Influence of alkene structure on the formation constants of alkene–ICl molecular complexes

Abstract

The experimentally determined rate law for the addition of IC1 to 22 alkenes in CC14 at 25OC under conditions of (alkene)o > > (ICl)o is -d(ICl)/dt = k,,,(alkene)o(~~1)3/{l + C2(alkene)o} 3. The constant C2 is shown to be equal to K,,, which is a measure of the formation constant or constants of the molecular complexes in this system. Under the experimental conditions used, C2 is a good approximation of the formation constant of the 1:l alkene-IC1 molecular complex. Thus the values of C2 obtained allow an estimate of the effect of alkene structure on the formation constant of the first molecular complex involved in this addition reaction. The contribution of the effect of substituents on C2 is estimated to be approximately 24% of the overall change in rate due to change in the alkene structure. GEORGE H. SCHMID et JAMES W. GORDON. Can. J . Chem. 64, 2171 (1986) Operant dans le CC14, a 25°C et dans des conditions ou la ( a l~e n e )~ >> (ICl)o, on a dCterminC expkrimentalement que la loi de vitese pour l'addition du ICl sur 22 alcknes est dCfinie par 1'Cquation -d(ICl)/dt = k,,,(al~kne)~(1C1)~/{1 + ~~( a l c k n e )~}~. On dCmontre que la constante C2 est Cgale a K,,, qui est une mesure de la constante de formation ou des constantes des complexes molCculaires impliquCs dans ce systeme. Dans les conditions experimentales utilisCes, C2 est une bonne approximation de la constante de formation du complexe molCculaire 1 : 1 alcene/ICl. Les valeurs de C2 obtenues permettent donc dlCvaluer I'effet de la structure de l'alckne sur la constante de formation du premier complexe molCculaire impliquC dans cette reaction d'addition. On a Cvalut que la contribution de l'effet des substituants sur Cz est Cgale a environ 24% du changcmcnt global dans la vitesse du a un changement dans la structure de l'alcene.[Traduit par la revue]There is ample evidence in the literature (1-3) that molecular complexes or charge transfer complexes (CTC) as they are also called are involved on the reaction pathway prior to the rate determining step in electrophilic additions of bromine, chlorine, and iodine monochloride to alkenes. These complexes are defined according to Mulliken as o-T CTC (4).The existence of one or more complexes prior to the rate determining step introduces a complication in the interpretation of linear free energy relationships in electrophilic additions of bromine to alkenes because a change in alkene structure affects not only the rate determining step but also the value of the formation constant of the CTC. Thus the value of p obtained from such rate data is the sum of p for the formation of the complex or complexes and p for the rate determining step.Based upon data from CTC formed between ketones and bromine, it was concluded that the effect of structure on the formation constants of the CTC is much smaller than the kinetic substituent effect. Consequently, it was assumed that p for the formation constant of the CTC is negligible as compared to p for the rate determining step (5). While values of formation constants ...

Polarizability Effects and Dispersion Interactions in Alkene-Br2π-Complexes

“…It is noteworthy that in the addition of ICl to alkenes, an irreversible reaction, the substituent effects on the 1:1 ICl-alkene complexes contribute to the overall change in rate by ca. 24% . This may suggest a more important return in olefin bromination or a charge development in the π-complexes of caged alkenes larger than those of linear alkenes.…”

Electrophilic Addition to Alkenes: The Relation between Reactivity and Enthalpy of Hydrogenation: Regioselectivity is Determined by the Stability of the Two Conceivable Products

“…Additions of ICl to alkenes in CCl 4 solvent were studied by Schmid and Gordon 15. The rate expression was found to be complex and observed values of the rate constant k exp were found not to represent any one particular elementary step.…”

Soluble Chlorofullerenes C60Cl2,4,6,8,10. Synthesis, Purification, Compositional Analysis, Stability, and Experimental/Theoretical Structure Elucidation, Including the X-ray Structure of C1-C60Cl10

“…In this section we use frontier-orbital arguments to rationalize the observation that 14,28,29,31,SPP-C 60 Cl 10 is one of the most abundant isomers to be formed from SPP-C 60 Cl 6 . In general, the addition of ICl to olefins is first order in olefin and either second or third order in ICl. This suggests an iodonium intermediate followed by addition of a Cl − ion from the putative ICl 2 − anion, as shown in Scheme .…”