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[structure: see text] A new transition state of the addition step in the Baeyer-Villiger reaction was found. The role of proton acceptor is played by the carbonyl oxygen atom, and the free energy barrier is 12.7 kcal/mol lower than that previously reported. This finding changes the mechanism for the acid catalysis and could be of interest for similar reactions in which it is known that such catalysis occurs, especially in nonpolar solvents.

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ABSTRACT: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 (R1) and pendant (R2) groups, where R1 = -CH 3 , -(CH 2 ) n -CH 3 (n = 2, 4, . . . , 16) and R2 = H, CH 3 , C 2 H 5 , C 3 H 7 , C 2 H 5 -OH, C 2 H 5 -NH 2 , C 2 H 5 -SH, C 2 H 5 -COOH, and C 2 H 5 -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. REACTIVITY PROPERTIES OF DERIVATIVES OF 2-IMIDAZOLINEFinally, 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.

The corrosion inhibitor properties of the 3-amino-1,2,4-triazole (ATR) and 2-aminothiazole (ATH) molecules were studied by means of polarization curves and electrochemical impedance spectroscopy techniques. The experimental results indicate that ATH is a bad or dangerous inhibitor at low concentrations while ATR behaves as an efficient inhibitor at all concentrations. The rationalization of this behavior was achieved by means of first principles theoretical calculations, of the all-electron type, performed with the Gaussian-98 program, at the HF, MP2, B3LYP, and BLYP levels of theory, in concert with 6-31G* * orbital basis sets. The reactivity of ATR and ATH was addressed in terms of the computed frontier molecular orbitals, highest occupied molecular orbital and lowest unoccupied molecular orbital, charge distributions, reactivity indices, and electrostatic potentials (EPs). These theoretical parameters indicate that the ATR moiety has much greater inhibitor efficiency than ATH, since, for instance the EP of the former displays two maximums on the nitrogen centers, favorable for the coordination with the metallic centers, while the latter has only one maximum. Analysis of the coordination modes of these two molecules with iron atoms indicates that in ATR-Fe, ATR is bonded to Fe through two nitrogen atoms of the ring yielding a highly stable ATR-Fe system. However, in ATH-Fe, ATH is bonded to Fe only through one N atom, because the S center experiences a repulsive effect with the metal atom. These experimental results suggest that derivatives based on the triazole rings are good candidates for the design of high performance corrosion inhibitors. © 2002 The Electrochemical Society. All rights reserved.