Calculation of H/D carbon-12/carbon-13, and carbon-12/carbon-14 fractionation factors from valence force fields derived for a series of simple organic molecules

Hartshorn, S. R.; Shiner, V.J. Jr.

doi:10.1021/ja00781a004

Cited by 101 publications

(59 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…bond order-force constant relationships we have employed for these basic models are given in Table 6. These models are very similar to the constant bond order models used previously (5,(13)(14)(15)40) but it should be noted that none of these transition states will fit all the kinetic isotope data for the methyl iodide-chloride ion system (17). The first calculations we will consider will be those for vL = 0 and for total bond order, n, = 1 = n, + n,, withF,, = +(FcclFc,)'12(see Table 5) where the force constants for the CI and the CCl bonds are given in Table 6.…”

Section: Reaction Coordinares and The Product-like (Reactant-like) Chsupporting

confidence: 65%

¹³C kinetic isotope effects and reaction coordinate motions in transition states for S_N2 displacement reactions

Buddenbaum¹,

Shiner²

1976

Can. J. Chem.

View full text Add to dashboard Cite

Can. J. Chem. 54,1146 (1976. Reaction coordinate motions and "C kinetic isotope effects at 25 "C have been calculated for the S,2 reactions of methyl iodide with iodide, cyanide, and chloride ions and for the S,2 reaction of benzyl bromide with hydroxide ion using transition state models characterized by single interaction force constant, F,,, between the bond being formed and the bond being broken. The isotope effect calculations show that the dependence of calculated 13C isotope effects on transition state symmetry found by Willi and Sims er al. holds true for reaction barriers corresponding to small values of v,, while the symmetry dependence observed by Bron holds true for barriers corresponding to large values of v,. v, was also found to have a strong influence on the reaction coordinate motions of the transition states. In particular, for the methyl iodide reactions an increase in v, increases the distortion of the methyl group in the direction expected for a classical S,2 reaction. Finally, reaction coordinate motions were used to show that the model proposed by Bron for the borderline region between S,1 and S,2 reaction mechanisms predicts an increase in the "C kinetic isotope effect with decreasing total bond order and not the decrease suggested by Bron.WARREN EDWARD BUDDENBAUM et VERNON JACK SHINER, JR. Can. J. Chem. 54, 1146Chem. 54, (1976.On a calcule les mouvements des coordonnees de la reaction et les effets isotopiques cinetiques du 13C a 25 ' C pour les reactions S,2 de I'iodure de methyle avec les ions iodure, cyanure et chlorure et pour la reaction SN2 du bromure de benzyle avec I'ion hydroxyde en utilisant des modeles d'etats de transition caracterises par une constante de force pour une seule interaction, F,,, entre le lien qui se forme et le lien qui se brise. Les calculs d'effet isotopique montrent que la dependance des effets isotopiques de 13C sur la symetrie des etats de transition qui a ete trouvee par Willi et par Sims el al. prevaut pour des barrieres a la reaction correspondant a de petites valeurs de v,, alors que la dependance sur la symetrie observee par Bron prevaut dans les cas ou les barrieres a la reaction correspondent a des valeurs elevees de v,. On a aussi trouve que v, a une influence importante sur les mouvements des coordonnees de la reaction des etats de transition. En particulier, pour les reactions de I'iodure de methyle, une augmentation de v, augmente la distorsion du groupe mtthyle dans la direction attendue pour une reaction SN2 classique. Finalement, on a utilise les mouvements des coordonnees de reaction pour montrer quelle modele propose par Bron pour la region intermediaire entre les mecanismes de reaction S, I et SN2 predit une augrnenrarion de I'effet isotopique cinetique du 13C avec une diminution de I'ordre total de liaison et non pas une diminurion telle que sugeree par Bron.[Traduit par le journal]Theoretical considerations lead to the pre-the transfer of a carbon (C*) fragment between diction that primary hydrogen kinetic isotope two groups, X and Y ...

show abstract

Section: Reaction Coordinares and The Product-like (Reactant-like) Chsupporting

confidence: 65%

¹³C kinetic isotope effects and reaction coordinate motions in transition states for S_N2 displacement reactions

Buddenbaum¹,

Shiner²

1976

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…Detailed calculations for individual equilibrium reactions, taking higher order effects into account, show most 14 C-13 C fractionation ratios clustering around 1.85-1.9 (Stern and Vogel 1971;Hartshorn and Shiner 1972). Furthermore, expressions similar to Equation A9 can be derived for kinetic fractionation for non-equilibrium reactions (Melander 1960;Wolfsberg 1972), implying similar mass dependence.…”

Section: Appendix A: Isotopic Fractionation In Chemical Equilibria Anmentioning

confidence: 79%

Are the Fractionation Corrections Correct: Are the Isotopic Shifts for ¹⁴C/¹²C Ratios in Physical Processes and Chemical Reactions Really Twice Those for ¹³C/¹²C?

Southon¹

2011

Radiocarbon

View full text Add to dashboard Cite

ABSTRACT. Conventional radiocarbon calculations correct for isotopic fractionation using an assumed value of 2.0 for the fractionation of 14 C relative to 13 C. In other words, isotopic discrimination in physical and chemical processes is assumed to cause relative shifts in 14 C/ 12 C ratios that are exactly double those of 13 C/ 12 C. This paper analyzes a 1984 experiment that produced a value for the fractionation ratio in photosynthesis of 2.3, which is used to this day by some researchers in the fields of hydrology and speleothem geochemistry. While the value of 2.3 is almost certainly incorrect, theoretical work suggests that the true value may indeed deviate from 2.0, which would have significant implications for 14 C calculations.

show abstract

“…This chain length dependency is related to the inductive electron-donating (+I) effect of terminal methyl (-CH 3 ) groups on adjacent internal methylene (-CH 2 -) positions which increases stiffness in C-H bonds of the latter, thereby favoring slightly greater degrees of 2 H substitution (Hartshorn and Shiner, 1972;Wang et al, 2009c). With increasing chain lengths beyond n-pentane, this effect gradually decreases due to increasing quantities of internal methylene groups (with uniform α o/w values) but it has the capability to produce strikingly similar trends to those observed in thermogenic low molecular weight hydrocarbons.…”

Section: H/ 1 H Signatures In Thermogenic Hydrocarbonsmentioning

confidence: 99%

Hydrogen isotope exchange between n-alkanes and water under hydrothermal conditions

Reeves

Seewald

Sylva

2012

Geochimica et Cosmochimica Acta

View full text Add to dashboard Cite

show abstract

Calculation of H/D carbon-12/carbon-13, and carbon-12/carbon-14 fractionation factors from valence force fields derived for a series of simple organic molecules

Cited by 101 publications

References 9 publications

¹³C kinetic isotope effects and reaction coordinate motions in transition states for S_N2 displacement reactions

¹³C kinetic isotope effects and reaction coordinate motions in transition states for S_N2 displacement reactions

Are the Fractionation Corrections Correct: Are the Isotopic Shifts for ¹⁴C/¹²C Ratios in Physical Processes and Chemical Reactions Really Twice Those for ¹³C/¹²C?

Hydrogen isotope exchange between n-alkanes and water under hydrothermal conditions

Contact Info

Product

Resources

About

Calculation of H/D carbon-12/carbon-13, and carbon-12/carbon-14 fractionation factors from valence force fields derived for a series of simple organic molecules

Cited by 101 publications

References 9 publications

13C kinetic isotope effects and reaction coordinate motions in transition states for SN2 displacement reactions

13C kinetic isotope effects and reaction coordinate motions in transition states for SN2 displacement reactions

Are the Fractionation Corrections Correct: Are the Isotopic Shifts for 14C/12C Ratios in Physical Processes and Chemical Reactions Really Twice Those for 13C/12C?

Hydrogen isotope exchange between n-alkanes and water under hydrothermal conditions

Contact Info

Product

Resources

About

¹³C kinetic isotope effects and reaction coordinate motions in transition states for S_N2 displacement reactions

¹³C kinetic isotope effects and reaction coordinate motions in transition states for S_N2 displacement reactions

Are the Fractionation Corrections Correct: Are the Isotopic Shifts for ¹⁴C/¹²C Ratios in Physical Processes and Chemical Reactions Really Twice Those for ¹³C/¹²C?