Crystal structure of 3-[2-(4-methylphenyl)ethynyl]-2H-chromen-2-one

The coumarin ring system in the title asymmetric alkyne, C18H12O2, is approximately planar (r.m.s. deviation of the 11 non-H atoms = 0.048 Å), and is inclined with respect to the methylbenzene ring, forming a dihedral angle of 33.68 (4)°. In the crystal, supramolecular zigzag chains along the c-axis direction are formed via weak C—H⋯O hydrogen bonds, and these are connected into double layers via weak C—H⋯π interactions; these stack along the a axis.


S1. Introduction
Coumarins are heterocycles presenting a wide range of different biological activities (Wu et al., 2009). As part of our ongoing interest in the synthesis of coumarin derivatives with biological activity (Stefani et al., 2012) the title compound was synthesized.

S2.2. Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H = 0.95 to 0.98 Å) and were included in the refinement in the riding model approximation, with U iso (H) = 1.2-1.5U eq (C).

S3. Results and discussion
The title compound, Fig. 1, is an asymmetric alkyne. The coumarin residue is approximately planar with the r.m.s.
deviation of the 11 non-hydrogen atoms being 0.048 Å; the maximum deviations from their least-squares plane are 0.078 (1) and -0.066 (1) Å for the C2 and O2 atoms, respectively. Overall, the molecule is non-planar as seen in the dihedral between the fused ring system and the methylbenzene ring of 33.68 (4)°.
The most closely related structure in the literature is of the derivative where the methyl group of the title compound has been replaced by an isopropoxy group (Elangovan et al., 2004). In this case, with the exception of the terminal methyl groups, the molecule is planar with the dihedral angle between the 11 non-hydrogen atoms of the courmarin residue the benzene ring being 0.88 (6)°.
Weak coumarin-C 6 -C-H···O(exocyclic) hydrogen bonding gives rise to a supramolecular chain aligned along the c axis, Table 1 and Fig. 2. The chains are connected into double layers, sustained by weak C-H···π interactions, that stack along the a axis with no specific interactions between them, Table 2  The molecular structure of the title compound showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level.