Structures and Intriguing Conformational Behavior of 1- and 2

Article pubs.acs.org/JPCA

Structures and Intriguing Conformational Behavior of 1- and 2‑Naphthalenesulfonamides As Determined by Gas-Phase Electron Diffraction and Computational Methods Nina I. Giricheva,† Vjacheslav M. Petrov,† Marwan Dakkouri,*,‡ Heinz Oberhammer,*,§ Valentina N. Petrova,∥ Sergey A. Shlykov,∥ Sergey N. Ivanov,† and Georgiy V. Girichev*,∥ †

Ivanovo State University, Ivanovo 153025, Russia Department of Electrochemistry, University of Ulm, 89081 Ulm, Germany § Institut für Physikalische und Theoretische Chemie, Universität Tübingen, 72076 Tübingen, Germany ∥ Ivanovo State University of Chemistry and Technology, Ivanovo 153000, Russia ‡

S Supporting Information *

ABSTRACT: 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 C1 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: rh1(CH) = 1.089(4), rh1(CC)av = 1.411(3), rh1(CS) = 1.761(10), rh1(SO)av = 1.425(3), rh1(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; rh1(CH) = 1.083(5), rh1(CC)av = 1.411(3), rh1(CS) = 1.780(7), rh1(S−O)av = 1.427(4), rh1(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.

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INTRODUCTION

Several compounds that are most similar in terms of their structures, such as naphthalenesulfonyl halides,9,10 as well as benzenesulfonamide, BSA,11 and its derivatives, 4-methylbenzenesulfonamide (4-MBSA), 2-methylbenzenesulfonamide (2MBSA),12 and 2-nitrobenzenesulfonamide (2-NBSA),13 were studied earlier in our laboratory. Both BSA and 4-MBSA possess two conformers of Cs symmetry, in which the SN bond is orthogonal to the benzene ring plane, whereas the N H and SO bonds of NH2 and SO2 groups eclipse (eclipsed conformer) or stagger (staggered conformer) each other. On the other hand, 2-MBSA and 2-NBSA, possess four conformers, differing by the orientation of the SN bond relative to benzene ring plane (approximately orthogonal or approx-

Naphthalenesulfonamides are used as precursors for the synthesis of biologically active compounds, for plants’ protection, in syntheses of intermediate products and dyes, and some other important derivatives of naphthalenesulfonyl acids (anilides, esters, sulfones, etc.). Knowledge of structure and conformational properties of these compounds is important in the rationalization of their reactivity. In this paper, molecular structures of free naphthalenesulfonamide (NaphSA) molecules are reported. No data are available in the literature on the structure of these compounds neither in gas-phase, nor in the solid state. However, crystal structures of several composite organic compounds and complexes are known (see, for instance, refs 1−8), in which 1-NaphSA is a part of a ligand. Undoubtedly, the environment of the 1-C10H6SO2NH− fragment in the crystal affects the geometry and conformational properties of the molecule strongly. © XXXX American Chemical Society

Special Issue: 25th Austin Symposium on Molecular Structure and Dynamics Received: July 7, 2014 Revised: September 13, 2014

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dx.doi.org/10.1021/jp5067617 | J. Phys. Chem. A XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry A

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imately coplanar orientation) and by relative orientation of S O and NH bonds in the SO2NH2 group (staggered or eclipsed). The structures of all four conformers are obviously determined by the ortho-effect between the substituents, resulting in deviation of each substituent from its energetically most favorable position relative to the benzene ring plane. Quantum chemical calculations and results of gas-phase electron diffraction (GED) experiments show that eclipsed orientation of the NH2 group is preferable for all the benzenesulfonamides studied. Differences between structures of benzene and naphthalene are expected to cause differences in conformational properties and structures of BSA and NaphSA. In the present study, we investigate the structural and electronic properties of conformers of 1-NaphSA and 2- NaphSA.

Table 1. Conditions of the Synchronous GED/MS Experiments 1-NaphSA nozzle-to-plate distance, mm primary electron beam current, μA accelerating voltage,a kV temperature of effusion cell, K exposure time (average), s residual gas pressure in diffraction chamber, Torr scattering angles, Å−1 ionization voltage, V

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EXPERIMENTAL SECTION 1-NaphSA and 2-NaphSA were synthesized by the reaction of ammonia with the respective commercially available samples14 of naphthalenesulfonyl chlorides, NaphSCl, following the procedure described elsewhere.15 The applied samples of naphthalenesulfonyl chlorides were purified by repeated recrystallization from hexane/2-propanol mixture (80/20) until melting points of 65.0(0.2) °C (literature mp 66 °C16) and 75.0(0.2) °C (literature mp 76 °C16) were reached for 1NaphSCl and 2-NaphSCl, respectively. The final products 1NaphSA and 2-NaphSA were recrystallized twice from 20% aqueous solution of 2-propanol until melting points 148.0(0.4) °C (literature 150 °C and 214.0(0.4) °C (literature mp 217 °C) were achieved for 1-NaphSA and 2-NaphSA, respectively.16 The diffraction patterns were recorded using a combined EMR-100/APDM-1 apparatus, which allows carrying out synchronous gas electron diffraction and mass spectrometric (GED/MS) experiments.17,18 The sample was evaporated from a molybdenum effusion cell (ratio of the internal cylindrical part of the cell with the sample cross section to that of the effusion orifice was about 150). The temperatures of the effusion cell as measured by tungsten−rhenium W−Re 5/20 thermocouple were 413(9) and 431(9) K for 1-NaphSA and 2NaphSA, respectively. The accurate electron wavelength was calibrated against diffraction patterns of polycrystalline ZnO. The conditions of the GED/MS experiments are listed in Table 1. Interpretation of the mass spectra recorded simultaneously with diffraction patterns (Table 2) reveals that all registered ions originate exclusively from the molecular species 1-NaphSA and 2-NaphSA, respectively. No peaks were detected, which indicates any kind of thermal decomposition process or presence of volatile admixtures. The most intensive peak was that with m/e = 127 amu (C10H7+) in the mass spectra of both NaphSA compounds. This indicates that the predominant process of the dissociative ionization upon electron impact is the C−S bond cleavage. However, the molecular ion peak (m/e = 207 amu, C10H7SO2NH2+) is somewhat more intensive in 2NaphSA than in 1-NaphSA with 94% and 72% relative intensity, respectively. The intensive peak m/e = 143 amu (ca. 60%) demonstrates a high probability of an elimination process resulting in SO2 group emission. All other peaks with m/e < 127 amu correspond to destruction of naphthalene frame under electron impact. No mass spectra of 1-NaphSA or 2NaphSA are available from databases NIST19 and SDBS.20 Scattering intensities were measured with the modified MD100 microdensitometer (Carl Zeiss Jena).21 Experimental

2-NaphSA

338

598

338

598

1.4

0.6

1.4

1.3

96

94

96

96

417(5)

409(5)

435(5)

426(5)

95

45

110

85

1.1 × 10−6

2.4 × 10−6

1.6 × 10−6

2.0 × 10−6

3.4−31.4

1.3−17.6

3.2−31.3

1.3−17.8

50

50

a

Approximate value. Accurate wavelengths of electrons were calibrated using diffractions pattern of polycrystalline ZnO.

Table 2. Mass Spectra of the Saturated Vapor Phase over 1NaphSA and 2-NaphSA, Recorded at Uioniz = 50 V Simultaneously with the Diffraction Pattern abundance

a

ion

m/e, aua

1-NaphSA (1-C10H7SO2NH2)

2-NaphSA (2-C10H7SO2NH2)

C10H7SO2NH2+ C10H7SO2+ C10H7NH2+ C10H7+ C9H7+ C8H5+ C7H5+ C6H5+ C6H3+ C6H2+ C5H4+ or SO2+ C5H3+ C4H3+

207 191 143 127 115 101 89 77 75 74 64 63 51

72 6 59 100 32 12 5 22 14 14 11 12 14

94 9 60 100 31 17 5 29 16 16 10 13 12

For isotope of highest abundance.

molecular scattering functions were calculated as sM(s) = ((I(s) − G(s))/G(s))·s, where I(s) is the total experimental intensity, s is a scattering angle and G(s) is a background function.

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QUANTUM CHEMICAL CALCULATIONS The model of the 1-NaphSA molecule with atom numbering is shown at Figure 1. Prior to the electron diffraction analysis, a series of quantum chemical calculations were performed to estimate the starting values for conformational composition of the vapor phase, geometric, vibrational parameters of conformers and transition states (Figures 2 and 3). The methods DFT/B3LYP and MP2 in combination with cc-pVDZ, aug-ccpVDZ, cc-pVTZ, and aug-cc-pVTZ22,23 basis sets were used to determine the structural parameters of the conformers (Tables S1 and S2, Supporting Information). Determination of the barrier height between the conformers, as well as natural bond orbital (NBO) analyses of electron density distribution in the B



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Figure 1. Atom numbering of the 1-NaphSA molecule.

conformers and calculation of donor−acceptor interaction of the orbitals, were performed by employing the B3LYP approach. All theoretical calculations were performed by using the Gaussian 09 program package.24 For visualization of the geometric structure and molecular orbitals the Chemcraft25 program was applied.

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RESULTS AND DISCUSSION 1. Potential Functions for Internal Rotation of the SO2NH2 Group in 1-NaphSA and 2-NaphSA. Both 1-

Figure 3. (a) Potential functions V(C1C2SN) and (b) conformers of 2-NaphSA.

NaphSA and 2-NaphSA possess two nonrigid coordinates, associated with internal rotation of the SO2NH2 group around the C−S bond as well as of the NH2 group around the S−N bond. Torsional vibrations corresponding to these two coordinates are characterized by rather different values of frequencies. Thus, according to B3LYP/cc-pVTZ calculations the torsional vibration frequency of the SO2NH2 group around the CS bond in the most stable, eclipsed, conformer of 1NaphSA is 57 cm−1, which is much lower than that of rotation of the NH2 group around the SN bond, 153 cm−1. The latter vibration is related to the transition from eclipsed to staggered orientation of N−H and SO bonds of the SO2NH2 group. Analysis of potential energy distribution (PED) with respect to the internal coordinates shows that the nonrigid coordinate of the SO2NH2 torsional vibration is essentially uncorrelated with other modes. To determine conformational properties of the molecules, the potential functions for internal rotation of the SO2NH2 group around the CS bond were calculated. The torsional angle ϕ(CCSN) was varied in steps of 10°, and all other geometric parameters were fully optimized. The potential functions V(CCSN) for 1-NaphSA and 2-NaphSA are shown in Figures 2a and 3a. The relaxation of torsion angle ϕ(HNSO) within about ±8° was observed by scanning the torsion angle ϕ(CCSN) from 0° to 360°.

Figure 2. (a) Potential functions V(C9C1SN) and (b) conformers of 1-NaphSA. C



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Figure 4. Transition states between eclipsed and staggered conformers I → III and II → IV of 1-NaphSA.

Table 3. Calculated (B3LYP/cc-pVTZ/MP2/cc-pVTZ) Relative Total Energies ΔE, Relative Gibbs Free Energies, ΔG°T, for the Four Conformers of 1-NaphSA and for the Two Conformers of 2-NaphSA and the Relative Conformer Ratio χ in the Gas Phase at the Temperature of the GED Experiment 1-NaphSA I ΔE, kcal/mol ΔG°T, kcal/mola χ, mol %

ΔE, kcal/mol ΔG°T, kcal/mol χ, mol %

0/0 0/0 66/60

II 1.08/1.25 0.99/1.17 10/7 2-NaphSA

III

IV

0.453/0.09 0.88/0.52 23/32

2.91/2.75 2.78/2.62 1/1

I

II

0/0 0/0 76/68

0.59/0.23 1.00/0.64 24/32

Figure 5. Experimental (dots) and theoretical (line) molecular scattering intensity functions sM(s) and their differences ΔsM(s) for the optimal conformers ratio I:II:III/75:0:25 of 1-NaphSA.

a ΔG°T = G°T(k) − G°T(I). G°T(k): sum of electronic and thermal free energies of conformer k (k = II, III, IV). G°T(I): sum of electronic and thermal free energies of conformer I.

CSN). Possibly, electrostatic interaction between the amide hydrogens and the sulfonyl oxygens and the formation of O···H bonds (r(O···H) = 2.5 Å) is the reason for the stability of the eclipsed form. The predominance of the skewed conformer over the planar one is plausibly explained by the formation of intramolecular hydrogen bonding between one of the oxygen atoms of the SO2 group and the hydrogen of the C2−H bond of the type O2···H−C2. Such elucidation becomes evident when the closer proximity of the sulfonyl oxygen and the C2− H hydrogen, r(O2···H) = 2.35 Å and the natural charge on the interacting hydrogen of 0.27 e − are considered. For comparison, the remote H atoms on the naphthalene frame possess charges of 0.234 e− and in the unsubstituted naphthalene of 0.230 e−.

2. Conformers of 1-NaphSA and 2-NaphSA. The potential energy surface of 1-NaphSA possesses six minima (Figure 2a) of which I, I* and III, III* are the pairs of “skewed” enantiomers with eclipsed and staggered orientation of the N H and SO bonds, respectively. II and IV are “planar” conformers of Cs symmetry in which the S−N bond lies in the plane of the naphthalene frame. Thus, 1-NaphSA possesses four conformers, skewed eclipsed I, planar eclipsed II, skewed staggered III, and planar staggered IV (Figure 2b). According to our calculations, the eclipsed orientation of NH and SO bonds in the SO2NH2 substituent is energetically preferred relative to the staggered one at a given torsional angle ϕ(C D



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2-NaphSA. Transition states between enantiomers I → I* and II → II* in 2-NaphSA possess a structure of Cs symmetry with the S−N bond lying in the plane of the naphthalene frame. Transition I → II occurs by internal rotation of the NH2 group around the S−N bond with a barrier of 4.9 kcal/mol. 4. Relative Conformational Composition at the Temperature of the GED Experiment. Dashed horizontal lines in Figures 2a and 3a indicate thermal energy RT corresponding to the temperatures of the GED experiments (Table 1). According to our calculations, conformers I and III (1-NaphSA) and conformers I and II (2-NaphSA) lie in rather deep minima of the potential energy surface with rather high barriers between these conformers (see above). This justifies the use of rigid molecular models and a harmonic approximation in the analysis of the GED data. Relative total energies ΔE, relative Gibbs free energies ΔG°T for the four conformers of 1-NaphSA and the two conformers of 2-NaphSA, and the relative conformer ratios χ in the gas phase at the temperature of the GED experiment are summarized in Table 3. The ratios for 1-NaphSA were calculated from the ΔG°T values by taking into account that conformers I and II have enantiomers. These ratios indicate that three molecular forms have to be considered in the GED analysis for 1-NaphSA. In the case of 2-NaphSA both conformers can be present in the vapor at the temperature of the GED experiment. 5. Structural Analysis of GED Data for 1-NaphSA. The theoretical molecular scattering intensity function sM(s) for 1NaphSA was calculated under the assumption that the vapor phase contains three molecular forms, conformers I, II, and III (Figure 2b). The differences between homotypic bond distances and bond angles in the conformers were kept at the values predicted by B3LYP/cc-pVTZ calculations. The independent parameters were the following: five types of bond distances C−C, C−S, S−N, C−H, S−O (the N−H distance was refined in one group with the C−H distances), five bond angles C−C−C, C−C−S, C−S−N, C−S−O, O−S−N and the torsional angle C−C−S−N. Because, according to the quantum chemical calculations, the S atom lies in the plane of the naphthalene frame, the C−C−C−S torsional angle was fixed. Refinement of the torsional angle O−S−N−H resulted in a value with high standard deviation, −30 ± 21°, and was therefore fixed at −24.4°. All geometries are defined in terms of rh1 sructures and the vibrational corrections Δr = rh1 − ra were derived from the calculated force fields (B3LYP/cc-pVTZ) using the program package SHRINK,26−28 which takes a nonlinear relation between Cartesian and internal coordinates into account. Vibrational amplitudes for closely spaced internuclear distances were refined in groups, which were chosen according to the peaks in the radial distribution function. Molecular scattering intensities sM(s) and radial distributions f(r) for the optimized vapor phase composition are plotted in Figures 5 and 6, respectively. Several conformational ratios were tested in the least-squares analysis. The agreement factor Rf values corresponding to the refinement for some models of 1-NaphSA in the gas phase are shown in Table 4. According to the Hamilton criterion,29 the coefficient specifying a significance level of 0.05 for a data set described by 420 points and 28 variables is 1.049. This implies that all refinements with Rf values less than 4.082% are statistically indistinguishable. The following conclusions can be drawn on the basis of the analyses described in Table 4:

Figure 6. Experimental (dots) and theoretical (line) radial distribution functions f(r) and their difference Δf(r) for the optimal conformer ratio of 1-NaphSA.

Table 4. Agreement Factor Rf Values Corresponding to the Least-Squares Analysis for Some Vapour Models of 1NaphSA mole fraction, % skewedeclipsed

planareclipsed

skewedstaggered

vapor model

I

II

III

Rf , %

1 2 3 4a 5b 6

100 0 0 66 60 75

0 100 0 11c 8c 0

0 0 100 23 32 25

3.906 5.728 4.006 3.926 3.921 3.891

a

The values of mole fractions from B3LYP/cc-pVTZ calculations. The values of mole fractions from MP2/cc-pVTZ calculations. cSum of II and IV conformers mole fractions (Table 3). b

Corresponding potential functions for 2-NaphSA (Figure 3a) demonstrate the existence of two pairs of skewed enantiomers with eclipsed and staggered orientation of the NH and SO bonds. Therefore, 2-NaphSA possesses two conformers with C1 symmetry (Figure 3b), skewed eclipsed I and skewed staggered II. A planar conformation with the S−N bond in the naphthalene plane, as observed for 1-NaphSA, corresponds to a maximum in the potential function for 2-NaphSA. 3. Transition States between Conformers and Enantiomers. 1-NaphSA. Barriers of transition between the stable conformations I → II → I* and III → IV → III* were derived from the torsional potential functions of the SO2NH2 substituent around the C−S bond (Figure 2a). The barriers I → III and II → IV, i.e., between eclipsed and staggered orientations of NH2 and SO2, were obtained by the searching procedure for transition states (QST2). These barriers are 4.0 and 2.1 kcal/mol, respectively. It is surprising that transition I → III, i.e., from eclipsed to staggered orientation in the “skewed” conformation, occurs via internal rotation of the NH2 group around the S−N bond, whereas this transition in the planar conformation, II → IV, occurs via inversion of the NH2 group. The possible reason for this striking behavior is that the rotation of the NH2 group around the N−S axis in the planar conformation would result in a closer approach of the NH2 hydrogens and the hydrogen atom of the ring C2−H bond, thus leading to an increasing steric repulsion interaction between these hydrogen atoms (Figure 4). E



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Table 5. Experimental (of the Dominating Conformer I) and the Calculated (of Three Conformers) Structural Parameters of 1NaphSA (Atom Numbering in Figure 1) conformer I (skewed-eclipsed) parametera CH NH C1C2 C2C3 C3C4 C4C10 C9C10 C1C9 (CC)e CS SN SOe C9C1C2 C9C1S C1SN (C1SO)e (OSN)e C1SN C10C9C1S O1SNH mole fraction, % Rf, %

GED c

p1d

1.089(4) 1.023(4) (p1) 1.382(3) p2 1.418(3) (p2) 1.378(3) (p2) 1.426 (3) (p2) 1.442(3) (p2) 1.438(3) (p2) 1.411(3) 1.761(10) p3 1.666(10) p4 1.425(3) p5 119.8(2)c p6 122.6(5) p7 104.5(22) p8 108.9(12) p9 107.2(24) p10 69.5(30)c p11 −179.8 (fixed) −24.4 (fixed)

conformer III (skewed-staggered)

conformer II (planar-eclipsed)

theorb

theorb

theorb

1.079/1.080 1.013/1.014 1.372/1.380 1.408/1.407 1.367/1.375 1.416/1.415 1.431/1.433 1.428/1.423 1.400/1.402 1.799/1.777 1.684/1.670 1.453/1.449 121.8/122.0 122.4/121.9 102.7/101.3 108.8/108.7 107.4/107.7 66.6/64.9 −179.8/−179.8 −25.3/−31.5

1.079/1.081 1.012/1.013 1.372/1.379 1.408/1.407 1.368/1.375 1.416/1.415 1.432/1.433 1.428/1.423 1.401/1.402 1.807/1.784 1.672/1.659 1.449/1.445 121.6/121.8 122.3/121.6 106.5/105.3 108.3/108.2 105.7/106.0 69.0/66.8 −176.4/−175.5 52.5/54.5 25 3.89

1.078/1.081 1.012/1.012 1.371/1.379 1.409/1.408 1.367/1.375 1.416/1.414 1.430/1.432 1.428/1.424 1.400/1.402 1.800/1.777 1.679/1.664 1.454/1.450 121.6/121.8 118.3/117.6 103.9/103.3 108.2/108.0 107.4/107.6 180.0/180.0 180.0/180.0 3.6/4.6 0

75

a rh1 and re: structures are represented in the case of the GED and calculated parameters, respectively. bValues from (B3LYP/cc-pVTZ)/(MP2/ccpVTZ) calculations. cUncertainties given in parentheses were estimated as σ = (σscale2 + (2.5σLS)2)1/2 for distances, where the scale error σscale = 0.002r. σLS is a least-squares deviation; 3σLS for valence and 2.5σLS for torsion angles. dpi: refinable independent parameter. (pi): parameter refined in the ith group. eAverage value of internuclear distance or valence angles.

Figure 8. Experimental (dots) and theoretical (line) radial distribution functions f(r) and their difference Δf(r) for the optimal conformer ratio of 2-NaphSA.

Figure 7. Experimental (dots) and theoretical (line) molecular scattering intensity functions sM(s) and their differences ΔsM(s) for the optimal conformer ratio I:II (75:25) of 2-NaphSA.

(4) According to GED (model 6) and calculations (models 4 and 5), skewed conformers I and III dominate in the vapor phase and the mole fraction of the planar conformers is small. (5) The deviation of the S−N bond from orthogonal orientation relative to the naphthalene frame, as predicted by theoretical calculations for the conformers I and III, is confirmed by the GED analyses.

(1) The vapor phase consisting of exclusively planar conformer II describes the experimental data poorly (model 2 and Figure 2b). (2) The GED data do not allow a distinction between two skewed conformers, eclipsed I and staggered III. This is in accordance with the expectation for two reasons: (a) these conformers differ only by the orientation of the N− H bonds relative to the S−O bonds and (b) the scattering strength of the hydrogen atoms is minor. (3) The differences between mole fractions of the models 1, 4, 5, and 6 lead to negligibly small differences of corresponding structural parameters of the prevailing conformer I within the error limit given in Table 5.

The experimental structural parameters of the dominating conformer I and the calculated parameters of three conformers of 1-NaphSA are given in Table 5. 6. Structural Analysis of GED Data for 2-NaphSA. The theoretical molecular scattering intensity function sM(s) for 2F



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Table 6. Experimental (of the Dominating Conformer I) and the Calculated (of the Both Conformers) Structural Parameters of 2-NaphSA conformer I (skewed-eclipsed) parametera CH NH C1C2 C2C3 C3C4 C4C10 C9C10 C1C9 (CC)e CS SN SOc C1C2C3 C1C2S C2SN (C2SO)e (OSN)e C1C2SN C9C1C2S O1SNH mole fraction, % Rf, %

c

p1d

1.083(5) 1.014(5) (p1) 1.380(3) p2 1.424(3) (p2) 1.378(3) (p2) 1.430 (3) (p2) 1.439(3) (p2) 1.428(3) (p2) 1.411(3) 1.780(7) p3 1.668(6) p4 1.427(4) p5 123.0(3)c p6 118.5(11) p7 103.6 (19) p8 108.1(9) p9 107.4(28) p10 110(10)c p11 178.7 (fixed) 9.9 (fixed) 75(8) p12

conformer II (skewed-staggered)

theorb

theorb

1.082/1.082 1.013/1.013 1.368/1.375 1.412/1.411 1.369/1.374 1.419/1.416 1.427/1.430 1.416/1.414 1.399/1.401 1.789/1.769 1.683/1.668 1.453/1.449 121.8/122.2 119.2/119.0 103.0/101.7 108.1/108.2 107.2/107.5 109.7/110.1 178.7/179.4 9.9/13.8

1.081/1.082 1.012/1.012 1.370/1.377 1.413/1.411 1.368/1.376 1.418/1.415 1.428/1.431 1.415/1.413 1.400/1.402 1.796/1.777 1.672/1.659 1.449/1.445 121.6/122.0 119.4/119.1 106.9/105.9 107.7/107.7 105.6/105.8 98.3/96.2 −179.5/−178.3 50.9/51.5 25(8)

GED

3.77

a

rh1 and re: structures are represented in the case of the GED and calculated parameters, respectively. bThe slashed values are (B3LYP/cc-pVTZ)/ (MP2/cc-pVTZ). cUncertainties given in parentheses were estimated as σ = (σscale2 + (2,5σLS)2)1/2 for distances, where the scale error σscale = 0.002r. σLS is a least-squares deviation; 3σLS for valence and 2.5σLS for torsion angles. dpi: refinable independent parameter. (pi): parameter refined in the ith group. eAverage value of internuclear distance or valence angles.

Figure 9. Orbital interactions between the electron-donor orbital π(C1−C2) and the acceptor orbital σ*(S−N) in the most stable conformers of 1NaphSA (left) and 2-NaphSA (right).

NaphSA was calculated on the basis of the assumption that the investigated vapor phase contains two conformers (Figure 3b). Structural parameters of the molecule were refined along with the conformational ratio in the least-squares analysis. Assumptions were used analogous to those in the case of 1NaphSA (Table 3). Molecular scattering intensities sM(s) and radial distributions f(r) for the optimized vapor phase composition are plotted in Figures 7 and 8, respectively. The experimental structural parameters for the dominating conformer and the calculated values for both conformers of 2NaphSA are given in Table 6. Data collected in Tables 5 and 6 demonstrate that B3LYP and MP2 methods with the basis set cc-pVTZ predict for both molecules, 1-NaphSA and 2-NaphSA, C−C bonds to be about

0.01 Å shorter than experimental values and distances C−S, S− N, and S−O to be longer by 0.01−0.03 Å than experimental values. MP2 results are closer to the experiment. Both methods with cc-pVDZ, aug-cc-pVDZ basis sets reproduce the average C−C distances, but strongly overestimate the S−N and S−O distances by about 0.05 Å (Tables S1 and S2, Supporting Information). 7. Concluding Remarks. GED and quantum chemical studies of 1-NaphSA and 2-NaphSA demonstrate that these two compounds possess different conformational properties and a different number of conformers. However, most of the structural parameters of the dominant conformers I of both molecules differ only slightly (Tables 5 and 6). Thus, the average lengths of C−C bonds in the naphthalene skeleton, as G



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well as the S−N, S−O distances and valence angles of the SO2NH2 group, are equal in both compounds. The main differences are in the lengths of the C−C bonds adjacent to the substituent, as well as in the value of the torsion angle C−C− S−N. Deviation of the S−N bond from orthogonal position relative to the naphthalene frame by about 20° is characteristic for the most stable conformer of both compounds. In the case of 1-NaphSA, S−N bond is orientated toward the long C1−C9 bond and away from the short C1−C2 bond. Similarly, in 2NaphSA the S−N bond is directed toward the long bond (i.e., C2−C3) and away from the short C1−C2 bond. Therefore, it is apparent that the orientation of the S−N bond deviates in different directions from the short C1−C2 bond in 1-NaphSA and 2-NaphSA. Such a structural feature of sulfonyl substituted naphthalenes C10H7−SO2X was observed also in our recent study of 1NaphSCl and 2-NaphSCl.9,10 A natural bond orbital (NBO) analysis demonstrated that the sum of the donor−acceptor interaction energies between the orbitals of the naphthalene frame and the orbitals of the SO2X substituent depends on the C−C−S−X torsional angle. It was shown9,10 that the maximal stabilization energy occurs for a skewed position of the S−X bond and is inclined toward the longest C−C bond adjacent to the substituent. This is connected with the inhomogeneous electron density distribution along the naphthalene frame. Figure 9 shows the interactions between the donor π(C1−C2) and the acceptor σ*(S−N) orbitals, which contribute to the stabilization of the skewed conformers of 1-NaphSA and 2NaphSA. From this figure, it may be seen that the S−N bond adopts different orientations relative to the C1−C2 bond in 1NaphSA and 2-NaphSA. It should be pointed out that SO2X substituents in benzene, which possesses a homogeneous electron density distribution along the ring frame, are characterized by an exactly orthogonal position of the S−X bond relative to the ring.30−32 The stability of the planar conformer II of 1-NaphSA is mainly due to interactions between π(C1−C2) and σ*(SO) orbitals, which stabilizes the structure with Cs symmetry (Figure S1, Supporting Information). Moreover, it is worthwhile to point out that in the planar conformer the distance between the nitrogen atom of the amide group and the hydrogen atom of the C2−H bond is 2.40 Å. This represents an ideal requirement for an attractive electrostatic interaction between the nitrogen lone pair electrons and the positively charged hydrogen. An indication for such an interaction is sustained by the apparent increase of the positive charge of the involved hydrogen atom. The natural charge on the hydrogen of C2−H bond is about 0.26 e− in the planar conformation whereas the positive charges of the remote hydrogen atoms on the naphthalene frame vary between 0.23 e− and 0.24 e−.

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AUTHOR INFORMATION

Corresponding Author

*G. V. Girichev. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Deutsche Forschungsgemeinschaft and Russian Foundation for Basic Researches for financial support of the Russian-German Cooperation (grants DFG OB 28/22-1 and RFBR 12-03-91333-DFG_a) and The Ministry of Education and Science of The Russian Federation (Project Supporting Program) for financial support of structural analysis computations.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

Tables S1 and S2 include the experimental and calculated structural parameters (bond distances, valence and dihedral angles) of conformer I of 1-C10H7SO2NH2 and conformer I of 2-C10H7SO2NH2. Tables S3 and S4 include the experimental interatomic distances, experimental and calculated vibrational amplitudes, and vibrational corrections of conformer I of 1C10H7SO2NH2 and conformer I of 2-C10H7SO2NH2. Figure S1 elucidates the orbital interactions between the electron-donor orbital π(C1−C2) and the acceptor orbital σ*(S−O) in conformer II of 1-NaphSA. References 2 and 24 with the full H



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Structures and Intriguing Conformational Behavior of 1- and 2

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