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T‐shaped arrangements in the homodimers A and C of benzene and hexafluorobenzene, respectively, are rationalized by polar effects, but face‐to‐face stacking dominates in the 1:1 heterodimer B. The dynamics of a series of fluorinated 1,8‐diarylnaphthalenes clearly demonstrate the dependence of arene–arene interactions on the electronic characteristics of the arenes. The results are important for the design of supramolecular structures.

Several 1,8-diarylnaphthalenes have been prepared, and the barrier to rotation around the arylhaphthalene bond has been measured. In these molecules steric congestion forces the aryls in a parallel stacked geometry. The barriers to rotation were used to evaluate the strength and to investigate the nature of the interaction between the arenes. The variance of the AG+ for the rotation upon arene substitution with electron donating or electron withdrawing groups indicates that polarh electrostatic effects dominate over charge-transfer effects in determining the arene/arene interaction.Non covalent interactions between aromatic units (1) play a major role in determining the properties and the behavior of molecules in a variety of processes, such as stereocontrol of organic reactions (2) and molecular recognition (3), and in affecting the structure of many biologically relevant molecules (4). In order to establish the influence exerted by arene/arene interactions on these phenomena and to learn how to use them in molecular design, we must understand the relative importance of the factors contributing to the interaction.The energy of the interaction between two arene units divides roughly into a polar (electrostatic and induction) and a van der Waals term (dispersion) (1). The polar term depends on the relative charge distribution and on the interaction between the charge of one arene with the induced change in the charge of the other. The van der Waals term depends on the contact surface area. Since in the case of two interacting benzenes the surface area is relatively small, the polar term should dominate the interaction (1).The charge distribution in benzene can be described as an electron rich central core surrounded by an electron poor perifery (5). This description is in agreement with the preference shown by crystalline (6), liquid (7), and gaseous benzene (8) for the edge-to-face, T-shaped geometry, and predicts an unfavorable repulsive interaction for the face-to-face stacked disposition, and a favorable attractive one for the offset stacked arrangement. On this basis, the interaction between two parallel stacked benzenes can be studied only in those systems in which this geometry is imposed by steric factors.We reasoned that the steric congestion at the peri positions of naphthalene should indeed force two phenyl rings in the required orientation (9). This orientation is lost when a phenyl group rotates around the phenylhaphthalene bond (10,ll). Thus, the barrier to rotation should depend on the strength of the parallel stacked interaction. and. in a homologous series of comnounds. the variance of the hamer unon substitution of the aryls with electon donating (EDG) and electron withdrawing (EWG) groups should provide a new insight into the nature of the R/R interaction.

This review article is divided in two parts. In the first part (Sections 2 and 3) selected examples of the publications that appeared in the literature in the period 2003–2005 in the field of immobilized organic catalysis are presented. When appropriate, the results of these publications are compared to those reported earlier and already discussed in a previous review article (see ref. 4). On the basis of this survey, in Section 4 some general considerations about when and why a supported version of an organic catalyst is worth developing are proposed. In Section 4 a list of suggestions about how the process of immobilization should be carried out is also included, taking into account several factors such as the properties of the catalyst, the nature of the support, and the mode of connection of the catalyst to the support.

Two series of conformationally restricted polycyclic compounds (1-3 and 4-7) have been synthesized as model systems for studying the through-space interactions between face-to-face, center-to-edge (parallel-offset) oriented arenes. These compounds feature different X substituents on one of the interacting rings. By monitoring the variation of the delta Gz for the rotation around the aryl-aryl bond in 1-7 as a function of X by 2D [1H,1H] EXSY NMR spectroscopy, it was found that the barriers increase on passing from electron-donating to electron-withdrawing substituted derivatives. Quantum mechanical calculations [MP2/DVZ (2d,p)//B3LYP/DVZ(2d,p)] gave barrier values and variations in agreement with the experimental data. The results are consistent with a repulsive arene-arene interaction dominated by electrostatic effects.

A model for studying polar-pi interactions between arenes spaced at van der Waals distances is developed on the basis of peri-diarylbiphenylenes. A set of 1,8-diarylbiphenylenes is synthesized comprising two Hammett series, one with reference to mesityl ring interactions and the other with reference to pentafluorophenyl ring interactions. X-Ray crystal structures of several derivatives are determined. Barriers to rotation of the probe aryl ring are derived from dynamic NMR data and show a trend for the mesityl reference series (DeltaG(not equal) vs. sigma(0)). The model is also used as a test for comparison of modern density functional methods, including B3LYP, M06-2X and BMK functionals; dispersive effects are seen to be an important factor in the proper theoretical treatment of arene interactions.

Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without the Numbering of fullerenes (IUPAC Recommendations 2005)Abstract: Rules for numbering (C 60 -I h ) [5,6]fullerene and (C 70 -D 5h(6) ) [5,6]fullerene were codified in a publication "Nomenclature for the (C 60 -I h ) [5,6] and (C 70 -D 5h(6) ) [5,6]fullerenes" published in Pure Appl. Chem. 74 (4), 629-695 (2002). The current publication contains recommendations for numbering a wide variety of fullerenes of different sizes, with rings of different sizes, from C 20 to C 120 , and of various point group symmetries, including low symmetries such as C s , C i , and C 1 , as well as many fullerenes that have been isolated and well characterized as pristine carbon allotropes or as derivatives. These recommendations are based on the principles established in the earlier publication and aim at the identification of a well-defined and preferably contiguous helical pathway for numbering. Rules for systematically completing the numbering of fullerene structures for which a contiguous numbering pathway becomes discontiguous are presented.

Two chiral bisoxazolines (box) supported on a modified poly(ethylene glycol) (PEG) have been prepared by a reaction sequence that involved formation of the properly functionalized box and their attachment to the polymer matrix by means of a spacer and a linker. The solubility properties of PEG allowed use of the supported box as ligands in some catalytic asymmetric transformations carried out under homogeneous conditions and to recover the ligands as if bound to an insoluble support. When the supported box were employed in combination with Cu(II) salts in the Diels-Alder cycloaddition between cyclopentadiene and N-acryloyloxazolidinone, low levels of enantioselectivity were observed (up to 45% ee). Much better results were obtained in the cyclopropanation of styrenes carried out in the presence of CuOTf (up to 93% ee) and in the ene-reaction between alpha-methylstyrene or methylenecyclohexane and ethylglyoxalate (up to 95% ee). One of the ligands, readily recovered by precipitation and filtration, was recycled two times in the ene-reaction with marginal loss in the catalytic activity and very limited erosion of the enantioselectivity.