Spectral correlations in some substituted styryl ( E )-4-((2-oxopropyl) diazenyl) benzoic acids

A series of titled compounds were prepared and analyzed their purities by literature method. The infrared and NMR spectral group frequencies of the compounds were assigned and correlated with Hammett substituent constants, F and R constants using single and multi linear regression analysis. From the results of statistical analysis, the effect of substituents on the above spectral frequencies was discussed.


INTRODUCTION
Currently, scientists and chemists were paid more attention for utilizing the spectroscopic data for studying QSAR, QPR and QSR of organic molecules [1][2][3][4][5][6][7][8][9][10]. From these studies, the ground state configuration and the effect of substituents on the molecule have been evaluated [11]. Also the spectroscopic data were applied for predicting the behavior of electrochemical redox potential correlation [12], reaction transition state equilibrium [13], IC 50 value of drug molecule correlations [14], qualitative and quantitative estimation [15], enol-enone tautomerism [16]. Generally chalcones possess important biological activities such as anti-microbial [3], antidepressants [17], antiplosmodial [18], antiaids [19] and insect antifeedant activities [20][21][22]. Infrared spectra is a good instrument for analyzing the structure of organic molecules [11], qualitative and quantitative measurements [15], geometrical isomers, s-cis and s-trans equilibration of unsaturated ketones, antiand gaucheform of acyl compounds [1][2][3][4][5][6][7][8][9][10]. The NMR spectroscopic data were applied for predicting spatial arrangements of the E or Z isomers and conformers in unsaturated ketones, pyrazolines, n-acetyl pyrazoline, thiopyrazoline and it derivatives [6,7]. The effect of substituents on the above molecular conformations also studied through Hammett substituent constants, F and R parameters [8]. Thirunarayanan have studied QSAR and QPR study with spectral frequencies in thiadiazole-2-amines [8]. Joseph and his co-workers have studied the effect of substituents on dimethyl phenyl chalcones by Hammett equation with spectral data [23]. Sekar and Thirunarayanan have evaluated the spectral correlation in pyrazoline derivatives [24]. The substituent effects on oxazine-2-amines were studied using spectral data using single and multi-regression analysis [25]. Kamalakkannan et al., have investigated the substituent effects on 2-indolyl chalcones by electrochemical redox potential with Hammett equation [26]. Kalyanasundaram et al., have studied the effect of substituents on phenoxyphenyl chalcones through IR and NMR spectroscopic data [10]. Within the above view there is no reported in the literature for the QSAR and QPR study of substituted styryl (E)-4-((2-oxopropyl) diazenyl) benzoic acids in the past. Therefore the authors have taken efforts for studying the effect of substituent on the IR and NMR spectral data through Hammett equation using linear regression analysis.

1. General
All chemicals and solvents used in this present study were purchased from Sigma-Aldrich and Merck companies. The infrared spectra of all chalcones were recorded in SHIMADUZ Fourier Transform IR spectrophotometer using KBr disc. The NMR spectra of all compounds have been recorded in BRUKER AV 400 type spectrometer, using CDCl 3 as a solvent, 400 MHz frequency was applied for recording 1 H, 100 MHz for 13 C NMR spectra, taking TMS as standard.

Synthesis of substituted styryl (E)-4-((2-oxopropyl) diazenyl) benzoic acid derivatives.
The titled chalcones were prepared and their purities were analyzed by the literature method [27]. The general structure of the chalcones is illustrated in Fig. 1. The analytical and spectroscopic data of selective compounds are given below.

2. NMR spectral study
In nuclear magnetic resonance spectra, the 1 H or the 13 C chemical shifts (δ, ppm) depend on the electronic environment of the nuclei concerned. These chemical shifts of substituted styryl (E)-4-((2-oxopropyl) diazenyl) benzoic acid derivatives have been correlated with reactivity parameters. Thus the Hammett equation was used in the form as shown in (10).

2. 1. 1 H NMR spectral study
The 1 H NMR spectra of these synthesized substituted styryl (E)-4-((2-oxopropyl) diazenyl) benzoic acid derivatives under investigations were recorded in deuteriochloroform solution using tetramethylsilane (TMS) as internal standard. The chemical shifts of (δ, ppm) vinyl protons of these compounds have been assigned and tabulated in Table 1. The results of statistical analysis [1][2][3][4][5][6][7][8][9][10][11][12][23][24][25][26][27][28][29] were presented in Table 2. From the Table 2, the correlation of Hα chemical shifts (δ, ppm) of the chalcones were satisfactory for Hammett σ, σ + , σ R constants and R parameter. The Hammett σ I constant and F parameter were fail in correlation for these chemical shifts. Only the Hammett σ R constant gave satisfactory correlation with Hβ chemical shifts (δ, ppm) of the chalcones. The remaining Hammett substituent constants, F and R parameters were fail in correlations. This is due to the inability of effect of substituents on the vinyl protons of the chalcones and is associated with the resonance conjugative structure as shown in Fig. 2. The correlation of methylene protons (δ, ppm) of the chalcones were fail in correlation with Hammett substituent constants and F and R parameters. The reason for failure in correlation was stated earlier and it is associated with the resonance conjugative structure as shown in Fig. 2. All correlations gave positive ρ values. This means that the normal substituent effect operated in all systems.

2. 2. 13 C NMR spectra
In the present study, the chemical shifts (δ, ppm) of CO acid , keto and vinyl carbons of the synthesized chalcones derivatives have been assigned and are presented in Table 1. Attempts have been made to correlate the above said carbon chemical shifts (δ, ppm) with Hammett substituent constants, field and resonance parameters with the help of single and multiregression analyses to study the reactivity through the effect of substituents. The results of statistical analysis [1][2][3][4][5][6][7][8][9][10][11][12][23][24][25][26][27][28][29] are presented in Table 2. The δCO acid chemical shifts (ppm) gave satisfactory correlations with Hammett σ R substituent constants, R parameter. The remaining Hammett substituent constants and F parameters were fail in correlation. The correlation of δCO acid and δCα chemical shifts (δ, ppm) was fail in correlation for Hammett substituent constants and F and R parameters. The reason for failure in correlation was stated already and is associated with resonance conjugative structure as shown in Fig. 2. The δCβ chemical shifts (δ, ppm) of all ketones were satisfactorily correlated with Hammett substituent constants and F and R parameters. All correlations gave positive ρ values. This means that the normal substituent effect operates in all systems.

CONCLUSIONS
A series containing nine substituted styryl (E)-4-((2-oxopropyl) diazenyl) benzoic acid derivatives were prepared and analyzed their purities by reported method. The infrared CO acid , CO s-cis, keto , CO s-trans, keto and N=N stretching frequencies (ν, cm -1 ), 1 H chemical shifts (δ, ppm) of vinyl, methylene protons, 13 C chemical shifts (δ, ppm) of CO acid , CO keto and vinyl carbons were assigned and correlated with Hammett substituent constants and F and R parameters. The infrared CO acid , CO s-cis, keto stretching frequencies (ν, cm -1 ) were correlated satisfactorily. The CO s-trans, keto stretching frequencies (ν, cm -1 ) were correlated satisfactorily for Hammett σ, σ + , σ R constants and R parameters. The 1 H chemical shifts of Hα (δ, ppm) of vinyl protons were satisfactorily correlated with Hammett σ, σ + , σ R constants and R parameters. The Hβ (δ, ppm) of vinyl protons were satisfactorily correlated only with Hammett σ R constant. The 13 C chemical shifts (δ, ppm) of CO acid carbons were satisfactorily correlated with Hammett σ R constants and R parameters. The vinyl Cβ (δ, ppm) carbon chemical shifts of prepared compounds were satisfactorily correlated with Hammett substituent constants, F and R parameters.