N-Benzyl-2-propynamide

Pale-yellow crystals of the title compound, C10H9NO, have been obtained by the reaction of benzylamine and methyl propiolate. Weak intermolecular hydrogen bonding is observed between acetylenic H and carbonyl O atoms. The crystal packing is stabilized by these C—H⋯O and by N—H⋯O intermolecular hydrogen-bonding interactions.


Comment
The title compound is a terminal alkyne, which is an intermediate in the synthesis of triazole derivatives (Katritzky et al., 2002).
The molecular structure of the title compound is shown in Fig. 1. The bond lengths and bond angles in the compound are comparable to those in the structure of the methyl analogue (Leiserowitz et al., 1978). The atoms C1, C2, C3, O1, N1 and C4 of the title compound are nearly in a plane, and the r.m.s. deviation of these atoms from their mean plane is 0.007 Å. The dihedral angle between the plane of C5 and the phenyl ring and the mean plane of C1 to C4 and N1 is 76.8 (2)°. Hydrogen bonding plays a significant role in stabilizing the crystal structure; see Table 1 for geometric parameters and symmetry operations. The most prominent link occurs between the acylamide O and the N atoms, to form chains along the b axis.
Weak intermolecular hydrogen bonding is observed between the alkyne H and the carbonyl O atoms (table 1). Molecules are connected into a double chain by C-H···O and N-H···O intermolecular hydrogen-bonding interactions ( Figure 2).

Experimental
The title compound was synthesized using a similar synthetic method as for the preparation of 1-(pyrrolidin-1-yl)prop-2yn-1-one (Williamson et al., 1994). To a solution of benzyl amine (1.07 g, 10 mmol) in methanol (4 ml) was slowly added methyl propiolate (0.84 g, 10 mmol) at 195 K with stirring. After addition of the propiolate, the stirring was continued for 10 h and then the mixture warmed to 248 K for 5 h. The reaction was quenched with a saturated NH 4 Cl solution (12 ml) and extracted with ethyl acetate. The organic layer was washed with brine, dried over anhydrous MgSO 4 , concentrated under vacuum and the crude product was purified by column chromatography (petroleum ether: ethyl acetate, 2:1) to give the title compound as a pale yellow solid in 72% yield. Single crystals of the title compound were grown in a petroleum ether/ethyl acetate solution (v/v = 5:1) by slow evaporation.

Refinement
All non-hydrogen atoms were refined anisotropically. The acetylenic H atom was located from a difference Fourier map and both the position and isotropic thermal parameter were freely refined. The remaining H atoms were placed in ideal positions and refined via a riding model with N-H distances of 0.88, C-H methyelene = 0.99 and C-H aromatic = 0.95 Å and U iso = 1.2 U eq (C,N). Torsion angles were refined to fit the electron density. The metric parameters suggest the possibility of pseudo-merohedral twinning by a two fold rotation around either the a or the c axis. Application of the respective twin law of (-1 0 -0.43, 0 1 0, 0 0 1), obtained using the program Rotax (Parsons & Gould, 2003)) however indicated that the crystal at hand was not twinned.