Synthesis , spectroscopic characterization and DFT calculations on [ 4-( sulfonylazide ) phenyl ]-1-azide

The title compound, [4-(sulfonyazide) phenyl]-1-azide has been synthesized and characterized by elemental analysis, IR, UV-Vis, Mass and NMR. Density functional theory (DFT) calculations have been carried out for the title compound by performing HF and DFT levels of theory using the standard 6-31G* basis set. The calculated results show that the predicted geometry can well reproduce the structural parameters. Predicted vibrational frequencies have been assigned and compared with experimental IR spectra and they support each other. The theoretical electronic absorption spectra have been calculated by using CIS, TD-DFT, ZINDO methods. C andH NMR of the title compound have been calculated by means of B3LYP density functional method with 6-31G* basis set. Comparison between the experimental and the theoretical results indicates that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties. On the basis of vibrational analyses, the thermodynamic properties of the title compound at different temperatures have been calculated.


Introduction
Organic azides are versatile starting materials for the synthesis of a variety of nitrogencontaining compounds that attracts the attention of both the organic and inorganic chemists.1, 3-Dipolar cycloadditions with the participation of organic azides have been turned into a valuable tool for the construction of heterocyclic compounds. 1The addition of 1, 3-dipolar species to unsaturated molecules for the synthesis of five-membered rings is a classical reaction in organic chemistry.These cycloadditions have been utilized for the preparation of compounds that are of fundamental importance in diverse fields of chemistry. 2][5][6][7] Inorganic chemists consider organic azides as readily accessible substrates for the preparation of nitrene (imido) complexes. 8Recently, the first successful isolation of complexes incorporating aryl, alkyl and arenesulfonyl azides as ligands has allowed us to take an insight into the chemical and structural features of complexes which have emerged so far only as elusive intermediates of organometallic reactions. 9Due to the practical and theoretical importance of organic azides, a variety of experimental methods and techniques have been used for their structural characterisation.These include IR 5 , NMR 10 and microwave 11 spectroscopy, electron diffraction 12 , mass spectrometry 13 and ab initio quantum chemical calculations. 146][15][16][17] The cross-linking reaction between hydrocarbons and sulfonyl azides isbelieved not to involve radicals, but to occur by an insertion reaction.Disulfonyl azides are, therefore, capable of cross-linking polyolefins with tertiary carbon atoms, such as polypropylene and polyethylene copolymers.As a part of our ongoing studies on sulfonyl azides [18][19][20][21] , in this paper we consider the synthesis and characterization of [4-(Sulfonylazide)phenyl]-1-azide (Figure 1).

Results and Discussion
The general route for the synthesis of [4-(Sulfonylazide)phenyl]-1-azide is shown on Scheme 1.The optimized structure parameters of this compound calculated by ab initio and DFT/B3LYP levels with the 6-31G* basis set are listed in Table 1.The aim of this study is to give optimal molecular geometry and vibrational modes of title compound.
The optimized configurations are shown in Figure 1.Since the crystal structure of this compound is not available, the optimized structure can be only being compared with other similar systems for which the configurations have been optimized. 22For example, the optimized bond lengths of C-C in phenyl ring fall in the range from 1.37783-1.39204Å for HF/6-31G* method and 1.38901-1.40271Å for B3LYP/6-31G* method, which are in good agreement with a similar molecular structure, (phenyl ring with arensulfonyl group) 1.385-1.400Å. 22 The optimized C ring -N bond length by two methods are 1.40669 Å for HF/6-31G* method and 1.41179 Å for B3LYP/6-31G* method, which is slightly shorter than that in compound with a similar molecular structure. 23For the bond of C ring -S, the optimized lengths (see Table 1) are slightly shorter than that in compound with a similar molecular structure (1.75906 Å for HF/ 6-31G* method and 1.78177 Å for B3LYP/ 6-31G* method). 23Based on above comparison, although there are some differences between our values and the literature data, the optimized structural parameters can well reproduce the literature ones and they are the bases for thereafter discussion.

Vibrational frequency
The observed experimental FT-IR spectra and theoretically predicted IR spectra are shown in Figures 2-4.The vibrational frequency and approximate description of each normal mode obtained using HF and DFT/B3LYP methods with 6-31G* basis set are given for this compound in Table 2.
In our study, vibrational frequencies calculated at B3LYP/6-31G* level were scaled by 0.96 and those calculated at HF/6-31G* level were scaled by 0.89. 20Gauss-view program 24 was used to assign the calculated harmonic frequencies.On the basis of the comparison between calculated and experimental results, assignments of fundamental modes were examined.The assignment of the experimental frequencies are based on the observed band frequencies in the infrared spectra of this species confirmed by establishing one to one correlation between observed and theoretically calculated frequencies.
The calculated frequencies are slightly higher than the observed values for the majority of the normal modes.Two factors may be responsible for the discrepancies between the experimental and computed spectra of this compound.The first is caused by the environment and the second reason for these discrepancies is the fact that the experimental value is an anharmonic frequency while the calculated value is a harmonic frequency. 25A linearity between the experimental and calculated wave numbers (i.e. for the whole spectral range considered), can be estimated by plotting the calculated versus experimental wave numbers (Figure 5).The values of correlation coefficients provide good linearity between the calculated and experimental wave numbers (correlation coefficients of 0.899-0.999).The benzene ring modes predominantly involve C-C bonds and the vibrational frequency is associated with C-C stretching modes of carbon skeleton.The C-C stretching modes, known as semi-circle stretching, predicted at 1510-1660 cm −1 is in excellent agreement with experimental observation of FT-IR value at 1520-1640 cm −1 .The ring breathing mode at 630 cm −1 coincides satisfactorily with a very weak band at 670 cm −1 . 26he aromatic structure shows the presence of C-H stretching vibrations in the region 2900-3150 cm −1 which is the characteristic region for the ready identification of the C-H stretching vibrations.In this region, the bands are not affected, appreciably by the nature of the substituents.The vibrations in the this region (2900-3150 cm −1 ) are in agreement with experimental assignment 2870-3130 cm −1 . 27,28 he out-of-plane bending of C-H predicted region of 1040-1060 cm −1 at B3LYP/6-31G*, while the calculations at HF level give the frequency values of 1050-1070 cm −1 , slightly on the higher side of expected region.
The calculations also show that the π(CH) vibrations are not pure and contain significant contributions of other modes (υ (SN) and π(CN)).The stretching υ(C-N) vibrations could be observed for the compound studied in a broad energy range, depending on the π-bonding nature of the C-N bond.Single σ(C-N) bonding appears, for the example, in the azoaromatic compounds.
The S-N stretching vibration exhibits a moderate band in the region 1010-1020 cm -1 , the band observed at this region is not pure υ (SN) vibration and contains a significant contribution of π(CH) mode.The observed bands 1320-1470 and 1100-1120 cm -1 were assigned to the υ(SO 2 )asym.and υ(SO 2 )sym.Modes, respectively.The bands at 510-530 cm -1 were assigned to, the SO 2 scissors and SO 2 wagging vibration, and have partly overlapped in this region, calculations show that ω (SO 2 ) vibration contains a considerable contribution with π ring. 29The major bands (630-890 cm -1 region) relate to S-C stretch.Exp.

Electronic absorption spectra
Experimental electronic spectra measured in dichloromethane solution along with the theoretical electronic absorption spectra calculated on the B3LYP/6-31G* level optimized structure are listed in Table 3.In addition, the theoretical electronic spectra have a broad band from 304 to 308 nm, which is different from the experimental peak at 312 nm.Molecular orbital coefficients analyses based on the optimized geometry indicate that the frontier molecular orbitals are mainly composed of p atomic orbitals, so electronic transitions corresponding to above electronic spectra are mainly LUMO and HOMO-LUMO for the title compound.Figure 6 shows the surfaces of HOMO (the highest occupied molecular orbital) and LUMO (the lowest unoccupied molecular orbital) So the electronic spectra are corresponding to electronic transition of the phenyl ring (transition of π-π* type).Absorption maxima (λ max ) for this compound were calculated by the CIS, TD, ZINDO methods.

NMR spectra
The experimental and theoretical values for 1 H, 13 C NMR, and calculated structural parameters of the title compound are given in Tables 4-5.We have calculated the theoretical 1 H, 13 C NMR chemical shifts, and structural parameters of the title compound.
The theoretical 1 H and 13 C NMR chemical shifts of compound have been compared with the experimental data.According to these results, the calculated chemical shifts and coupling constants are in compliance with the experimental findings.In order to compare the experimental chemical shifts, the correlation graphics based on the calculations have been presented in Figure 7.The correlation values carbon and proton chemical shifts are found to be 0.9913 and 0.9919 for HF and B3LYP with the 6-31G* basis set, respectively.
. Plot of the calculated vs. the experimental 13 C NMR, 1 H NMR chemical shifts (ppm).
As in Figure 8, this compound shows seven different carbon atoms, which is consistent with the structure on the basis of molecular symmetry.Due to that fact, in Figure 8, seven carbon peaks are observed in 13 C NMR spectrum of compound.If 1 H NMR spectrum (Figure 8) of the title compound is investigated, it can be seen that total number of protons are in agreement with the integration values presented in this spectrum.Chemical shifts were reported in ppm relative to TMS for 1 H and 13 C NMR spectra. 1 H and 13 C NMR spectra were obtained at a base frequency of 125.76 MHz for 13 C and 500.13MHz for 1 H nuclei. Relative chemical shifts were then estimated by using the corresponding TMS shielding calculated in advance at the same theoretical level as the reference.

Thermodynamic properties
On the basis of vibrational analyses and statistical thermodynamics, the standard thermodynamic functions: heat capacity (C o p,m ), entropy S o m and enthalpy H °om were obtained and listed in Table 6.Several calculated thermodynamic parameters are presented in Table 7. Scale factors have been recommended 31 for an accurate prediction in determining the zero-point vibration energies and the entropy.The total energies and the change in the total entropy at room temperature at different methods are also presented.) and 10 mL concentrated HCl wwere heated at reflux for 35 min, the resulting solution was cooled in an ice/salt bath to 0 °C.The solution was diazotized with a solution of sodium nitrite (0.76 g, 11 mmol) in water (20 mL), with the temperature maintained below 5 °C, and then stirred for a further 30 min in the cold.The solution was then neutralized with a saturated sodium bicarbonate solution.Sodium azide (15 mmol) in water (15 mL), was added slowly to a stirred suspension of (10 mmol) diazonium salt.After stirring for an additional 30 min, the mixture was further neutralized with a saturated sodium carbonate solution and then left to stir until precipitation was deemed to be complete (2-3 h).The solid product was filtered under suction, dried, and recrystallized from petroleum ether-dichloromethane give white-yellow solid.Yield: 65%; m.p. 37-39 o C [Ref. 36

Figure 6 .
Figure 6.Surfaces of HOMO, LUMO and HOMO-LUMO for the title compound.

Table 1 .
Selected bond distances (Å), bond angles ( o ) and torsional angles ( o ) of the title compound optimized

Table 2 .
Comparison of the observed and calculated vibrational spectra of the title compound

Table 4 .
Experimental and calculated 1 H NMR chemical shifts (ppm) of the title compound

Table 5 .
13perimental and calculated13C NMR chemical shifts (ppm) of the title compound

Table 7 .
35eoretically Sulfonylazide)phenyl]-1-azide has been synthesized and characterized by elemental analysis, IR, UV-Vis DFT calculations at B3LYP/6-31G* level for compound show that the optimized geometry closely resemble the crystal structure.The comparisons between the calculated vibrational frequencies and the experimental IR spectra indicate they support each other.The predicted electronic absorption spectra have some blue shifts compared with the experimental data and molecular orbital coefficients analyses suggest that the electronic spectra are assigned to π → π* electronic transitions.The experimental and the theoretical investigation of the title compound have been performed successfully by using NMR and quantum chemical calculations.Regarding the calculations, it is shown that the results of HF and B3LYP methods are in excellent agreement with all the experimental findings.Acetamidobenzenesulfonyl chloride (48.6 g, 208 mmol) was dissolved in 500 ml acetone and the solution was cooled to temperature of 0 o C over a period of 60 min.A chilled aqueous solution of sodium azide (20 g, 312 mmol, 200 ml) was added dropwise and the resultant solution allowed to stir for a further 60 min at that temperature.The solution was then poured onto an ice/water slurry (1.5 L) and the white precipitate was collected at the pump, washed with ice-cold water and dried under vacuum, 4-Acetamidobenzenesulfonyl azide could be used in the next step directly, recrystallized from a solution of acetone and water giving 4-Acetamidobenzenesulfonyl azide as white crystals, Yield: 75%; m.p. 108-110 o C; (Ref.35113-114o C); Analysis: calcd.C 40.01, H 3.36 N 23.32; found C 39.86, H 3.26, 23.22. 1 H NMR (DMSO-d 6 ): δ (ppm): 8.4 (1H, s, NH), 7.82 (H, d, J = 8.3 Hz, phenyl), 2.23 (3H, s, CH 3 ); 13 C NMR (DMSO-d 6 ): δ (ppm): 169.5, 144.1, 132.3, 128.9, 119.6, 24.7; FTIR (KBr) 2125, 1674, 1160 cm -1 ; m/z 240 (C 8 H 8 N 4 O 3 S).