Interplay between Conformation and Crystal Packing in Aryl Propargyl Ethers: Structural and Spectroscopic Properties of 2‐(prop‐2‐yn‐1‐yloxy)acene Derivatives

Abstract

The 2-(prop-2-yn-1-yloxy)naphthalene (compound I) and 1nitro-2-(prop-2-yn-1-yloxy)benzene (compound II) were prepared in excellent yields by the reaction of propargyl bromide with 2-naphthol and 2-nitrophenol, respectively. Structural and conformational properties of both compounds have been analyzed using a combined approach including single-crystal X-ray diffraction and quantum chemical calculations. Two forms are found to be stable and nearly isoenergetic conformers, depending on the mutual orientation of the C � C triple bond and the O-C single bond of the prop-2-yn-1-yloxy group. The gauche conformation is the most stable form for the vacuum isolated species, with the anti conformation higher in energy by 1.00 and 1.89 kcal/mol computed at the M06-2X/6-311 + + G(d,p) level of approximation, for I and II, respectively. The gauche form is observed in the crystal of I but the nearly planar anti conformation is adopted in the crystalline phase of compound II. The occurrence of C-H⋅⋅⋅π and C-H⋅⋅⋅O intermolecular interactions involving the acidic -C � C-H hydrogen donor and -C � C-and -OCH 2 -acceptors is discussed. Furthermore, vibrational features of the prop-2-yn-1-yloxy moiety are analyzed by infrared and Raman spectroscopy. The UV-Vis spectrum shows the presence of well-defined absorption at ca. 280 and 320 nm assigned to the π!π* transitions in the naphtyl/benzyl and prop-2-yn-1-yloxy groups, respectively.

Packing and Conformational Polymorphism in 1,2-Bis(aminocarbonyl(1-tert-butyl-1H-pyrazol-(3)5-yl))ethanes: Illuminating Examples of Highly Flexible Molecules

“…Thompson and Day also reported that flexible molecules often do not adopt their lowest energy form (global minimum) in crystal structures but rather the form that optimizes the balance of inter- and intramolecular interactions . In addition, the interplay between different conformers and the crystal structure of aryl propargyl ether derivatives was also attributed to intermolecular interactions …”

“…55 In addition, the interplay between different conformers and the crystal structure of aryl propargyl ether derivatives was also attributed to intermolecular interactions. 56 Insights into Supramolecular Packing. All compounds were analyzed at the supramolecular level focusing on polymorphs 1a and 2a,d to understand the packing of the obtained crystals.…”