Intramolecular acid-base interaction

The intramolecular Lewis acid-base interaction of type B is of course always in competition with an intermolecular interaction, as indicated by formula C. Again, a bulky group in a-position to X can favor the formation of monomer B. 

Before studying some examples more closely, let us consider some cases which are not listed in Table 13. There are numerous compounds SnX2 which are definitely monomeric but are nevertheless no carbene analogs since their valence electron number at the tin atom is at least eight. These compounds contain chelating ligands which can stabilize the carbenoid tin atom due to intramolecular Lewis acid-base interactions as shown by structure A and B (see also Chapter 3). 

Substitution of the dimethylsilyl group by bis(tert-butyl)-stannyl does not change the structure in solution, e.g. 33 is found to be monomeric. A very interesting dimer is 26. In contrast to the centrosymmetrical dimer of 1 (C-Symmetry), 26 has a twofold axis (C2, see Fig. 9). This special structure may be due to intramolecular Lewis acid-base interactions between the boron and nitrogen atoms 39). Nevertheless,... 

One additional application of the E and C equation will be discussed in this section. In many acids or bases, there is a constant contribution to the energy that accompanies all acid-base interactions. For example, in methylcobaloxime, the dimer must be broken in a basic non-polar solvent e.g., benzene) a given acid (e.g., phenol) bonds to the solvent in hexafluoroisopropanol, there is intramolecular hydrogen bonding and in any series of displacement reactions, a constant base could be... 

Metal ion catalysis of salicyl phosphate hydrolysis is much more complicated than that of Sarin, since the former substrate can combine with metal ions to give stable complexes, and some of the complexes formed do not constitute pathways for the reaction. In addition the substrate undergoes intramolecular acid-base-catalyzed hydrolysis which is dependent on pH because of its conversion to a succession of ionic species having different reaction rates. Therefore a careful and detailed equilibrium study of proton and metal ion interactions of salicyl phosphate would be required before any mechanistic considerations of the kinetic behavior in the absence and presence of metal ions can be undertaken. 

The presence of the l,ll-diamino-6-oxoundecane in hydrolysates of heat-treated nylon-6 [359] thus is obviously the result of the hydrolysis of the Schiff base moiety. The absence of the corresponding oxo-structure in the hydrolysates of gelled nylon-6,6 may be indicative of an analogous decarboxylation mechanism entailing intramolecular acid amide interaction Hydrolysis of the Schiff base structure yields, as indicated, hexamethylene diamine and cyclopentanone, both of which have been found. 

The favorability of acid-base reactions is affected, in pa by electrostatic interactions between charged atoms a dipoles within the same molecule. The equilibrium w shift in the direction of an ion that is stabilized 1 intramolecular ion-dipole interactions. 

One of the most prominent hydrogen-bonded systems is DNA. Despite numerous experimental and theoretical investigations on vibrational spectra of nucleic acid bases [7-13], information on inter- and intramolecular interactions in base pairs and DNA oligomers is still limited [14-25]. A recent example is the work on single adenine-uracil (AU) base pairs in the Watson-Crick geometry in solution, which showed an enhancement of vibrational energy... 

FIGURE 13. Molecular structure of the chloro(alkyl)stannylene 61a (left) and of chloro(alkyl)plum-bylene 62b (right) in the crystal, both forming asymmetric halogen-bridged dimers due to competitive intramolecular Lewis acid/Lewis base interactions. These are depicted as dashed lines (----) and the longer E—Cl bonds as thin solid lines... 

The silatrane molecules with their intramolecular Si N Lewis acid/base bond have already been listed together with other nitrogen compounds (Table 4). For 1,4-bis(trimethylsiloxy)benzene, a crystal structure analysis proves a 60° dihedral angle for the conrotatory twist of the RsSiO substituents around the OC6H4O axis, reducing the ng/jr interaction to 9.24 — 7.96 = 1.28 eV (cf. Figure 15). 

Solvatochromism and specific features of interaction between nitropyrazoles and amphiprotic solvents have been studied in detail by Prof. Turchaninov s team [1119-1123, 1127]. The dependence on acid-base properties of solvents of the electron transition in 4-nitropyrazole connected with intramolecular charge transfer has been analyzed [1121], Amphiprotic solvents with a pronounced acidic function form with 4-nitropyrazole cyclic solvates. The results of ab initio calculations 6-31G show that a cyclic complex of both 4-nitropyrazole and 3-nitropyrazole with one water molecule is thermodynamically more stable than a linear complex of the same composition by 0.38 and 1.0 kcal/mol, accordingly [1120-1123] ... 

The formation and stoichiometry of the polymer complex between nucleic acid analogs are affected by two important factors. The first is the base-base distance in the polymer chain, represented as xA and yA in Fig. 17. This distance is one factor in intramolecular base-base interactions in the polymer chain, which also influences what can be called the penetration ability of the polymer. 

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