Jt-interaction

The polar interactions are often divided into weak, moderate and strong interactions that have been, somewhat arbitrarily, given terms such as jt/jt interactions,... 

According to Anh s theory, the cyclopentadienes having snbstitutents of second and third row elements such as SR and SeR at the 5-positions are expected to react with syn n facial selectivity since the stabilization dne to n-jt interaction in such systems is larger than 1. The observation contradicted the prediction [3,4,7]. We and Ohwada... 

Mataka and coworkers reported the studies of the Diels-Alder reactions of [3.3] orthoanthracenophanes 96 and 97, of which anthraceno unit, the potential diene, has two nonequivalent faces, inside and outside. The reactions of 96 with dien-ophiles gave the mixtures of inside and outside adducts with the ratios between 1 1 and 1 1.5. However, the ratio changes drastically, in favor of the inside adducts, when 97 reacts with dienophiles such as maleic anhydride, maleimide and naphto-quinone [55] (Scheme 46). Mataka suggested that the Jt-facial selectivity is controlled by an orbital interaction between the electron-poor dienophiles and the Jt-orbital of the facing aromatics, which would lead to a stabilization of the transition state, while Nishio suggested that the selectivity is due to the attractive k/k or CH/jt interaction [53]. 

Scheme 8 The orbital phase relationship of the continuity in the (Jt, interaction...

In anion-jt interactions with electron-deficient (neutral) aromatic tt-acceptors, the halide lies preferentially over the periphery of the aromatic ring (as illustrated in Fig. 13a) and this is apparently related to the shape of the acceptor LUMO (presented for comparison in Fig. 13b). 

Hydrogen bonding Jt-Jt interaction Dipole stacking Steric interaction... 

Coordination frameworks of pyridazino[4,5-ri]pyridazine have revealed a pronounced ability for anion Jt interactions <06CC4808>. 

In these molecules both experimental and theoretical results indicate that the a-jt interaction is practically non-existent. 

The mechanism for the hydrogenation probably involves Rh-jt interaction with the unsaturated systems. The selectivity of competitive hydrogenation experiments has established the relative order of the interaction forces [3] ... 

On the other hand, complexes with weak Jt interaction between the metal and the carbene will have an energetically low-lying K orbital. In addition to this, electron-transfer from the metal to C will be less efficient, thus leading to a more positively charged carbene fragment. Hence, carbene complexes with a large energy gap and poor orbital overlap between the metal d orbital and the carbene 2 p orbital will be prone to react with nucleophiles. 

Zacharias, N. and Dougherty, D.A. Cation-JT interactions in ligand recognition and catalysis. Trends Pharm. Sci. 2002, 23, 281-287. 

M. Nishio, M. Hirota and Y. Urezama, The CH/jt Interaction. Evidence, Nature, and Consequences, Wiley-VCH, New York, 1998. 

This selectivity was attributed to the perpendicular geometry of the vinylic hydrogen atom to the olefinic plane. In such a conformation, the vinylic hydrogen is activated considering the large a -jt interactions between the vinyl C—H bond and the reacting C=C double bond (Scheme 25). 

Cation-JT interactions have been primarily invoked as the major reason which dictates the site selectivity for the ene pathway. DFT calculations at the B3LYP/6-31G level of theory revealed that the binding site of Na+ to the substrates of Table 23 is controlled significantly by the presence of substituents capable of interacting with the cation via non-bonded electron pairs (e.g. fluorine or oxygen atoms). The Na+ -F interaction, for example, is highly exothermic and is the driving force for the facile adsorption of fluorinated compounds within Na-Y. ... 

Some of the materials highlighted in this review offer novel redox-active cavities, which are candidates for studies on chemistry within cavities, especially processes which involve molecular recognition by donor-acceptor ii-Jt interactions, or by electron transfer mechanisms, e.g. coordination of a lone pair to a metal center, or formation of radical cation/radical anion pairs by charge transfer. The attachment of redox-active dendrimers to electrode surfaces (by chemical bonding, physical deposition, or screen printing) to form modified electrodes should provide interesting novel electron relay systems. 

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