1,4-dications

The relative sizes ofthe poten tial barriers in dicate that the AF force con Stan t is larger th an the V con stan t. fh e ph ase sh ift is 180 degrees for th e Fourier compoiien t with a two-fold barrier. Minima occur at 180, 0, and I 80 degrees and maxima at 90 and 90... 

Whereas the proton (H ) can be considered the ultimate Bronsted acid (having no electron), the helium dication (He ) is an even stronger, doubly electron-deficient eleetron aceeptor. In a theoretical, calculational study we found that the helionitronium trication (NOaHe" ) has a minimum structure isoelectronic and isostructural... 

Tests with animals have revealed that dioxin is one of the most toxic substances known Toward mice it IS about 2000 times more toxic than strychnine and about 150 000 times more toxic than sodium cyanide Fortunately however available evidence in dicates that humans are far more resistant to dioxin than are test animals and so far there have been no human fatalities directly attributable to dioxin The most prominent short term symptom seen so far has been a severe skin disorder known as chloracne Yet to be determined is the answer to the question of... 

Reactions with Parting of Radicals. The one-electron oxidation of cationic dyes yields a corresponding radical dication. The stabihty of the radicals depends on the molecular stmcture and concentration of the radical particles. They are susceptible to radical—radical dimerization at unsubstituted, even-membered methine carbon atoms (77) (Fig. 6). 

According to the electron-transfer mechanism of spectral sensitization (92,93), the transfer of an electron from the excited sensitizer molecule to the silver haHde and the injection of photoelectrons into the conduction band ate the primary processes. Thus, the lowest vacant level of the sensitizer dye is situated higher than the bottom of the conduction band. The regeneration of the sensitizer is possible by reactions of the positive hole to form radical dications (94). If the highest filled level of the dye is situated below the top of the valence band, desensitization occurs because of hole production. 

Substituents on the methine chain can stabilize the dye radical cation if the substituent (like methyl) is located on the high electron density carbons. However, no significant stabilization occurs when alkyl groups are on the alternate positions (like 9, 11 for the dication in Fig. 9). Current results for several dyes including die arbo cyanines and carbocyanines indicate that electronic stabilization of the dication radical lengthens the radical lifetime and also enhances the reversibiUty of the dimerization process (37). 

Dithiin, tetraphenyl-dication salt, 3, 968 half-wave potential, 3, 968 synthesis, 3, 982... 

Thianthrene, 2,3,7,8-tetramethoxy-dication, 3, 968 Thianthrenedicarboxylic acids applications, 3, 993 Thianthrene-2,6-dicarboxylic acids... 

An allowed alternative to the -ylium suffixes is citing the term cation (or dication , etc.) after the name of the corresponding radical. 

When substances ionise their neutral species produce positive and negative species. The ionisation constants are those constant values (equilibrium constants) for the equilibria between the charged species and the neutral species, or species with a larger number of charges (e.g. between mono and dications), l ese ionisation constants are given as pK values where pK = -log K and K is the dissociation constant for the equilibrium between the species [Albert and Serjeant The Determination of Ionisation Constants, A Laboratory Manual, 3rd Edition, Chapman Hall, New York, London, 1984, ISBN 0412242907]. 

Quinazoline [253-82-7] M 130.2, m 48.0-48.5 , b 120-121 /17-18mm, pK, -4.51 (aq H2SO4, anhydrous dication), pK 2.01 (anhydrous monocation), pK3 4.3 (equilibrium with 3,4-hydrated species), PK4 12.1 (hydrated anion). Purified by passage through an activated alumina column in benzene or pet ether (b 40-60°). Distd under reduced pressure, sublimed under vacuum and crystd from pet ether. [Armarego 7 Chem 1170 1961.]... 

Several doubly eharged ions are ineluded in Seheme 9.1 some have been observed experimentally. Ionization of 3,4-diehloro-l,2,3,4-tetramethyleyclobutene in Sbp5-S02 at —75 C results in an NMR spectrum attributed to the tetramethyl derivative of the cyclobutadienyl dication ... 

A dication derived from 1,3,5,7-tetramethylcyclooctatetraene is formed at —78 C in SO2CI by reaction with SbFj. Both the proton and carbon NMR spectra indicate that the ion is a symmetrical, diamagnetic species, and the chemical shifts are consistent with an... 

Alder and Sessions have reported that reductive cleavage of hydrazinium dications is a useful approach to macrobicyclic amines of the type developed by Park and Sim-mons , but the method does not appear to have been successfully applied to any cryptand syntheses. 

Trifluoromethanesulfonic (triflic) anhydride is commercially available or can be prepared easily by the reaction of triflic acid with phosphorus pentoxide [66] This moderately hygroscopic colorless liquid is a useful reagent for the preparation of various organic derivatives of triflic acid A large variety of organic ionic triflates can be prepared from triflic anhydride A recent example is the preparation of unusual oxo-bridged dicatiomc salts of different types [SS, 89, 90, 91, 92, 93] (equations 38-44) Stabilized dication ether salts of the Huckel aromatic system and some other systems (equations 38 and 39) can be prepared in one step by the... 

Cyclic dication ether triflate salts can be prepared by the reaction of diamides with tnflic anhydnde [91] (equation 43). 

The major product obtained from the reaction of TeCU with (McsSijsN is determined by the stoichiometry. When approximately equimolar amounts of the two reagents in THF are used the dimeric cluster TceNs (stabilized by coordination to four TeCU molecules) is obtained in high yields (Section 5.2.8). When the same reaction is carried out in acetonitrile with a molar ratio of 2 1, followed by treatment of the product with AsFs in SO2, [Tc4N2Cl8][AsF6]2 is obtained Section The dication [Tc4N2Cl8] in this salt is the dimer of the hypothetical tellurium(IV) imide [Cl3Te-N=TeCl]. ... 

The calculated barrier to dissociation of the [S3N2] dication into [SN]" and [S2N] in the gas phase is 10.9 kcal mof . However, lattice-stabilization effects allow the isolation of [MEg] salts (M = As, Sb) of this six r-electron system in the solid state from the cycloaddition of [SN] and [S2N] cations in SO2 (Eq. 5.11)."° The S-S and S-N bond distances in the planar, monomeric dication are shorter than those in the... 

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