Reactivity properties of derivatives of 2-imidazoline:: An ab initio DFT study

The structural and electronic properties of a series of imidazoline (I) derivatives R1-I-R2 have been studied by means of density functional theory. The chosen compounds have different chain lengths (RI) and pendant (R2) groups, where R1 = -CH3, -(CH2)(n)-CH3 (n = 2,4,...,16) and R2 = H, CH3, C2H5, C3H7, C2H5-OH, C2H5-NH2, C2H5-SH, C2H5-COOH, and C2H5-Cl. All-electron calculations were carried out by means of the Gaussian-98 program. Natural and Mulliken population analysis were determined for each of the neutral and charged molecules. The reactivity was analyzed in terms of the Fukui indices. The results indicate a high reactivity for both the tertiary (showing the biggest) and the iminic nitrogen atoms of the imidazoline ring. Although the N site of the pending groups has a much lower reactivity, this is significantly increased when a sulfur atom replaces it. In general, the reactivity of the N atoms of the ring depends significantly on the substituents. As expected, the frontier molecular orbitals, highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), also describe the reactivity behavior. As the size of the R1 chain increases, the two N atoms of the ring increase their nucleophilic character, since the HOMOs become more highly located. The obtained results help to explain the observed increased activity of these derivatives when they are used as inhibitors of corrosion moieties on metallic surfaces. Finally, the solvent effects on the ground-state geometry were studied for one of the most promising reactive imidazolines; for which its interaction with an iron oxide surface was also addressed. (C) 2001 John Wiley & Sons, Inc.