Intermolecular stabilization

Difluoroaminofluorodiazirine (225) extrudes nitrogen at only 75 °C. Intramolecular stabilization gives trifluoromethylenimine (226) added tetrafluoroethylene is cyclopropa-nated. This type of dichotomy is not often found in carbene chemistry alkylcarbenes undergo intramolecular stabilization as a rule, whereas intermolecular stabilization is observed exclusively with alkoxycarbonylcarbenes and with difluorocarbene. In the latter case CF2 attacks its precursor when no other reaction partner is present. 

Besides such intermolecular stabilized compounds, intramolecular stabilized compounds have also been reported. Rettig et al. described the synthesis of phosphine-stabilized Al—N monomers by using a tripodal ligand [101]. More recently, Raston et al. reported on the synthesis of compounds of the type [H2A1E(H)R]2, containing only weak Al—H bridges [102]. 

Rabin, O. Vigalok, A. Milstein, D. A novel approach towards intermolecular stabilization of para-quinone methides. First complexation of the elusive, simplest quinone methide, 4-methylene-2,5-cyclohexadien-l-one. Chem. Eur. J. 2000, 6, 454-462. 

As was the case for dinitrobenzene, the meta and para nitroaniline isomers have essentially the same gaseous enthalpy of formation. In the gaseous phase, it is surprising to find that despite the more attractive quinonoid resonance structures92 for the para isomer (58) than for the meta (59) the met a and para nitroaniline have essentially the same gas-phase enthalpy of formation. In the solid and liquid states the intermolecular stabilization lowers the enthalpy of formation of the para isomer relative to the meta. Interestingly, the gas-phase intramolecularly hydrogen-bonded ortho isomer is of comparable stability to its isomers. In contrast, it is considerably less stable than its isomers in the solid state because it can form fewer intermolecular hydrogen bonds. All isomers of nitroaniline are more stable than calculated by additivity. 

Two further mechanisms are known to trap electronic charge in thin films intermolecular and resonance stabilization. In resonance stabilization, electron attachment to a molecular center produces an anion in a vibrationally excited state that is then de-excited by energy exchange with neighboring molecules. When the initial anion ground state lies below the band edge or lowest conduction level of the dielectric, then the additional electron may become permanently trapped at the molecular site. In this case, a permanent anion is formed (e.g., the case of O2 [220]). Intermolecular stabilization refers... 

Razskazovskii Y, Colson A-O, Sevilla MD (1995) Nature of thiyl radical ESRand ab initio MO evidence for intermolecular stabilization of the charge transfer state, RS+00. J Phys Chem 99 7993-8001... 

However, in order to predict the occurrence of proton transfer for a general case one cannot restrict themselves in their analysis to the deprotonation energy of proton donor (HA). The occurrence of intermolecular proton transfer results from a subtle interplay between the deprotonation energy of HA, protonation energy of nucleobase (NB), and the intermolecular stabilization energy. A small variation in any of these parameters can alter the NB HA -o- NBH A equilibrium. For the proton transfer to occur, the stabilizing interaction in the NBH - A system needs to (i) compensate the barriers of hypothetical process ... 

Intermolecular Stabilized l-Chromium-2-sila-l,3-diene Complexes... 

Several additional examples of intermolecular stabilization have been reported. Fez has prepared Ba(hfac)2(18-crown-6) and Gleizes has obtained the structure of Ba(tmhd)2(MeOH)2. The isolation of Ba(tmhd)2(TMEDA)2 (Figure 11) has been achieved as well, although the vapor-phase composition of this species was not determined. ... 

Intra- and intermolecularly stabilized iminosilanes are obtained by using heteroaromatic substituted aminofluorosilanes. For example, the bicyclic system 3 is obtained in an insertion reaction of the iminosilane into a polar C-H bond of the pyrrole substituent. Using smaller substituents the [2+2] cycloaddition product 4 is obtained [6]. 

A similar intermolecular stabilization has also been observed in (r-Bu)2Ga(OCPha) wherein the carbon atom of one of the phenyl rings approaches the gallium center offering... 

There is a third geometrical type, in which parallel aromatic molecules are parallel but not offset, i.e., face-to-face (FF) or eclipsed. For the electrostatic reasons just outlined, this is not an energy minimum for a pair of identical molecules in a symmetrical motif and is rarely observed. However, if the two aromatic molecules in a motif are different, with complementary electron distributions, the FF motif can be the energy minimum. One of the better-known instances of this is the intermolecular interaction between a hydrous arene and a perfluorous arene. Due to the opposite polarization of the C-H and C-F bonds, the molecular quadrupoles of CgHe and CgFe are oppositely signed, and so the electrostatic intermolecular stabilization between them is maximized with FF geometry. 

These data can be explained in terms of the high stabilization energy resulting from solvation of the excited t state. High p values in these cases indicate that the polar solvent-solute intermolecular stabilization ofthe zwitterionic excited t state is very sensitive to intramolecular substituent effects. In contrast, there is no dependence of Stokes shifts on a-constants in cyclohexane, which is nonpolar aprotic solvent, where the vibrational relaxation ofthe Franck-Condon state plays a primary role in stabilizing the excited state. This implies that the vibrational relaxation is not sensitive to intramolecular donor-acceptor interactions. The observations showed that the ultrafast intra- and intermolecular electronic polarization plays a major role in determining the position of the Franck-Condon zwitterionic state and its sensitivity to the relaxation of polar-substituted stilbenes. 

Internal templating refers to the self-selection of library members through intramolecular or intermolecular stabilizing noncovalent interactions. Intramolecular self-templating is observed when the species formed in a DCL are capable of folding upon themselves (Figure 1.2c). The library members that are best able to form favorable noncovalent interactions within themselves will be ampHfied in the library. DCC has therefore been used to study the folding of peptides, nucleotides, and synthetic polymers (Chapter 6). It can be used to direct the reversible... 

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