Infrared and NMR spectral Hammett correlations in 4-(2-naphthyl)-5,6-dihydro-6-(substituted phenyl)- 4 H - 1,3-oxazine-2-amines

A series containing ten titled compounds have been synthesised and recorded the IR and NMR spectra. From the spectra the infrared νNH, C=N, C-O-C stretches, NMR chemical shifts of (δ, ppm) NH and C=N were assigned and correlated with Hammett substituent constants, F and R parameters using single regression analysis. From the results, the effects of substituent on the above spectral frequencies were discussed.


1. General
All chemicals and solvents used in this present study were procured from Sigma-Aldrich and Merck companies. The infrared spectra of all oxazine imines have been recorded in SHIMADUZ Fourier Transform IR spectrophotometer using KBr disc. The NMR spectra of all compounds were 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.

1. Infrared spectral study
In infrared spectral study, the νNH, C=N and C-O-C (cm -1 ) stretches of synthesized amines were correlated by the Hammett equation as shown in equation (1).
where ν o is the frequency for the parent member of the series.
Some of the infrared stretches were fail in correlation with Hammett constants, F and R parameters in single linear regression analysis. They are worthwhile when seeking in multi parameter correlation with σ I and σ R or F and R Swain-Lupton [30] parameters. The generated multi-regression analysis equations are given in (2)(3)(4)(5)(6)(7). (r = 0.924, n = 10, P > 90 %)

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 have Log δ= Log δ 0 + ρσ where δ 0 is the chemical shift of the corresponding parent compound. The assigned 1 H NMR δNH, 13 C NMR δC=N (ppm) chemical shifts of 4-(2-naphthyl)-5,6-dihydro-6-(substituted phenyl)-4 H-1,3-oxazine-2-amines were presented in Table 1. These data were correlated with Hammett substituent constants, F and R parameters linear regression analysis [1][2][3][4]8,[27][28][29]. The result of statistical analysis was presented in Table 2. From Table 2, the δNH (ppm) chemical shifts of 4-(2-naphthyl)-5,6-dihydro-6-(substituted phenyl)-4 H-1,3-oxazine-2-amines were satisfactorily correlated with Hammett substituent constants and R parameters. The Field effect of the substituents were fail in correlation and it unable to predict the reactivity on the NH chemical shifts. This is due to the reason stated earlier and associated with Figure 1. All correlations gave positive ρ values. This means that then normal substituent effects operates in all systems.
From Table 2, the 13 C NMR δC=N (ppm) chemical shifts of 4-(2-naphthyl)-5,6dihydro-6-(substituted phenyl)-4 H-1,3-oxazine-2-amines were satisfactorily correlated with Hammett σ and σ + constants produce satisfactory correlations excluding 3-Cl substituent. The Hammett σ I , σ R substituent constants, F and R parameters were fail in correlation. This is due to the inability of substituent constants for prediction of reactivity on the chemical shifts of oxazine amines and associated with resonance conjugative structure shown in Fig. 1. All correlations gave positive ρ values. This means that then a normal substituent effect operates in all systems.
In view of the inability of prediction of effect of substituents by single regression analysis with Hammett substituent constants, F and R parameters, they are worthwhile when seeking in multi-regression analysis for 1 H NMR δNH, 13

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ILCPA Volume 27 oxazine amines were assigned and correlated with Hammett substituent constants, F and R parameters. From the single parameter correlation analyses, the infrared νNH, C=N (cm -1 ) stretches and NMR δNH and δC=N (ppm) chemical shifts correlated satisfactorily with Hammett substituent constants, F and R parameters. All the above spectral frequencies were satisfactorily correlated with σ I and σ R or F and R Swain-Lupton parameters in multiregression analysis.