The vibrational and NMR spectra, conformations and ab initio calculations of aminomethylene, propanedinitrile and itsN-methyl derivatives

Abstract

The IR and Raman spectra of aminomethylene propanedinitrile (AM) [H2N--CH=C(CN)2], (methylamino)methylene propanedinitrile (MAM) [CHaNH--CH=C(CN)2] and (dimethylamino)methylene propanedinitrile (DMAM) [(CH3)2N--CH=C(CN)2] as solids and solutes in various solvents have been recorded in the region 4000-50 cm-~. AM and DMAM can exist only as one conformer. From the vibrational and NMR spectra of MAM in solutions, the existence of two conformers with the methyl grotip oriented anti and syn toward the double C-----C bond were confirmed. The enthalpy difference AH ~ between the conformers was measured to be 3.7 + 1.4 kJ mol -l from the IR spectra in acetonitrile solution and 3.4 + 1.1 kJ mol -I from the NMR spectra in DMSO solution. Semiempirical (AM1, PM3, MNDO, MINDO3) and ab initio SCF calculations using a DZP basis set were carried out for all three compounds. The calculations support the existence of two conformers anti and syn for MAM, with anti being 7.8 kJ mol -~ more stable than syn from ab initio and 8.6, 13.4, 11.6, and 10.8 kJ mol -~ from AM1, PM3, MNDO, and MINDO3 calculations, respectively. Finally, complete assignments of the vibrational spectra for all three compounds were made with the aid of normal coordinate calculations employing scaled ab initio force constants. The same scale factors were optimized on the experimental frequencies of all three compounds, and a very good agreement between calculated and experimental frequencies was achieved.KEY WORDS: Vibrational and NMR spectra; conformational analysis; enamines; semiempirical and ab initio calculations.

A new route to produce chitosan derivatives: nucleophilic vinylic substitution with ethoxymethylenemalononitrile

“…The signals at 75 ppm are related to the C3, C5 carbons and the signals at 24 and 174 ppm are assigned to methyl and carbonyl groups in the Ch structure due to incomplete deacetylation of chitin 56 . After the chemical modification additional signals at 52 ppm (tertiary carbon) and 166 ppm (methylene) were observed as in the spectrum in red, corroborating the FTIR data 55, 56 …”

“…3) confirms the success of the reaction, showing a sharp peak at 2213 cm −1 , corresponding to the stretching of the CN bond 49, 50 . Furthermore, the peaks at around 2880 cm −1 are attributed to the CH and CH 2 stretch and that at 1623 cm −1 is attributed to the CC group, 55 corroborating the chemical modification.…”

“…56 After the chemical modification additional signals at 52 ppm (tertiary carbon) and 166 ppm (methylene) were observed as in the spectrum in red, corroborating the FTIR data. 55,56 EA results…”