Carbon-carrying ions

The few exceptions to this general rule arise when the a-carbon carries a substituent that can stabilize carbonium-ion development well, such as oxygen or sulphur. For example, 1-trimethylsilyl trimethylsilyl enol ethers give products (72) derived from electrophilic attack at the /J-carbon, and the vinylsilane (1) reacts with a/3-unsaturated acid chlorides in a Nazarov cyclization (13) to give cyclopentenones such as (2) the isomeric vinylsilane (3), in which the directing effects are additive, gives the cyclopentenone (4) ... 

ESR spectra of ion-radicals reveal the quantitative distribution of spin density. The ESR spectrum determines the HEC constant for the ith hydrogen, flT. The constant is directly proportional to the spin density at the ith carbon carrying the ith hydrogen. 

The racemization of an optically active secondary halide with the chiral carbon carrying the halogen (e.g., 2-chlorobutane) may occur ift solution and, usually, the more polar and better ionizing the solvent is, the more readily the substance is racemized. Ionization of the halide by an SK1 process probably is responsible, and this certainly would be promoted by polar solvents (see Section 8-6). All indications are that an alkyl carbocation once dissociated from its accompanying anion is planar and, when such an ion recombines with the anion, it has equal probability of forming the d and L enantiomers ... 

The mass determination of ionic species (atomic or polyatomic ions) in mass spectrometry is always a comparative measurement, which means the mass of an ionic species is determined with respect to reference masses of elements (or substances) used for mass calibration. The reference mass is thus acquired from the mass unit (m = In = 1/12) of the mass of the neutral carbon isotope (m = 1.66 X 10 kg). A mass calibration is easy to perform in solid-state mass spectrometry if the sample contains carbon (using carbon cluster ions with whole masses, as discussed above). The so-called doublet method was apphed formerly, e.g., ions and doubly charged Mg + forming a doublet at the same nominal mass number 12 were considered, where they are slightly displaced with respect to one another. The doublet method is no longer of relevance in modern inorganic mass spectrometry. Orientation in the mass spectra can be carried out via the matrix, minor and trace elements after mass calibration and by comparing the measured isotopic pattern of elements with theoretical values. 

Thus the absence of isotope effects establishes not only the two-step nature of electrophilic aromatic substitution, but also the relative speeds of the steps. Attachment of the electrophile to a carbon atom of the ring is the difficult step (see Fig. 11.2) but it is equally diflicult whether the carbon carries protium or deuterium. The next step, loss of hydrogen ion, is easy. Although it occurs more slowly for deuterium than for protium, this really makes no difference slightly faster or slightly slower, its speed has no effect on the overall rate. 

To this purpose, isotopic data presented in this paper were obtained from several selected Gorleben groundwaters as part of the colloid characterisation programme. The contents of major and minor ions, light isotopes ( H, H, and and the U/Th isotopes were measured. Radiocarbon and were measured in dissolved inorganic carbon (DIG), ion the humic acid (HA-colloids) and fulvic acid (FA-solution) fractions of dissolved organic caibon (DOC). The and were also determined in dissolved sulphate phase. The U/Th isotope measurements were carried out on total and surface solid phases, colloid fraction (1-1000 nm particle size, HA) and solution (<1.5 nm, FA). 

Adsorption from solutions onto solid surfaces is important in many industrial practices, such as dye or organic contaminant removal, edible oil clarification by activated carbon, and ion exchange, where the adsorption of ions from electrolyte solutions is carried out. Adsorption from solution is also used in analytical chemistry in various chromatography applications. On the other hand, surfactant, polymer and biological material adsorption on solids, to modify the surface of solid particles in stabilizing dispersions, are also very important industrial fields. 

The ionic addition of unsymmetrical addends to alkenes obeys the Markov-nikov rule. For the addition of HX, the Markovnikov transition state of C-H bond formation is encouraged by symbiosis. The creation of a more highly substituted carbocation is favored because the central carbon carries fewer soft hydrogen atoms. The carbenium ion may also be considered as an acid-base complex of a carbene-cation in which the carbene is a donor. Thus, the secondary carbenium ion RjCH is made up of a resonance hybrid HRCi R R CHR, and the primary ion RCHf is... 

The protons shown are non-eqjiivalent (because of the unsymmetrical conformation of the OEt) and appear as a multiplet at 5 4.14—4.4, which is taken to imply delocalization of charge on to the carbons carrying them. The related ion (110) is less stable than (107) and gives both possible adducts with PPhj, and (111) is also less stable. The edge of the cyclobutene is thus more stabilizing than a n-bond at the same site. 

The mechanism of these reactions probably usually involves direct nucleophilic attack on the carbon system of the coordinated triene, although initial attack on coordinated carbon monoxide or on the metal, followed by rearrangement, may occur in some cases. Nucleophilic displacement of halogen from aryl halides is facilitated by coordination of the ring to the tricarbonyl-chromium group [Eq. (52)], but the reaction mechanism is more complicated than simple nucleophilic attack at the carbon carrying the chlorine atom, followed by elimination of chloride ion. Attack takes place at both ortho and meta positions in the aryl ring (Semmelhack and Hall, 1974) [Eq. (48)]. 

The local appearance of the reaction product is determined by the current-carrying ion. While for acidic fuel cells the reaction product shows up at the cathode (oxidant side), it is the anode (fuel side) for alkaline fuel cells. In case of C-containing fuels, e.g., methanol, a second reaction product containing the oxidized carbon appears at the... 

As mentioned with relation to the acids when the alpha carbon carries a substituent the rearrangement ion shifts in mass by the mass of the substituent. The isomeric pentonates, methyl isovalerate and methyl 2-methylbutyrate can readily be distinguished (Tanaka and Yu, 1973) because of the formation of mh 88 in the latter. 

---