Vibronic coupling in electronic transitions with significant Duschinsky effect

Conceptual and mathematical difficulties arise in the study of transitions between vibronic states belonging to crossing Born-Oppenheimer hypersurfaces with significantly different positions and shapes of the minimum-energy nuclear configurations (Duschinsky effect). This article presents an analytic procedure for the evaluation of the pertinent coupling integrals, adopting a normal coordinate reference system for the internal nuclear motion and harmonic approximation. The Duschinsky effect is properly considered. The procedure was applied to the dynamics of electron transfer in neutral mixed valence monoradicals, using the diabatic representation. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 233–244, 1997     

Rearrangement of N-Aryl-2-Vinylaziridines to Benzoazepines and Dihydropyrroles: A Synthetic and Theoretical Study

Herein we report the one-pot synthesis of several N-heterocyclic compounds by rearrangement reactions of N-aryl-2-vinylaziridines. The optimization of the synthetic methodology employed allowed us to obtain differently substituted 2,5-dihydro-1H-benzo[b]azepines in good yields and purities. The relationship between the nature of the starting N-aryl-2-vinylaziridine and the obtained N-heterocycle was also investigated. Finally, to rationalize all the experimental results reported in this paper a theoretical study was performed that casts light on the reaction mechanism.     

Binding and redox properties of iron(II) bonded to an oxo surface modeled by calix[4]arene

The syntheses of the parent compounds [(p-Bu(t)-calix[4]-(O)2(OR)2)Fe-L] [R = Me, L = THF, 5; R = Bu(n), L = THF, 6; R = PhCH2, L = THF, 7; R = SiMe3, L = none, 8] have been performed by reacting the protonated form of the dialkylcalix[4]arene with [Fe2Mes4] [Mes = 2,4,6-Me3C6H2]. All of them undergo one-electron oxidative functionalization. By use of different oxidizing agents, the following iron(III) derivatives have been obtained: [(p-Bu(t)-calix[4]-(O)2(OR)2)Fe-X] [X = Cl, R = Me, 9; X = I, R = Me, 10] and [(p-Bu(t)-calix[4]-(O)2(OR)2)2Fe2(mu-X] [X = O, R = Me, 11; X = O, R = Bu(n), 12; X = S, R = Me, 13], 9 and 10 being particularly appropriate for a further functionalization of the metal. The last three display typical antiferromagnetic behavior [J = -78.6 cm-1, 11; J = -64.1 cm-1, 13]. In the case of 7 and 8, the reaction with O2 led to the dealkylation of one of the alkoxo groups, with the formation of a dimeric iron(III) derivative ([mu-p-Bu(t)-calix[4]-(O)3(OR))2Fe2] [R = PhCH2, 14; R = SiMe3, 15] [J = -9.8 cm-1]. The reaction of the parent compounds with ButNC and diazoalkanes led to the formation of [Fe=C] functionalities supported by a calix[4]arene oxo surface. The following compounds have been isolated and characterized: ([p-Bu(t)-calix[4]-(O)2(OR)2)Fe=CNBut] [R = SiMe3, 16, nu CN = 2175 cm-1], ([p-Bu(t)-calix[4]-(O)2(OR)2)Fe=CPh2] [R = Me, 17; R = PhCH2, 18; R = SiMe3, 19]. The three carbene complexes 17-19 display quite an unusual high-spin state, which is a consequence of the formation of a weak pi interaction between the metal and the carbene carbon, as confirmed by the extended Hückel calculations. The carbene functionality has been removed from the iron center in the reaction with O2 and HCl. The proposed structures have been supported by X-ray analyses of complexes 8, 9, 12, 14, 16, 17, and 19.     

Quasi-one-dimensional systems and localized defects: Some results of the Green's matrix formalism

The application of the self-consistent field (SCF ) local-impurity formalism to quasi-one-dimensional systems is discussed. We describe a general procedure for an accurate numerical determination of the Green's function matrix elements of the unperturbed system. An application to a local impurity in a model chain with two orbitals per unit cell is reported. The changes in the charge-bond-order matrix and in local and total density of states due to the impurity are discussed with special emphasis on the changes at the critical points (van Hove singularities) at the band edges. The Green's matrix approach is used to reexamine long-range Friedel oscillations caused by an impurity in a strictly one-dimensional metal. The extent of the long-range tail of the perturbed charge density is in an inverse relation to the localization length of the impurity state: the stronger the perturbation the more localized is the bound state and the more extended are the oscillations in the charge distribution. The results for the model chain with two orbitals per unit cell indicate that the impurity-induced change in charge distribution may be locally screened by redistribution of the population of the on-site orbitals, therefore damping possible oscillations and leading to a faster decay than in strictly one-dimensional systems.     

Diffusion coefficients of metals in inert gases: Comparison of calculations with experimental data

In the present work some simple methods of calculation of the diffusion coefficient by using the model and experimental interaction potentials are discussed. An applicability of such calculations for diffusion of metals in inert gases is analyzed.     

Ein einfacher Zugang zu 4-hydroxy-2,5-dimethyl-3(2H)-furanon (furaneol), einem Aromabestandteil von Ananas und Erdbeere

Furaneol®

1 Registered trade mark of Firmenich SA.

[4-hydroxy-2,5-dimethyl-3(2H)-furanone ( 1 )], a flavour component of pineapple and strawberry, has been prepared by a two-step synthesis starting with readily available 3-hexyne-2,5-diol. By the same method 4-hydroxy-5-methyl-3(2H)-furanone ( 2 ) and 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone ( 3a ) have been prepared from 2-pentyne-1,4-diol and 3-heptyne-2,5-diol, respectively.     

A structural and theoretical analysis of transition metalloporphodimethenes and their relationship with metalloporphyrins

The paper reports the synthesis of the first-row transition metal hexaethylporphodimethene derivatives [(Et6N4)M] [M=Mn, 3; M=Co, 5; M = Cu, 7] on a multigram scale, which makes them easily available for reactivity studies. After synthesis they were converted into the corresponding five-coordinate [(Et6,N4)M(L)] [M = Mn, L =THF, 8; M =Co, L = Py, 9] and six-coordinate [(Et6,N4)M(L)2] [M = Mn, L = THF, 10; M = Mn, L = Py, 11] derivatives. The compounds mentioned above and those recently reported, namely the iron and nickel derivatives 4, 6, 12, and 13, permit the presentation of the first coherent report on the structural, optical, magnetic, and electronic characteristics of the first-row transition metal porphodimethene derivatives. The experimental results, coupled with a detailed theoretical analysis (Density Functional Theory, DFT), give the appropriate background for future development of the porphodimethene skeleton, which paves the way from porphyrinogen to porphyrins. In addition, this report, encompassing the entire first row of transition metal ion porphodimethenes, allows a valuable comparison to be made with the corresponding metallated porphyrins, thus establishing the peculiar differences in terms of structural and electronic properties and potential reactivity.