋯Cl hydrogen bonds along with π-π inter-actions between the pyrimidine and pyridine rings [centroid-centroid distance is 3.538 (2) Å] form a three-dimensional network. The crystal is a racemic twin with a 0.68 (12):0.32 (12) domain ratio. MOPAC AM1 and density functional theory (DFT) theoretical calculations at the B3-LYP/6-311+G(d,p) level support these observations.