Hydrogen bonds. Part I. The ethynyl–H⋯O interaction in crystals of propargyl 2-bromo-3-nitrobenzoate

Abstract

Propargyl 2-bromo-3-nitrobenzoate crystals are monoclinic, space group P2₁, with two molecules of the ester in a unit cell of dimensions a= 4·07, b= 17·99, c= 7·24 Å, β= 91° 30′. The atomic parameters were adjusted by Fourier and least-squares methods and the final discrepancy R over 951 independent reflexions is 6·5%. In the crystal there is an intermolecular H(ethynyl)⋯O(carbonyl) distance of 2·39 Å and the C–H⋯O angle is 156°. When the ester is in dilute solution in carbon tetrachloride the C–H stretching frequency of the ethynyl group is at 3313 cm.^–1. The absorption shifts to 3262 cm.^–1 when ethyl acetate is added to the solution, and to 3200 cm.^–1 when dimethyl sulphoxide, a stronger proton acceptor, is added. In the solid state the acetylenic C–H stretch appears at 3266 cm^–1.