B 3 LYP theoretical calculations and structure of 4-[ ( 2-{ [ ( 1 E )-1-methyl-3-oxobutylidene ] amino } ethyl ) imino ] pentan-2one

In this work we present the synthesis 4-[(2-{[(1E)-1-methyl-3-oxobutylidene]amino} ethyl)imino]pentan-2-one. We also propose evidence for the presence of various tautomers for this molecule, and theoretical density functional theory (DFT)-B3LYP/6-31G* calculations to characterize the potential energy surface of these species. NMR, IR, MS techniques and X-ray are also used to analyze the molecule 3 and its tautomeric preferential form.


Introduction
Metallo-organic complexes containing conjugated nitrogen ligands represent an important class of nonlinear optical chromophores. 1Efficient systems involving organometallic and coordination compounds with pyridine, 2 diimine, 3 salen-type 4 or Schiff-base ligands have been described. 5e have also demonstrated the direct impact of dipolar in drug design of functionalised bisarmed quinoxaline 6 and imidaz [1,2-a]pyridine (or pyrimidine) ligands. 7,8n connection with our research aimed at developing new pharmacophore site(s) leading us to efficient and selective antitubercular, 9 antitumoral 10 or anti-HIV drugs, 11 we became interested in the pharmacomodulation of parent drugs, as like the ethambutol; a clinical antitubercular agent.
The title compound (3) is a Schiff base.Compound (3) is a well known Schiff base 4,9dimethyl-5,8-diazadodeca-4,8-diene-2,11-dione, more commonly known as bis-(acetylacetone)ethylenediimine and abbreviated as H 2 baen.Compounds of this type can exist in six tautomeric forms (see scheme 2 below), i.e. a non-hydrogen-bonded keto-imine, a hydrogenbonded enol-imine and a hydrogen-bonded keto-amine and mixed forms.It has been shown by IR and 1 H-NMR evidence that in the solid state and in most common organic solvents H 2 baen exists completely as the hydrogen-bonded tautomers with at least 80% contribution from the keto-amine form. 14
1 H-NMR resonance for the ethylenediamine (N-CH 2 -CH 2 -N) group (at δ 3.4) is not a singlet as expected, but rather is a multiplet due to spin-spin coupling with the amine H atom present in the keto-amine tautomer (3b).Similar conclusions have been drawn for one analogue compound; the 3,10-di-[2-(2-pydidyl)-ethyl]-bis-(acetyl-acetone)ethylenediimine. 15t was of interest to compare the structural features of compound 3 implied by the spectral data with that actually existing in crystalline form to see which geometric conformer is dominant (cisoidal or transoidal conformers) as described in Scheme 3.
ARKAT USA, Inc.Since the spectroscopic properties of the compound 3 were limited to (NH-C=C-C=O) moieties, it was difficult to attribute or separate the two possible conformers.To have a clear idea about the conformational aspect of compound 3, see Figures 1 and 2.

Thermodynamic Calculations
In addition to the experiments we did theoretical calculations.All calculations in this work where carried out with the AM1 level of theory using the GAUSSIAN 03 suite of programs. 17More information about these methods is available elsewhere. 18,19able 1 summarizes our results.The table shows the thermodynamic parameters for the product (3) where T (temperature in K), S (entropy in J mol -1 K -1 ), C p (heat capacity at constant pressure in kJ mol -1 K -1 ), and ∆H=H° -H°2 98.15 (enthalpy content, in kJ mol -1 ), T 1 =100 K, T 2 =298.15K, and T 3 =1000 K calculated AM1 frequencies.The theoretical vibrational spectrum and structure are shown above.In the structure, all bond lengths are in angstroms (Å) and bond angles are in degrees (°) and the frequencies are in cm -1 , and the IR intensities in KM/mol (broadened by the Doppler method).These calculations are useful for future thermodynamic studies as well as for NIST database indexing.obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
General Procedures.A mixture of 6.3 g (105 mmoles) of ethylenediamine 1 and 21 g (210 mmoles) of acetylacetone 2 was stirred in absolute ethanol (100 ml) at room temperature.The mixture