Interrelation of nonequivalent CC bonds of naphthalene frame and spatial orientation of substituents: Beta-naphthalene sulfonyl fluoride and beta-naphthalene sulfonyl chloride

• Structure of β-naphthalene sulfonyl fluoride and chloride was determined.
• Each compound exists as two conformers which are enantiomers.
• Cβ-SHal plane deviates from perpendicular orientation relative to naphthalene frame.
• Peculiarities of the molecular structure were explained by NBO analysis.

β-naphthalene sulfonyl fluoride, β-NaphSF, and β-naphthalene sulfonyl chloride, β-NaphSCl, were studied by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 in combination with cc-pVDZ, aug-cc-pVDZ and cc-pVTZ basis sets). For each compound the calculations predicted the existence of two conformers which are enantiomers. On the basis of the experimental data it was found that the gas phase over β-NaphSF and NaphSCl at 357(5) K and 395(5) K, respectively, consists of molecular species of C1 symmetry in which the CβSHal plane deviates from the perpendicular orientation relative to the naphthalene skeleton plane. The following geometrical parameters (Å and degrees) were obtained from the experiment (uncertainties are in parentheses): rh1(CH)aver. = 1.097(7), rh1(CC)aver. = 1.410(3), rh1(CS) = 1.753(6), rh1(SO)aver. = 1.414(4), rh1(SF) = 1.559(5), ∠CCβC = 122.8(3), ∠CβSF = 103.3(30); Φ(CαCβSF) = 104(6) for β-NaphSF, and rh1(CH)aver. = 1.089(4), rh1(CC)aver. = 1.411(3), rh1(CS) = 1.757(5), rh1(SO)aver. = 1.419(3), rh1(SСl) = 2.053(4), ∠CCβC = 122.8(1), ∠CβSCl = 102.2(7), Φ(CαCβSCl) = 108(3) for β-NaphSCl. The calculated barriers to internal rotation of the sulfonyl halide groups exceed considerably the thermal energy values corresponding to the temperatures of the GED experiments. Natural bond orbital (NBO) analyses of the electron density distribution were applied to explain the peculiarities of the molecular structure of the studied compounds and the deviation from the structures of their benzene analogs.

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