Strong cations

The positive charge on carbon and the vacant p orbital combine to make carbo cations strongly electrophilic ( electron loving or electron seeking ) Electrophiles are Lewis acids (Section 117) They are electron pair acceptors and react with Lewis bases (electron pair donors) Step 3 which follows and completes the mechanism is a Lewis... 

As noted earlier, ion-exchange materials are grouped into four specific classifications depending on the functional group attached strong-acid cation, strong-base anion, weak-acid cation, or weak-base anion.. In addition to these, we also have inert resins that do not have chemical properties. 

A certain crown ether having additional coordination sites for a trasition metal cation (71) changes the transport property for alkali metal cations when it complexes with the transition metal cation 76) (Fig. 13). The fact that a carrier can be developed which has a reversible complexation property for a transition metal cation strongly suggests that this type of ionophore can be applied to the active transport system. 

NP, WP, P = non polar, weakly polar, polar, respectively SCX, SAX, WAX = strong cation, strong anion, weak anion exchanger, respectively. 

Viscosities of ionic liquids are several tens to hundreds times higher than that of water at room temperature. The structure of the cation strongly influences viscosity longer alkyl chains in the cation make the liquid more viscous. The viscosity of an... 

The J( Sn- Sn) values are less affected by the nature of the counter cation. Strong ion pairing has also been documented in the polyphosphide Zintl ions, such as LisPy [37]. 

The key requirement for a SET step in the photocatalytic process seems to be the surface complexation of the substrate, according to an exponential dependence of the probability of electronic tunneling from the distance between the two redox centers [66]. However, as was pointed out in the preceding section on the key role of back reactions, the presence of a SET mechanism could be a disadvantage from an applicative point of view. If the formed SET intermediate (e.g., a radical cation) strongly adsorbs and/or does not transform irreversibly [e.g., by loss of CO from a carboxylic acid or fast reaction with other species (e.g., superoxide or oxygen)], it can act as a recombination center, lowering the overall photon efficiency of the photocatalytic process. 

Transition from a neutral azole to an azolium cation strongly increases the TT-deficiency. In azines, the HOMO is normally occupied by the nonbonded electron pair of a nitrogen atom. By contrast, in azoles the HOMO is of the rr-type. This is supported by the parallel behavior of calculated HOMO... 

The key feature of the NMR spectra of 91 is its simplicity. Thus the 13C NMR spectrum consists of only two resonances at 4.9 and 17.6 ppm, indicating either a symmetrical trishomocyclopropenium cation, 93, or rapid equilibration between three equivalent structures (Scheme 37). The positions of the 13C NMR resonances of the cation strongly suggested the formulation of its structure as the trishomocyclopropenium ion, 93210. This conclusion was reinforced by the preparation of the deuterated cation and examination of the isotopic perturbation of its 13C chemical shifts208 211, and measurement of the 13C H coupling constants209. 

If two different C4H7 + ions may exist, which is the more stable The fact that most cyclobutyl derivatives seem to solvolyze directly to the cyclopropylcarbinyl cation strongly suggests that that ion is the more stabilized. Nuclear magnetic resonance studies, however, give conflicting information. The spectrum of the unsubstituted cyclopropylcarbinyl cation in superacid solution is most... 

Type of ion-exchanger Strong cation Strong cation Weak anion Strong anion... 

Ce), correlate well with solution properties (see Section F), hydride affinities of smaller cations strongly depend on the number of heavy atoms [22] and are, therefore, of limited value for the chemistry in solution. 

Since silyl cations coordinate to "inert" species like methane or the noble gases, it is little wonder that the organosilicon species which have been observed in condensed phases are not really silyl cations. Strong interaction with solvent molecules or counterions always are present. 

Peptidyltransferase assays have also provided insight into the mechanisms whereby spermine promotes, and NHJ ions inhibit, polypeptide synthesis on the ribosomes of S. solfataricus, T. tenax and D. mobilis (see section 3.3). First, the 30S uncoupled peptidyltransferase activity is absolutely dependent on spermine while being totally unaffected by monovalent cations. Secondly, monovalent cations strongly inhibit the 30S subunit coupled reaction [66]. Thus, polyamines appear to be obligatorily required to convert the catalytic center of the spermine-dependent ribosomes into an active conformation, whereas monovalent cations inhibit polypeptide synthesis by preventing 30S subunits from interacting with the cognate SOS particles (ref. [66], see below). 

Strong base cations) — (Strong acid anions) = alkalinity = acid neutralizing capacity = y (Weak acid anions) — (Weak acid cations) (6)... 

Dealkalizing Weak Acid Cation Strong Base Anion... 

The liquid range of HMPA is 7.2-235°C its dielectric constant is 30 (20" C). HMPA solvates cations strongly, whereas anions are less solvated. Unlike carboxamides, such as DMF, it is not attacked by aqueous alkali at t < SO C, and it is very resistant toward nucleophilic attack [377] but forms peroxides under the influence of light and oxygen [376]. 

The most common geometries adopted by group 4 catalysts are depicted in Scheme 1. In all practical cases, the active center is a cationic, strongly electrophilic metal complex capable of activating the C=C double bond of the inserting monomer. This positive charge of the complex cation is counterbalanced by a weakly (or non-) coordinating... 

Crowns and cryptands are able to increase considerably the basicity of a given base, owing to their extraordinary cationic complexation power. Thus A M+ in the presence of crowns or cryptands will see its M+ cation strongly complexed leading to A- as a nacked ion . In fact, the anion is not completely nacked as it may be seen for example from the use of crowns as transfer agents in phase-transfer catalysis reactions107. ... 

External quenching during protonolysis of unactivated cyclopropanes is rare, since the strong acids necessary to protonate these substrates are very poor nucleophiles. Generally proton elimination from the intermediate propyl cation strongly predominates. 

Recent results by Saunders and coworkers with the double-labeled 2-butyl-1,2- C2 and 2-butyl-2,3- C2 cations strongly support the protonated cyclopropane intermediate in the isotope scrambling process. 

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