Possible criteria for distinguishing between cyclic and acyclic activated complexes and among cyclic activated complexes in addition reactions

Reaction of Chlorine Molecules with Unsaturated Submicron Organic Particles

“…The ambient temperature reaction between Cl 2 and alkenes bearing a side-chain on the double bond, such as iso-butene and other tertiary alkenes, are reported to undergo substitution exclusively, the double bond being retained as such [26]. Many data suggest that simple alkenes and chlorine react slowly, if at all, in the gas-phase at ambient temperature while the primary product is generally the dichloroalkanes [27,28]. With increasing temperature, the gas-phase reaction between alkenes and Cl 2 also begins to proceed through a substitutive mechanism [26].…”

Three-Dimensional Heterocycles: New Uracil-Based Structures Obtained by Nucleophilic Substitution at the sp2 Carbon of Bromoisoxazoline

“…The known exceptionally high reactivity and exclusive exo-selectivity of the cycloaddition reaction of 1 with the bromonitrile oxide 3 is akin to that of the related parent carbocyclic norbornene, which adds all types of reactants only on the exo face [16]. The origin of the norbornene selectivity is usually attributed to the relief of strain [17], geometric deformation of the double bond (pyramidalization due to torsional [18] and hyperconjugative effects [19]) as well as favourable staggering effects in the exo attack [20].…”

The chemistry of organohalogenic molecules. Part 172. Kinetic studies of bromine transfer from N-bromo-succinimide to norbornene under protic conditions

“…7,8 Halogen transfer from the N type of reagents is very sensitive to reaction conditions, especially in the case of fluorine transfer where acetonitrile as solvent affects the reactions to form Ritter type fluoroamides, whereas in the presence of a nucleophile vicinal fluoro-hydroxy or fluoro-alkoxy products are formed. [25][26][27][28] In order to obtain kinetic and thermodynamic activation information comparable to that on fluorine transfer, 29 we decided first to investigate the products formed in bromination of norbornene with NBS in acetonitrile in the presence of water.…”

“…[1][2][3][4][5][6] From these studies, two types of information can be obtained: the structures of the products and their distribution inform us about the type of electron shift from the π electron system to acceptor E-L reagent;1-6 the relative rates of functionalisation of norbornene versus cyclohexene inform us about the geometry of the rate determining transition state, 7 being insensitive in the case of a three-centered intermediate (mercuric acetate 8 ), but very sensitive for four-centered or larger intermediates in (picryl azide 9 a rate ratio up to 8 . 10 3 was observed).…”