Effect of substituents on phenazine derivatives by spectral studies

A series of eleven substituted dipyrido[3,2-a; 2 ′ ,3 ′ -c]phenazine derivatives have been synthesized and examined their purities by literature method. The infrared and 13 C NMR spectral data of prepared phenazines were correlated with Hammett substituent constants, F and R parameters using single and multi-regression analysis. From the results of statistical analysis, the effect of substituents on the infrared frequencies (ν, cm -1 ) and 13 C nmr chemical shifts(δ, ppm) has been studied.

Thirunarayanan and Sekar was studied the spectral qsar correlations in the pyrazoline derivatives [31]. The correlation study of infrared and 13 C-NMR chemical shifts of aryl hydrazides with Hammett substituent constants and F and R parameters were established by Thirunarayanan et al., [32] Mayavel et al., have investigated the spectral correlationslinearity of infrared and NMR spectral frequencies of carbazole imines with Hammett substituent constants, F and R parameters [33]. Sathiyendiran et al. [34] have prepared some 2oxopropy diazenyl benzoic acids and studied the spectral correlation. Recently Thirunarayanan et al have studied the spectral qsar study of phenazine derivatives [35]. There was no spectral correlation study was reported with phenazine molecules in the past. Therefore the author have taken efforts to prepare some substituted phenazines, recorded their infrared and 13 C NMR spectra for the spectral correlations study.

General
Merck and Sigma-Aldrich branded chemicals were used in this present study. The infrared spectra of all phenazines were recorded in SHIMADUZ Fourier Transform IR spectrophotometer using KBr discs. The 13 C NMR spectra of all compounds have been recorded in BRUKER AV 400 type spectrometer, using CDCl 3 as a solvent, 100 MHz for 13 C NMR spectra, taking TMS as standard.

Synthesis of substituted phenazine derivatives
The substituted phenazines were synthesized and the purities of the compounds were examined by literature method [1,[29][30][31]. The general structure of the substituted phenazine is shown in Fig.1. International Letters of Chemistry, Physics and Astronomy Vol. 48

RESULTS AND DISCUSSION
In the present study, the authors have investigated the correlation of infrared and 13 C-NMR spectral data of 10-and 11-substituted phenazines with Hammett substituent constants, F and R parameters using single and multi-linear regression analysis. Present investigation compound structure was shown is Fig. 1. This phenazines are symmetric molecule without substituents. When introducing the substituents at 10 and 11 th position, the symmetry will disturbed. With respect to C 15 =N 14 and C 6 =N 7 , the substituents attached in 11 th position was considered as metaand parapositions. Within the considerations, the authors have performed the assigned spectral frequencies were correlated separately with respect to C 6 =N 7 and correlations performed with respect to C 15 =N 14 systems in the phenazines.

Infrared spectral correlation
The assigned the C=N stretches (cm -1 ) of the present investigation substituted phenazines were tabulated in Table 1. These data were correlated with Hammett substituent constants, F and R parameters [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. In this correlation, the Hammett equation was employed as, where ν o is the frequency for the parent member of the series. The results of statistical analysis are tabulated in Table 2. From Table 2, the single parameter correlation of νC=N msubstituted pattern phenazines gave satisfactory correlation coefficients with σ, σ + , σ I constants and F parameters. Hammett substituent constants, F and R parameters except fluoro-substituent for σ I and R parameter excluding PhCO substituent. The Hammett σ R constants and R parameter were failing in correlations. Similarly the single parameter correlation of these stretches of psubstituted pattern phenazines gave satisfactory correlation with Hammett σ R constants and F parameters. The Hammett σ, σ + , σ I constants and R parameters were failing in correlations. All correlations gave positive ρ values. This meant that the normal substituent effect operates in all systems. The failure in correlation was due to the inability of predicting the substituent effects on the frequencies along with the resonance conjugative structure as shown in Fig. 2.

13 C NMR spectral correlation
The 13 C NMR chemical shifts of CN pyridine and phenazines moieties were assigned and are presented in Table 1. These chemical shifts were correlated with Hammett substituent constants, F and R parameters using single and multi-regression analysis [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. In these correlations, the Hammett equation was taken in the form as, δ = δ 0 + ρσ (2) Where δ 0 is the chemical shift of the corresponding parent compound. The results of statistical analyses are shown in Table 2. The correlations performed with respect to CN (m-substitution pattern), chemical shifts of δC=N pyri and phena (ppm) gave satisfactory correlation with σ and σ + and σ I constants F parameters gave satisfactory correlations except PHCO substituent. The Ipso carbon chemical shifts gave satisfactory correlation with Hammett substituent constants, F and R parameters. All correlations gave positive ρ values. These mean that the normal substituent effect operates in all systems. The reason for the failure in the correlation was already stated and along with the resonance conjugative structure as shown in Fig. 2.
The ipso carbon chemical shifts of the phenazines with Hammett σ R constant and R parameters gave satisfactory correlations. The Hammett σ, σ + , σ I constants and F parameter were fail in correlations. This is due to the inability of substituents along with conjugative structure as shown in Fig. 2.
The correlations performed with respect to CN (p-substitution pattern), chemical shifts of δC=N pyri (ppm) gave satisfactory correlation Hammett substituent constants, F and R parameters excluding PhCO substituent. The correlation of δC=N phena (ppm) with Hammett σ and σ + and σ I constants F parameters. The σ R and R parameters gave poor correlations for this chemical shifts. All correlations gave positive ρ values. These mean that the normal substituent effect operates in all systems. The reason for failure in correlation was already stated and it is associated with resonance conjugated structure as shown in Fig. 2. The Hammett gave satisfactory correlations except PHCO substituent. The Ipso carbon chemical shifts gave satisfactory correlation with Hammett substituent constants, F and R parameters.

ILCPA Volume 48
In single parameter correlations, some of the sigma constants gave poor correlations with were failed in correlations with Hammett substituent constants, F and R parameters. They are worthwhile when seeking multi-linear correlations with σ I and σ R constants or Swain Lupton's [36] F and R parameters gave satisfactory correlations for infrared and 13 C NMR spectral data of phenazines. The generated multi-regression analysis equations are shown in  Correlations

CONCLUSIONS
Totally nine substituted phenazines derivatives have been synthesized and their purities were examined by literature method. The infrared and 13 C NMR spectral frequencies of C=N, C-N and ipso carbons of the phenazines were assigned and correlated based on mand psubstituted system with Hammett substituent constants, F and R parameters using single and multi-regression analysis. Most of the correlations gave satisfactory correlation coefficients.