Heavy-Atom Kinetic Isotope Effects, Cocatalysts, and the Propagation Transition State for Polymerization of 1-Hexene Using therac-(C2H4(1-indenyl)2)ZrMe2Catalyst Precursor

AbstractRates of HCN elimination from polycyanides N,N-dimethyl-4-(1,2,2-tricyanoethyl)-aniline (1), 9-cyano-9-dicyanomethyl fluorene (2), 1,1-diphenyl-1,2,2-tricyanoethane (3), and 2-phenyl-1,1,2-tricyanopropane (4) have been studied in methanol. Elimination from 1 occurs via (E 1 c B)R, mechanism. On the other hand olefin formation from 2-4 has been shown to occur via (E 1)anion pathway. Heavy atom kinetic isotope effects indicated that product stability is not the sole factor controlling the transition state geometries. Values of k12/k14 were found to be in the order 2 > 3 > 4 > 1 which implied transition states with more carbanion-like structure in the opposite direction. Solvent isotope effects and enthalpies of activation were also determined and discussed in terms of transition states geometries.

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Heavy-atom kinetic isotope effects in the acid-catalyzed and thermal rearrangements of 2,2'-hydrazonaphthalene. Transition-state differences in their concerted rearrangements

Journal of the American Chemical Society ◽

10.1021/ja00297a030 ◽

1985 ◽

Vol 107 (11) ◽

pp. 3218-3223 ◽

Cited By ~ 25

Author(s):

Henry J. Shine ◽

Ewa Gruszecka ◽

Witold Subotkowski ◽

Marilyn Brownawell ◽

Joseph San Filippo

Keyword(s):

Transition State ◽

Isotope Effects ◽

Heavy Atom ◽

Kinetic Isotope Effects ◽

Kinetic Isotope ◽

Thermal Rearrangements ◽

Acid Catalyzed

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Isotope effects in nucleophilic substitution reactions. III. The effect of changing the leaving group on transition state structure in SN2 reactions

Canadian Journal of Chemistry ◽

10.1139/v79-221 ◽

1979 ◽

Vol 57 (11) ◽

pp. 1354-1367 ◽

Cited By ~ 27

Author(s):

Kenneth Charles Westaway ◽

Syed Fasahat Ali

Keyword(s):

Transition State ◽

Nucleophilic Substitution ◽

Isotope Effects ◽

Heavy Atom ◽

Substituent Effects ◽

Kinetic Isotope Effects ◽

Substitution Reactions ◽

Nucleophilic Substitution Reactions ◽

Kinetic Isotope ◽

Leaving Group

The nucleophilic substitution reactions of a series of 4-substituted phenylbenzyldimethyl-ammonium ions with thiophenoxide ions at 0 °C in N,N-dimethylformamide have been used to demonstrate how a change in the leaving group alters the structure of the SN2 transition state. Heavy atom (nitrogen) kinetic isotope effects, secondary α-deuterium kinetic isotope effects and Hammett ρ values provide qualitative descriptions of both the nucleophile–α-carbon and α-carbon–leaving group bonds in the transition states of these reactions. The results indicate that changing to a better leaving group causes the bond between the α-carbon and the nucleophile to be much more fully formed while the bond to the leaving group is essentially unchanged. The results are discussed in the light of current theories of substituent effects on SN2 reactions and a possible explanation for the surprising results (i) that the greatest effect is in the bond more remote from the point of structural change and (ii) that more nucleophilic assistance is required to displace a better leaving group is given.

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