Computational Study on the Structure of N-( 2-Amino-benzoyl )-N ’-phenyl hydrazine

The hydrazide compound N-(2-Amino-benzoyl)-N’-phenyl hydrazine has been synthesized and characterized by H-NMR, C-NMR, IR and X-Ray determination. The molecular geometry and vibrational frequency values in the ground state have been calculated using the density functional methods HF and B3LYP with the 6-31G(d) and 6-31G+(d,p) basis sets. The calculated results show that the optimized geometry can well reproduce the crystal structure, and the theoretical vibrational frequencies and chemical shift values show good agreement with experimental values.


Introduction
Hydrazides are a class of compounds with wide applications especially as a ligand in preparation of new complexes [1].These compounds can be used in synthesis of novel heterocyclic compounds [2], pharmaceutical chemistry [3] and many other applications [4].
The chemistry of hydrazide derivatives has been investigated intensively in the last decade owing to antituberculosis activity [5] and vibrational analysis [6] as well as their use in analytical chemistry [7].
Understanding the conformational behavior and spectral properties of hidrazides would give detailed information about their chemical and biological activity.Because of the biological significance particularly in medicinal and enzyme chemistry hydrazides have recently become attractive to theoreticians as well as experimentalists.Experimental and theoretical research may become a very useful methodology to describe reaction mechanisms in organic chemistry [8].The C-N rotational barrier in hydrazide was predicted to be about 28-30 kcal/mol which is indicative of a significant partial p double-bond character of the C-N peptide linkage and an sp 2 nature of the central nitrogen atom, which would stabilize the planar structure of the molecules [9,10].
In this paper, we report the synthesis, characterisation and crystal structure of N-(2amino-benzoyl)-N'-phenyl hydrazine,( C 13 H 13 N 3 O), as well as theoretical studies using the HF and DFT/B3LYP levels of theory using the 6-31G(d) and 6-31G+(d,p) basis sets.We aimed to describe and characterize the molecular structure, and chemical shifts of N-(2amino-benzoyl)-N'-phenyl hydrazine, both experimentally and theoretically.A comparison of the experimental and theoretical spectra can be very useful in making correct assignments and understanding the basic chemical shift-molecular structure relationship.

Material and Measurements
All chemicals were purchased from Sigma-Aldrich or Fluka Chemical Company with a stated purity of greater than 99% and it was used as such without further purification.The FT-IR spectra were recorded in the region of 400-4000 cm −1 on Perkin-Elmer Spektrum 100 BX, FT-IR spectrophotometer.The spectrum was recorded at room temperature, with scanning speed of 30 cm −1 min −1 and the spectral resolution of 2.0 cm −1 .Melting points were determined in open capillary tubes using Electrothermal IA-9200. 1 HNMR spectra were recorded indeuterated chloroform using tetra methyl silane (TMS) as an internal reference standard on BRUKER DPX-400 NMR spectrometer.

Synthesis of N-(2-Amino-benzoyl)-N'-phenyl hydrazine
A solution of (0.1 mol) phenyl hydrazine in water and (0.1 mol) of isatoic anhydride was added and stirred for 4 hr.The mix was stirred and the temperature raised slowly until a moderate evolution of CO 2 gas occurred.This was usually between 60 o C and 70 o C.After letting the mixture cool to room temperature, it was poured over crushed ice.The solid product were collected by filteration then fractionally recrystallized from dilute dioxane to give of dark brown crystals of the title compound suitable for X-ray analysis.

Computational details
The structural and geometrical features of the hydrogen bonded compound of the title compound is studied extensively in this work by ab initio and DFT calculations with various basis sets: 6-31G(d) and 6-31G+(d,p) using the GAUSSIAN 03 series of programs [11].Full geometry optimisation of the studied hydrogen-bonded complexes was performed.The optimised geometrical parameters were compared with the available experimental data in order to establish the accuracy for the prediction of the geometrical parameters of hydrogenbonded complexes.The density functional (DFT) calculations in this work were carried out in the framework of Kohn-Sham density-functional theory [12] (DFT) with the nonlocal three-parameter gradient corrected exchange-correlation functional of Becke and Lee, Yang and Parr including partially exact HF-exchange (B3LYP) [13].

X-ray structure determination
Diffraction measurements were made on a Bruker ApexII kappa CCD diffractometer using graphite monochromated Mo K radiation ( = 0.71073 Å) at 293 K.The intensity data were integrated using the SAINT program [14].Absorption corrections were applied based on equivalent reflections using SADABS [15].The structures were solved by direct methods and refined using full-matrix least-squares against F 2 using SHELXL [16].All non-hydrogen atoms were assigned anisotropic displacement parameters and refined without positional constraints.Hydrogen atoms were included in idealised positions with isotropic displacement parameters constrained to 1.5 times the U equiv of their attached carbon atoms for all others.
The program ORTEP-3 [17] for Windows was used preparation of the figures.Details of the data collection conditions and the parameters of the refinement process are given in Table 1.N-N-bond distance equals to 1.39 Å.The influence of the substituents on the skeletal molecular parameters of the title compound seems to be negligibly small.The bond lengths determined from B3LYP methods are slightly higher than that obtained from HF method.
C=O bond lengths (O30-C11) should be elongated when the hydrogen bond to N23-H25, N26-H27 and N28-H29 is formed in the crystal structure -the experimental value is therefore larger than calculated.It is possible that the crystal formation may introduce their significant strain because of intermolecular interactions.For numbering of atoms refer Fig. 1 The selected bond angles are summarized in Table 3 For numbering of atoms refer Fig. 1 The bond angles and also the torsion angles C12-N28-N26-C11, N28-N26-C11-C10, The torsion angles determined from B3LYP methods are slightly higher than that obtained from HF methods.For numbering of atoms refer Fig. 1 As seen from Table 2, most of the optimized bond lengths are slightly longer than the experimental values, the bond angles and dihedral angles are slightly different from the experimental angles.We note that the experimental results are for the solid phase and the theoretical calculations are for the gas phase.In the solid state, the existence of a crystal field along with the intermolecular interactions connect the molecules together, which results in the differences in bond parameters between the calculated and experimental values [20].

Vibrational analysis
The observed and calculated frequencies using HF/6-31G(d), HF/6-31+G(d,p), The aromatic ring carbon-carbon stretching modes are expected in the range from 1650 to 1200 cm −1 .Benzene has two degenerate modes at 15984 cm −1 and 1492 cm −1 .Similarly the frequency of two non-degenerate modes observed at 1307 cm −1 and 1031 cm −1 in benzene.
The actual positions of these modes are determined not so much by the nature of the substituents but by the form of substitution around the ring.The frequency of degenerate pair in benzene is fairly insensitive to substitution.
Conjugation, ring size, hydrogen bonding, steric and electronic effects often result in significant shifts in -C=O absorption frequencies [21].In the frequency of the carbonyl stretching vibration is absorbed at 1642 cm −1 in the infrared spectrum, the reason being that the double bond character of the -C=O group is less due to the nitrogen lone pair electron being delocalized towards the carbonyl end.
In the experimental frequencies observed at 3429 cm −1 in the infrared spectrum are assigned to the asymmetric stretching modes of N-(2-Amino-benzoyl)-N'-phenyl hydrazine.
Among the other vibrations of amino group, the very strong band in IR at 1612 cm −1 is assigned to the -NH 2 deformation mode.The N-H stretching vibration of hydrazide group appears at 3334 cm −1 and two different frequencies are calculated at this value.The in-plane bending vibration of the same is observed at 1584 cm −1 in the IR spectrum.This vibration is overlapped with the C-N in-plane bending absorptions.On the other hand, the two NH 2 stretching modes were assigned to the calculated whole metods.The strong vibrational frequency observed at 668 cm −1 in the infrared spectrum is assigned to the N-H out of plane bending mode of N-(2-Amino-benzoyl)-N'-phenyl hydrazine.The experimental values at all levels of calculations become slightly lower than the theoretical N-H stretching frequencies.
The theoretical values are given in Table 5.
Generally, 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 the title compound.The first is caused by the environment and second reason is the fact that the experimental value is an anharmonic frequency and while the calculated value is a harmonic one.

B3LYP/ 6 -
31G(d) and B3LYP/6-31+G(d,p) methods along with their relative probable assignments of N-(2-Amino-benzoyl)-N'-phenyl hydrazine are summarised in Tables 5.The maximum number of values determined by B3LYP/6-31G(d) method is well agreed with the experimental values and is also confirmed by the scale factors used to get the scaled frequencies.

Table 1 .
[18]tal data and structure refinement for compound 1.The selected bond distances are summarized in Table1.It is obvious that the C11-O30 with a bond length of 1.24 Å is in good agreement with the C=O double bond[18].The 1.36-1.40Åwhich is indicative of significant conjugate double bond character.The longer C10-C11 bond distance (1.48 Å) shows that there is no delocalization of the nitrogen lone pair of electrons towards the ring.From the structural data given in Table2it is observed that the various ring C-C bond distances and the C-H bond lengths of the title compound are found to be almost same at all levels of calculations.

Table 5 .
Experimental and calculated level vibrational frequencies (cm -1 ), and probable assignments of N-(2-Amino-benzoyl)-N'-phenyl hydrazine.deformation;as, antisymmetrical; oop, out of plane;  in-plane bending;  out of plane bending4.ConclusionsWe have carried out DFT and ab initio calculations on the structure and vibrational spectrum of N-(2-Amino-benzoyl)-N'-phenyl hydrazine.Comparison between the calculated and experimental structural parameters for bond lengths and torsion angles indicates that B3LYP results are in good agreement with experimental values.The parameters for bond angles indicates that HF results are in good agreement with experimental values.Vibrational frequencies, Infrared intensities calculated by B3LYP/6-31G(d) method agree very well with experimental results.