P-Halogen

Ab-initio calculations are particularly usefiil for the prediction of chemical shifts of unusual species". In this context unusual species" means chemical entities that are not frequently found in the available large databases of chemical shifts, e.g., charged intermediates of reactions, radicals, and structures containing elements other than H, C, O, N, S, P, halogens, and a few common metals. 

Conjugate addition to a P-halogen substituted methaciylate results in an addition—elimination reaction which regenerates the tZ,/ -unsaturated moiety (19-21). 

Cationic Starches. The two general categories of commercial cationic starches are tertiary and quaternary aminoalkyl ethers. Tertiary aminoalkyl ethers are prepared by treating an alkaline starch dispersion with a tertiary amine containing a P-halogenated alkyl, 3-chloto-2-hydtoxyptopyl radical, or a 2,3-epoxypropyl group. Under these reaction conditions, starch ethers are formed that contain tertiary amine free bases. Treatment with acid easily produces the cationic form. Amines used in this reaction include 2-dimethylaminoethyl chloride, 2-diethylaminoethyl chloride, and A/-(2,3-epoxypropyl) diethylamine. Commercial preparation of low DS derivatives employ reaction times of 6—12 h at 40—45°C for complete reaction. The final product is filtered, washed, and dried. 

Because of thetr electron deficient nature, fluoroolefms are often nucleophihcally attacked by alcohols and alkoxides Ethers are commonly produced by these addition and addition-elimination reactions The wide availability of alcohols and fliioroolefins has established the generality of the nucleophilic addition reactions The mechanism of the addition reaction is generally believed to proceed by attack at a vinylic carbon to produce an intermediate fluorocarbanion as the rate-determining slow step The intermediate carbanion may react with a proton source to yield the saturated addition product Alternatively, the intermediate carbanion may, by elimination of P-halogen, lead to an unsaturated ether, often an enol or vinylic ether These addition and addition-elimination reactions have been previously reviewed [1, 2] The intermediate carbanions resulting from nucleophilic attack on fluoroolefins have also been trapped in situ with carbon dioxide, carbonates, and esters of fluorinated acids [3, 4, 5] (equations 1 and 2)... 

The physicochemical properties of carbon are highly dependent on its surface structure and chemical composition [66—68], The type and content of surface species, particle shape and size, pore-size distribution, BET surface area and pore-opening are of critical importance in the use of carbons as anode material. These properties have a major influence on (9IR, reversible capacity <2R, and the rate capability and safety of the battery. The surface chemical composition depends on the raw materials (carbon precursors), the production process, and the history of the carbon. Surface groups containing H, O, S, N, P, halogens, and other elements have been identified on carbon blacks [66, 67]. There is also ash on the surface of carbon and this typically contains Ca, Si, Fe, Al, and V. Ash and acidic oxides enhance the adsorption of the more polar compounds and electrolytes [66]. 

The main problem is knowing how to write the equation of the most energetic hypothetical reaction. Here are some rules that can be applied in the simplest case in which the molecule contains C, H, O, N, X p< = halogen) atoms ... 

The data in Table 4.4 for halogenated 2,2-difluoropropanes indicate a similar shielding influence by P-halogens on secondary CF2 groups.5,6... 

TABLE 4.3. WF Chemical Shifts of Primary CF2H Compounds—Effect of P-Halogen... 

P-Halogens also give rise to shielding of the fluorines of CF2C1 groups (Table 4.5).4... 

Data related to the effect of P-halogen on the proton and carbon chemical shifts of CF2H or CF2 groups are scarce (Scheme 4.13), although there is a recent review of 13C spectra of chlorofluorocyclo-propanes.3... 

On the other hand, P-halogen substituents appear not to affect the axial fluorine much, but deshield the four equatorial fluorines (Scheme 7.25). 

Construction of isolated or benzannulated five-membered rings of NHPs can be accomplished by means of various condensation or cycloaddition reactions all of which involve interaction of an electrophilic Pj and a nucleophilic C2N2 building block. Salts containing 1,3,2-diazaphospholide anions or 1,3,2-diazaphospholenium cations can be directly accessed by some of these reactions but the products are in most cases neutral 1,3,2-diazaphospholes or NHP. A particularly concerted effort has been directed toward the synthesis of P-halogen-substituted NHP which are capable of undergoing further reactions via halide displacement or halide abstraction and serve thus as entry points for the preparation of a wide variety of neutral and cationic NHP derivatives. 1,3,2-Diazaphospholide anions are normally accessed by deprotonation of suitable iV-H-substituted precursors. 

Reactions of P-halogen-NHPs with Lewis acids leading to halide abstraction, or metathetic replacement of the halide by a nucleofugic, noncoordinating anion form by far the most important routes to access phosphenium ions in general [51, 52] and also 1,3,2-diazaphospholenium cations in particular. As Lewis acid assisted P-X... 

Routine identification and analytical characterization of all types of NHPs was preferably carried out by multinuclear NMR spectroscopy. Of particularly high diagnostic value are 31P NMR spectra where rather specific chemical shift ranges for heterocycles with different types of P-substituents can be observed. The largest chemical shifts occur for anionic and neutral 1,3,2-diazaphospholes (220-300 ppm) and 1,3,2-diazaphospholenium cations (210-200 ppm). Chemical shifts of P-halogen-l,3,2-diazaphospholenes vary over an overall range of 200-110 ppm and decrease in the order I (205-190 ppm)>Br (194-185 ppm two compounds... 

Comprehensive studies of molecular structures of neutral NHPs have been in particular performed for P-halogen, P-amino, and P-phosphino derivatives in... 

Apart from characterization of the individual types of six-membered heterocycles by routine spectroscopic methods, several cationic cyclic diketiminato-phosphenium ions and 1,8-diamidonaphthalene-derived P-chlorophosphines and phosphenium ions, respectively, were characterized by single-crystal X-ray diffraction studies. The P-halogen- and P-hydroxy-substituted cyclic diketiminato-phosphenium ions 28... 

Detailed investigations of the chemical reactivity of the diketiminato-stabilized phosphenium cations like 28 (Scheme 17) are to date rare and include only two reports dealing with the substitution and reduction of P-halogen-derivatives. Thus, reaction of 28 (X=Br) with sodium hydroxide in toluene was reported to proceed with displacement of the halide substituent at phosphorus and conservation of the heterocyclic ring to give a mixture of bromide and triflate salts containing a P-hydroxy-substituted cation, both of which were isolated in small yields [89], The products are remarkable as they represent one of very few examples of a stable phosphinous acid which does not rearrange to the tautomeric secondary phosphine oxide. Potassium reduction of the P-chloro-substituted derivative 34 produced the... 

On the basis of this argument it is probable that the tris-p-halogen substituted trityl salts will be useful initiators for the polymerisation of isobutylene since their ionisation potentials probably exceed 690 kj mol1 [38], and the p-substitution would inhibit the back-biting reactions which make both trityl and dityl salts unstable [39]. 

The Kirsanov reaction (Scheme 5) is a valuable supplement to the Staudinger reaction starting from phosphorus pentachloride and amine or amide derivatives it opens an access to P-halogenated iminophosphorane 9 (50IZV426). 

The P-halogenated iminophosphoranes can be subsequently transformed into trialkyl-, triaryl-, and trialkoxyiminophosphoranes by nucleophilic substitution [56ZOB903, 56ZOB907 66MI1 75JCS(D)2527 89MI1]. 

XjYs structure, type, 35 283 Halo-chalcogenates(IV), 35 246-255 degradation, 35 247-248 di-and trinuclear anions, 35 247, 249-251 hexahalochalcogenates(IV), 35 251-253 nonahalodichalcogenates(IV), 35 252-253 polymeric species, 35 254-255 in solvents, 35 247 Haloenzyme, 22 424 p-Halogen, see Parahalogen Halogenation, of hexafluoroacetone, 30 302-303... 

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