Ions, dipolar

Ozonation ofAlkenes. The most common ozone reaction involves the cleavage of olefinic carbon—carbon double bonds. Electrophilic attack by ozone on carbon—carbon double bonds is concerted and stereospecific (54). The modified three-step Criegee mechanism involves a 1,3-dipolar cycloaddition of ozone to an olefinic double bond via a transitory TT-complex (3) to form an initial unstable ozonide, a 1,2,3-trioxolane or molozonide (4), where R is hydrogen or alkyl. The molozonide rearranges via a 1,3-cycloreversion to a carbonyl fragment (5) and a peroxidic dipolar ion or zwitterion (6). 

The dipolar ion (6) and its alternative resonance form R2C=0" —O , exist in both sjn- and i //-configurations that are formed in different amounts. 

The dipolar ion can react in several ways according to the solvent and the stmcture of the olefin. In inert solvents, if the carbonyl compound is highly reactive (eg, an aldehyde), the dipolar ion can be added to the carbonyl fragment to give the normal ozonide or 1,2,4-trioxolane (7) for example, 1,1-and 1,2-dialkylethylenes react in this manner. Tri- or tetraalkyl-substituted olefins produce a smaH, if any, yield of an ozonide when the ozonolysis is... 

The zwitterion is also often referred to as a dipolar ion. Note, however, that it is not an ion, but a neutral molecule. 

We saw in Sections 20.3 and 24.5 that a carboxyl group is deprotonated and exists as the carboxylate anion at a physiological pH of 7.3, while an amino group is protonated and exists as the ammonium cation. Thus, amino acids exist in aqueous solution primarily in the form of a dipolar ion, or zwitterion (German zwitter, meaning "hybrid"). 

Cohn, E. J., and Edsall, J. T., Proteins, Amino Acids, and Peptides as Ions and Dipolar Ions, ... 

Interaction between Crosslinked Polyelectrolytes and Dipolar Ions... 

High sorption capacities with respect to protein macromolecules are observed when highly permeable macro- and heteroreticular polyelectrolytes (biosorbents) are used. In buffer solutions a typical picture of interaction between ions with opposite charges fixed on CP and counterions in solution is observed. As shown in Fig. 13, in the acid range proteins are not bonded by carboxylic CP because the ionization of their ionogenic groups is suppressed. The amount of bound protein decreases at high pH values of the solution because dipolar ions proteins are transformed into polyanions and electrostatic repulsion is operative. The sorption maximum is either near the isoelectric point of the protein or depends on the ratio of the pi of the protein to the pKa=0 5 of the carboxylic polyelectrolyte [63]. It should be noted that this picture may be profoundly affected by the mechanism of interaction between CP and dipolar ions similar to that describedby Eq. (3.7). 

One of the most rational means for displacing a broad zone is electrolyte desorption under the conditions of decreasing degree of ionization, i.e., when counterions are converted into dipolar ions, uncharged molecules and coions. This conversion corresponds to a sharp decrease in distribution coefficients of the desorbed substance. Hence, the displacement of equilibrium parame ters at a high rate of mass-exchange is one of the methods of selective stepwise chromatography. 

The energy available from the anthracene triplet (42 kcal/mole) is sufficient to produce either of these states. The singlet excited molecule subsequently attacks a ground state anthracene to produce the observed endoperoxide. The 1Aff state is believed to be responsible for the addition to anthracene to form the endoperoxide since it closely resembles a diradical species, while the 1Ss+ state more closely resembles a dipolar ion. 

Benzylideneeyclopropane (156) and diphenylmethylenecyclopropane (157) reacted rapidly with TCNE to afford 159 and 160, respectively, in good yields. Since the reaction rate is highly dependent on the solvent polarity, the cycloadditions of 156 and 157 with TCNE were rationalized as stepwise reactions involving the dipolar ions 158 (Scheme 23) [37],... 

No similar meta substituent effect exists for ions since resonance between a singlet and triplet (diradical) state is prohibited. The dipolar ion theory would suggest that suitably disubstituted radicals should be especially stable, particularly in polar solvents, because of structures like III. 

Dipolar ion, reaction with solvents, 17 782 Dipolar polarization, 10 21 Dipole-dipole interactions, 15 103 23 91-92 in water, 26 16... 

It seems probable that these reactions proceed by nucleophilic attack of the phosphorus atom on the carbonyl group or activated olefin with the formation of a dipolar ion intermediate, which rearranges to a phosphazene by migration of a hydrogen atom or silyl group. 

For glycine, it is known that the dielectric constants of water increases rapidly and linearly with the concentration of the amino acid, reaching a value of about 135 at a concentration of 2.5 mol liter" at 25 C. D is given by D = 78.54 + 22.58C, where 78.54 is the measured value of D for pure water, 22.58 is the numerical value of the dielectric increment, and C is the concentration in mol/liter. This great increase of D reflects the extremely large moment of glycine as a dipolar ion, and the linearity of the relationship represents the proportionality between D and polarizability that is characteristic of strongly polar media. 

Equation (24) renders intelligible the behavior of the dielectric constant of dipolar ions in polar solutions. It explains the linear increase of D with concentration, since changes in partial molar volumes, only slightly dependent on concentration, can only affect the DyVi term. It also explains the nearly identical values of D of the amino acids of the same moment, and the fact that D of a given amino acid is insensitive to changes in the dielectric constant of the solvent, for the change of solvent can directly affect 8 only through the term D V2. 

Zaigmondygold number chem The number of milligrams of protective colloid necessary to prevent 10 milliliters of gold sol from coagulating when 0.5 milliliter of 10% sodium chloride solution is added. zig-mon-de gold, n3m-b3r zwitterion See dipolar ion. tsfid-3r,T,an ... 

Keefer, R.M. Interaction of ions and dipolar ions. IV. The solubility of cupric iodate in glycine and in alanine solutions, J. Am. Chem. Soc., 70(2) 476-479, 1948. 

Therefore, we can deduce that a-amino acids in solution at pH 7.0 exist as dipolar ions these are called zwitterions (German zwitter = hybrid) (see Section 13.1). 

The isoelectric point for lysine is that pH at which the compound is in an electrically neutral form, and this will be the average of pATa2 (the cation) and pAfa3 (the dipolar ion). For lysine, pATa2 = 8.95 and pATa3 = 10.52, so pi = 9.74. 

A zwitterion must not be confused with an ylide, which has opposite electric charges residing on adjacent atoms. The term dipolar ion, while often used in place of zwitterion, is not considered by lUPAC to be an acceptable synonym, and should be avoided. 

When proteins undergo hydrolysis, you wind up with 22 a amino acids, 20 of which are regulcir amino acids and 2 of which are derived amino acids. Amino acids are amphoteric (they possess the characteristics of both acids and bases and can react as either) because both acidic and basic groups are present. An internal acid-base reaction produces a dipolar ion known as a zwitterion (you can see the general structure of one in Figure 16-33). 

Methylation of dipolar ions 68 occurs exclusively at sulfur to yield, e.g., Ij 6i.62. N-analogs 71 give a mixture of products from methylation at both the exo- and the endocyclic nitrogen atoms. ... 

A mixture of phthalide and o-(hydroxymethyl)benzoic acid is formed from 159 and 1 M sodium hydroxide. The dipolar ion 111 is cleaved to 160 by... 

Dipolar ions like CN and OH can be incorporated into solids like NaCl and KCl. Several small dopant ions like Cu and Li ions get stabilized in off-centre positions (slightly away from the lattice positions) in host lattices like KCl, giving rise to dipoles. These dipoles, which are present in the field of the crystal potential, are both polarizable and orientable in an external field, hence the name paraelectric impurities. Molecular ions like SJ, SeJ, Nf and O J can also be incorporated into alkali halides. Their optical spectra and relaxation behaviour are of diagnostic value in studying the host lattices. These impurities are characterized by an electric dipole vector and an elastic dipole tensor. The dipole moments and the orientation direction of a variety of paraelectric impurities have been studied in recent years. The reorientation movements may be classical or involve quantum-mechanical tunnelling. 

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