Infrared and 13 C NMR spectral studies of some aryl hydrazides: Assessment of substituent effects

A series of some aryl hydrazides have been synthesized. These hydrazides purities were analyzed by physical constants and spectral data. The assigned spectral group frequencies were correlated with Hammett substituent constants and Swain-Lupton parameters using single and multi-linear regression analysis. From the results of statistical analysis, the effect of substituents on the spectral group frequencies has been discussed

Thirunarayanan and Sekar have studied the effect of substituents by Hammett spectral correlations in benzofuranyl flavonols and pyrazoline derivatives [16,17]. Within the above view, there is no report available for the study of effect of substituents in the aryl hydrazides. Therefore the authors have taken efforts for studying the effect of substituents on the substituted benzohydrazide by infrared and 13 C NMR spectra.

1. General
The IR spectra (KBr, 4000-400 cm -1 ) of all compounds have been recorded on AVATAR-300 Fourier transform spectrophotometer. The Bruker AV400 NMR spectrometer operating at 100 MHz for 13 C NMR spectra in CDCl3 solvent, using TMS as internal standard.

Synthesis of substituted benzohydrazides
All substituted benzohydrazides have been synthesized and analyzed their purities by literature method [4]. The general structure of the synthesized benzohydrazide is shown in Fig. 1.

RESULTS AND DISCUSSION
In the present study, the authors have investigated the effect of substituents on the assigned spectral frequencies using Hammett equation with Hammett substituent constants and Swain-Lupton's [18] constants by single and multi-linear regression analysis.

1. IR spectral study
In infrared spectral study, the Hammett equation is applied for prediction of effect of substituents on the carbonyl and NH stretches with Hammett substituent constants. In this correlation, the Hammett equation was taken as, where ν is the frequency for the substituted system, ρ is the reaction constants in terms of intercept, σ is the substituent constants and ν o is the frequency for the parent member of the series. The assigned carbonyl and NH stretches (ν, cm -1 ) of all substituted benzohydrazide are presented in Table 1. The results of statistical analysis [9][10][11][12][13][14][15][16][17] are shown in Table 2. From the table 2, the correlation of νCO and NH stretches (ν, cm -1 ) of hydrazide derivatives were produced satisfactory correlation coefficient. Among these correlations the σ constant gave slightly better r values. Other constants gave more or less equal r values. Similarly they produced the satisfactory correlation for multi-regression analysis with Swain-Lupton's [18] parameters. The generated multi-regression analysis equations are shown in (2)(3)(4)(5).

2. 13 C 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 hydrazide have been correlated with reactivity parameters. Thus the Hammett equation was used in the form as shown in (6). Log δ = Log δ 0 + ρσ … (6)

ILCPA Volume 32
where δ 0 is the chemical shift of the corresponding parent compound. The assigned CO and C ipso carbon chemical shifts (δ, ppm) of hydrazides have been assigned and correlated with Hammett substituent constants using single and multi-linear regression analysis [9][10][11][12][13][14][15][16][17]. The results of statistical analysis are shown in Table 2. From Table 2, the correlation of CO carbon chemical shifts (δ, ppm) of hydrazides with Hammett σ, σ + , σ R constants and R parameters were satisfactory. The Hammett σ I constant and F parameter were fail in correlation. This is due to the inability of prediction of the effect of substituents on the carbonyl chemical shifts and is associated with the resonance-conjugative structure as shown in Figure 2.  International Letters of Chemistry, Physics and Astronomy Vol. 32 r = correlation coefficient; I = intercept; ρ = slope; s = standard deviation; n = number of correlated derivatives The correlation of C ipso carbon chemical shifts (δ, ppm) of hydrazides gave satisfactory correlation with Hammett substituent constants [9][10][11][12][13][14][15][16][17] and F and R parameters [18]. Among these correlations, the Hammett σ I constants gave slightly better r values. The other correlations are more or less uniform. The multi-linear correlation of CO and C ipso carbon chemical shifts (δ, ppm) of hydrazides were produced satisfactorily correlation coefficients.

CONCLUSIONS
A series of some aryl hydrazides have been synthesized and recorded their infrared and 13 C NMR spectra. The assigned spectral group frequencies were correlated with Hammett substituent constants and Swain-Lupton parameters using single and multi-linear regression analysis. In infrared spectral correlations, all regressions gave satisfactory r values. In 13 C NMR spectral correlations, the carbonyl carbon chemical shifts correlated satisfactorily with Hammett σ, σ + , σ R constants and R parameters. The correlation of C ipso carbon chemical shifts (δ, ppm) of hydrazides gave satisfactory correlation with Hammett substituent constants and F and R parameters. In multi-regression analysis all spectral data of the hydrazides gave satisfactory correlations.