We describe herein the first synthesis of a new class of anti-aromatic planar cyclooctatetraenes: the azatrioxa[8]circulenes. This was achieved by treating a suitably functionalised 3,6-dihydroxycarbazole with 1,4-benzoquinones or a 1,4-naphthoquinone. We fully characterised the azatrioxa[8]circulenes by using optical, electrochemical and computational techniques as well as by single-crystal X-ray crystallography. The results of a computational study (NICS) suggest that the central planar cyclooctatetraene is anti-aromatic when the molecules are in neutral or oxidised states (2+), and that the corresponding dianions are aromatic. We discuss the aromatic/anti-aromatic nature of the planar cyclooctatetraenes and compare them with the isoelectronic tetraoxa[8]circulenes.
Reaction of carbonyl compounds bearing electron-withdrawing substituents with non-activated aromatic hydrocarbons proceeds selectively in trifluoromethanesulfonic acid (TFSA) at room temperature to give linear, high-molecular-weight polymers.
The electronic structure of small (∼1 nm) silicon nanocrystals passivated with nitrogen and chlorine is explored using density funcional theory calculations. The HOMO-LUMO gap of 3.2 and 3.3 eV, calculated for the fully nitrogen [Si 35 (NH 2 ) 36 ] and chlorine passivated (Si 35 Cl 36 ) nanocrystals, respectively, correlate quite well with experimental observations describing the blue and/or white photoluminescence and electroluminescence of silicon nanocrystals, embedded in chlorinated silicon nitride films. On the other hand, the ionization energy and the electron affinity allow us to study the electron transfer properties of these systems. The chargetransfer capacity of these nanocrystals is modified in opposite directions with respect to hydrogen-passivated nanocrystals, becoming good electron acceptors with Cl passivation and good electron donors with NH 2 passivation.
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.
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