SEAr mechanism

In some instances, especially with the oxygen and sulfur heterocycles, the overall reaction leading to a substituted product does not involve an SEAr mechanism but proceeds by an addition followed by elimination sequence, as outlined for the bromination of coumarin in equation (4). The choice of experimental conditions can affect the outcome of the reaction, as illustrated in the formation of (114) and (115) in Section 3.2.1.4.7. 

A further study of 2-nitraminopyridine and its 3-, 4-, 5-, and 6-methyl-, 5-bromo-, and 5-nitro derivatives showed that in sulfuric acid, free nitro-nium ions are produced (added mesitylene becomes nitrated). The relative rates of nitration at the 3- and 5-positions of the methyl derivatives are shown in Table 9.4. The results for the 4-methyl compound show that a normal SEAr mechanism is not involved. 5-Methyl-2-nitraminopyridine seemed to react by a different route since a considerable amount of 5-... 

Screw pumps, viscous material 329 Seals, mechanical 339 Sears. F, W. 172.179... 

B. D. Sanford, C. R. Dacar, and S. M. Sears. Acid fracturing with new fluid-loss control mechanisms increases production. Little Knife field. North Dakota. In Proceedings Volume, pages 317-324. SPE Rocky Mountain Reg Mtg (Casper, WY, 5/18-5/21), 1992. 

F. W. Sears, An Introduction to Thermodynamics, The Kinetic Theory of Gases, and Statistical Mechanics, 2nd edn., Addison-Wesley, Reading, Massachusetts, 1966. 

Lippiello PM, Sears SB, Fernandes KG (1987) Kinetics and mechanism of L-[ H]nicotine binding to putative high affinity receptor sites in rat brain. Mol Pharmacol 31 392-400... 

The situation improved with the introduction of the wheel-lock (Fig 1), which produced its own fire by mechanical action, in the early 16th century. This name was used because of the prominent wheel which was rotated to produce fire. In addition to the wheel, the mechanism consisted essentially of the cock, the mainspring, and the sear. The wheel was serrated to provide a rough surface. The cock was a clamp which held a small piece of iron pyrites. Iron pyrites is a mineral which, when rubbed against a roughened piece of metal, will produce sparks... 

Sear, a) An item so designed as to retain the firing mechanism of a gun in the cocked position. b) A variety of lockwork in the firing mechanism of a proplnt actuated device which prevents motion of the firing pin until released Ref Anon, OrdTechTerm (1962), 266-R... 

Sears, F. W. Introduction to Thermodynamics, Kinetic Theory, and Statistical Mechanics," pp. 123-124, Addison-Wesley Publishing Company, Inc., Reading, Mass., 1953. 

The mechanisms of the Gattermann and Gattermann-Koch formylation belong to the category of electrophilic aromatic substitution (SEAr) but are not known in detail, since they have a tendency to vary from one substrate to another, and the reaction conditions may also play a role. When carbon monoxide is used, the electrophilic species is believed to be the formyl cation, which is attacked by the aromatic ring to form a -complex. This -complex is then converted to the aromatic aldehyde upon losing a proton. When HCN is used, the initial product after the SEAr reaction is an imine hydrochloride, which is subsequently hydrolyzed to the product aldehyde. 

Changes in the thermal properties of SC films were correlated with effects on the mechanical properties of film, i.e., reduced film strength and increased film elongation. Plasticizations disrupt intermolecular interactions between polymer molecules with the effect of decreasing brittleness and increasing film flexibility (Sears and Darby, 1982). Lillie and Gosline (1993) pointed out that the Tg of proteins, especially at a low water content, may occur over a wide temperature range. However, few Tg data are available for proteins (Roos, 1995). 

Sears CL, Kaper JB. Enteric bacterial toxins mechanisms of action and linkage to intestinal secretion. Microbiol Rev 1996 60 167-215. 

Abstract Azines, diazines or thiazole (V-oxides are highly reactive substrates in palladium-catalyzed direct arylation reaction. For these reactions, the results are inconsistent with an SEAr reaction pathway and may best fit with a concerted metalation-deprotonation-like (CMD) mechanism. 

Palladium-catalyzed arylations of simple electron-rich five-membered heteroarenes with one heteroatom, such as furans, thiophenes, and pyrroles, with aryl iodides, bromides, or chlorides are among the most frequently studied direct arylation reactions [31, 39, 85]. These reactions usually afforded five-membered heterocycles, which were arylated at the position adjacent to the heteroatom in moderate to good yields. These reactions were mainly accomplished with electrophilic catalysts and proceeded more efficiently using aryl bromides with electron-withdrawing groups. This is in agreement with an electrophilic SEAr-type mechanism relying on a palladium(0)/palladium(ll) manifold [86]. Selected results of catalytic direct arylations of simple electron-rich five-membered heteroarenes (124—126) with aryl iodides, bromides, or chlorides are summarized in Table 9.2. 

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