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

In the title mol­ecule, C11H11ClN2O, 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 chloro­ethyl side chain is in a synclinal conformation, nearly orthogonal to the pyrimidine ring, with a dihedral angle between the chloro­ethyl side chain and the pyrimidine ring of 88.5 (1)°. Weak inter­molecular C—H⋯N and C—H⋯Cl hydrogen bonds along with π–π inter­actions 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.