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

ERBEN, MAURICIO F.; MICHAEL BOLTE; SYEDA SHEHZADI; MAURICIO ERBEN; AAMER SAEED; CARLOS A. FRANCA

ChemistrySelect

Wiley

Año: 2019 vol. 4 p. 9927 - 9933

2365-6549

The 2‐(prop‐2‐yn‐1‐yloxy)naphthalene (compound I) and 1‐nitro‐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 ‐OCH2? 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.