Ion reagent

The predominance of a-substituted products in the reaction of 2,4,6-tribromopyridine in phenol solution may result from competitive attack by free phenol in preference to attack by the phenoxide ion reagent involving structures 18 (B = base) or 19. A wealth of chemistry awaits elucidation by physical-organic studies. 

G. (1999) Structural chemistry of uranium associated with Si, Al, Fe gels in a granitic uranium mine. Chem. Geol. 158 81-103 Allen, G.C. Kirby, C. Sellers, R.M. (1988) The effect of the low-oxidation-state metal ion reagent tris-picolinatovanadium(II) formate on the surface morphology and composition of crystalline iron oxides. J. Chem. Soc. Faraday Trans. I. 84 355-364... 

In essence, hydride ion reagents reduce chromanones to chromanols (81T2613), the reaction often being stereospecific (70JCS(C)1006). 

D. Fluorocarbon Polymers. Four different fluorocarbons account for the bulk of the laboratory applications polytetrafluoroethylene, Teflon PTFE po-ly(chlorotrifluoroethylene), KEL-F tetrafluoroethylene-hexafluoropropylene copolymer, Teflon FEP and tetrafluoroethylene-perfluorovinyl ether copolymer, PFA. These polymers are inert with most chemicals and solvents at room temperature and exceptionally inert with oxidizing agents. They also have an exceptional resistance to temperature extremes. However, they are decomposed by liquid alkali metals, solutions of these metals in liquid ammonia, and carban-ion reagents such as butyllithium. Teflon retains some of its compliance at liquid hydrogen temperature. The maximum temperature which is recommended for continuous service is 260°C for Teflon PTFE and PFA, and about 200°C for Kel-F and Teflon FEP. 

Reactions of a, [1, /J-trifl uorostyrenc and chloro-a, /i-difluorostyrene with 9-methylfluoren-9-yl anion (potassium salt) are accelerated by ion-pair solvating agents (18-crown-6, [2.2.2]-cryptand) and retarded by KBPI14 as a common-ion reagent.5 This was interpreted as indicating that solvent-separated ion pairs are more reactive than contact ion pairs in these reactions. 

The synthetic utility of hydrogen peroxonium ion reagent is discussed in Chapter 5. Similarly, protonation and cleavage reactions of hydroperoxides and peroxides have been investigated extensively125 and are also discussed in Chapter 5. 

Positive Ion Reagent Gases for Chemical Ionization Mass Spectrometry... 

The C-H bonds at the P position relative to R3M- (M = Si, Ge, Sn, Pb) substituents are activated towards attack by electrophilic reagents. Two types of electrophilic attack at a P C-H bond are considered in Scheme 3 Path 1 involves hydride abstraction by the electrophile, resulting in the formation of a carbenium ion intermediate, a process that is assisted by the metal P-effect. Such a pathway might be expected to be followed by strongly Lewis acidic reagents, such as carbenium ion reagents. 

Using a Paired-Ion Reagent of the Same Charge as the Sample... 

For strongly acidic samples (those that are completely ionized at pH 2), it is necessary to take advantage of the strongly ionic nature of the sample. By adding a buffer to control pH and to ensure that the sample maintains ionic character, and by adding a suitable compound (in this case a quaternary ammonium salt) as a paired-ion reagent, the retention of the acid will increase. 

Reversed-phase chromatography has also been used to separate proteins. However, the required use of alcoholic gradients or paired-ion reagents with the reversed-phase support should be avoided, to cancel the potential for inactivation of the enzymatic activities. 

Fig. 8. Capacity factor dependencies for several peptides separated on a /.i-Bondapak C]8 column as a function of pH in the presence of a fixed concentration pairing ion reagent. The eluent was 20 methanol-809f water-50 mM NaHjPO,-15 mM HjPOi-lO mAf sodium hexane sulfonate, titrated with 10 M NaOH over the range pH 2.5-7.0 flow rate I ml/min. The peptides were as follows 2, G.G. 5, G.F. amide 6, R.F. 8, F.L. amide 10, G.L.Y. 11, G.G.Y. 12, R.F.A. The one-letter code is A, Ala G, Gly F, Phe L, Leu Y, Tyr R, Arg.

The combination of a source of electrophilic halogen together with a fluoride ion reagent permits efficient halofluorination of nucleophilic carbon-carbon double bonds products resulting from addition in a trans stereochemistry are usually obtained (Figure 3.62). 

Crystals of the hydrated ammonium salt of [CrafCOa) " form by slow mixing of the ammonium carbonate and Cr(II) ion reagents through a gel. ... 

Ion Reagent Wavelength, nm Absorption Fluorescence Sensitivity, p.g/mL Interference... 

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