Structures and Intriguing Conformational Behavior of 1- and 2‑Naphthalenesulfonamides As Determined by Gas-Phase Electron Diffraction and Computational Methods

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2015-03, Vol.119 (9), p.1502-1510
• Main Authors: Giricheva, Nina I, Petrov, Vjacheslav M, Dakkouri, Marwan, Oberhammer, Heinz, Petrova, Valentina N, Shlykov, Sergey A, Ivanov, Sergey N, Girichev, Georgiy V
• Format: Article
• Language: English
• Subjects: Electrons; Gases - chemistry; Molecular Structure; Naphthalenes - chemistry; Quantum Theory; Sulfonamides - chemistry
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp5067617

The saturated vapors of 1- and 2-naphthalenesulfonamides (1-NaphSA and 2-NaphSA) were studied by the gas-phase electron diffraction/mass-spectrometric method at 413(9) and 431(9) K. According to quantum chemical calculations (DFT/B3LYP and MP2 with cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ basis set) 1-NaphSA possesses four conformers with different orientations of the SO2NH2 fragment relative to the naphthalene frame and eclipsed or staggered orientation of the NH and SO bonds, whereas 2-NaphSA possesses only two conformers with different orientations of the NH and SO bonds. It was experimentally established that vapors over 1-NaphSA and 2-NaphSA exist predominantly (up to 75 mol %) of low-energy conformers of C 1 symmetry in which the CSN planes deviate from perpendicular orientation relative to the naphthalene skeleton with near eclipsed orientation of the NH and SO bonds of the SO2NH2 fragment. The following geometrical parameters (Å and degrees) of the dominant conformers were derived: r h1(CH) = 1.089(4), r h1(CC)av = 1.411(3), r h1(CS) = 1.761(10), r h1(SO)av = 1.425(3), r h1(SN) = 1.666(10), ∠CC1C = 119.8(2), ∠C1SN = 104.5(22), C9C1SN = 69.5(30) for 1-NaphSA; r h1(CH) = 1.083(5), r h1(CC)av = 1.411(3), r h1(CS) = 1.780(7), r h1(S–O)av = 1.427(4), r h1(SN) = 1.668(6), ∠CC2C = 123.0(3), ∠C2SN = 103.6(19), C1C2SN = 110(10) for 2-NaphSA. The connection between nonequivalence of the C–C bonds in the naphthalene frame and spatial orientation of the substituents SO2NH2 is discussed. Transition states between conformers and enantiomers were determined.