X-ray Structures of 1-Ethynyl-2-Nitrobenzene and 1-Ethynyl-4,5-Dimethyl-2-Nitrobenzene: Correlation to the Enhanced Rate of Hydration and Investigation of the C–H···O Alkyne-Nitro Hydrogen Bonding

Abstract

The single crystal X-ray structures of 2-nitrophenylacetylene, 1, and 4,5-dimethyl-2-nitrophenylacetylene, 2, are presented. In both structures the nitro moiety is essentially coplanar with the benzene ring and interacts with the proximal alkyne which is slightly distorted. The crystal packing of both compounds is dominated by intramolecular alkyne-nitro C–H···O hydrogen bonds that are supplemented by weak arene C–H···O (nitro) hydrogen bonds. Compound 1 crystallizes in the monoclinic space group P21/c with a = 3.7874(5), b = 13.0673(16), c = 13.98174(17) A, β = 90.587(2) and Z = 4. The molecule is disordered over two sites with occupancy ratio of 88:12. Compound 2 crystallizes in the triclinic space group P-1 with a = 7.6080(5), b = 9.8811(6), c = 12.8240(8) A, α = 108.1760(10), β = 102.4170, γ = 96.6480(10) and Z = 4. The intermolecular interactions in both structures were dominated by alkyne-nitro and arene-nitro C–H···O hydrogen bonds. The structures of 2-nitrophenylacetylene and 4,5-dimethyl-2-nitrophenylacetylene display a strong nitro-alkyne intramolecular O···C interaction resulting in distortion of the alkyne and terminal alkyne-nitro CH···O intermolecular interactions.