Self-terminating

Domino effeets eliminated so that adverse events are self-terminated and do not initiate new events. 

A useful self-terminating catalyst system (77), employs a Pd catalyst [prepared from Pd(OAc)2, NaH, and r-AmOH in THF]. The solvent required for the hydrogenation depends on the acetylene structure monosubslituted acetylenes require solvents such as hexane or octane, whereas disubstituted acetylenes need ethanol, ethanol-hydrocarbon, or ethanol-THF mixtures. In all cases it was necessary to use quinoline as a catalyst modifier. The authors consider this system one of the best for achieving both high yield and stereoselectivity. 

A characteristic of free radicals is the bimolecular radical-radical reaction which in many cases proceeds at the diffusion-controlled limit. These radical-radical reactions can occur either between two identical radicals or between unlike radicals, the two processes being known as self-termination and cross-termination reactions, respectively. 

Kinetic ESR spectroscopy has been used to determine the rate constants for self-termination of MeS02, EtS02, PhSO 2 and 2,5-Cl2C6H3S02 radicals18. At 233 K and in cyclopropane as a solvent the values found for 2k, were in the range (4.5 1.5) x 109 m" 1 s 1 for all RSO 2 radicals. 

Selenosulphonylation 191, 194, 1107-1109 Selenoxides, as oxidizing agents 253 Self-termination, of radicals 1084, 1085,... 

A characteristic reaction of free radicals is the bimolecular self-reaction which, in many cases, proceeds at the diffusion-controlled limit or close to it, although the reversible coupling of free radicals in solution to yield diamagnetic dimers has been found to be a common feature of several classes of relatively stable organic radicals. Unfortunatly, only the rate constants for self-termination of (CH3)jCSO (6 x 10 M s at 173 K) and (CH3CH2)2NS0 (1.1 X 10 M s at 163K) have been measured up to date by kinetic ESR spectroscopy and consequently not many mechanistic conclusions can be reached. 

Episodes of torsades de pointes may self-terminate, with frequent recurrence. 

The above equation is valid provided the rate of alkyl radicals self-termination is neglected, which is well possible when the polymer contains a sufficiently high level of oxygen. 

Analysis of the Bolland-Gee scheme involving the self-termination of peroxyl radicals and peroxyl radicals with alkyl radicals using Equations (4-8) leads to the relation... 

In addition to cross-propagation reactions, one cross-termination reaction is introduced in addition to two self-termination reactions, viz,... 

The extent to which chain oxidation is inhibited depends on the activity and concentration of the antioxidant. A specific activity of an antioxidant as a retarding agent should be expressed per unit concentration of the inhibitor. If the antioxidant terminates chains, chain self-termination by the reaction of peroxyl radical disproportionation should be taken into account. As a result, one obtains the following expression for estimation of the activity F of the introduced amount of the antioxidant [18] ... 

Note that methacrylonitrile lacks an acidic hydrogen for self-termination of chains. 

Sustained VT is that which requires therapeutic intervention to restore a stable rhythm or that lasts a relatively long time (usually longer than 30 seconds). Nonsustained VT self-terminates after a brief duration (usually less than 30 seconds). Incessant VT refers to VT occurring more frequently than sinus rhythm, so that VT becomes the dominant rhythm. Monomor-phic VT has a consistent QRS configuration, whereas polymorphic VT has varying QRS complexes. Torsade de pointes (TdP) is a polymorphic VT in which the QRS complexes appear to undulate around a central axis. 

T Depends on rate constants for radical self-termination reactions. g Rate constants for reaction of Bu3SnD. 

On addition of S04 to the triple bond in the lO-member cycloalkyne 24 and cyclo-aUcynone 27, a nonchain, and anionic, self-terminating radical cyclization cascade is induced. In the former reaction (equation 22) the bicyclic ketones 25 and 26 are formed, and in the latter reaction (equation 23) the a,/3-epoxy ketones 28 and 29 are formed in good yields. Because of the difficulty of oxidizing isolated triple bonds, 804 does not react as an electron-transfer reagent in these reactions but acts as a donor of atomic oxygen. 

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