Stepwise two-proton transfer within the formamidine dimer. A theoretical study using Ab initio calculations

Svensson, Peder; Bergman, Nils-Åke; Ahlberg, Per

doi:10.1039/c39900000082

Cited by 11 publications

(17 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The difference in energy between R and I (Δ E ) and the barrier heights (Δ E* ) are listed in Table . They depend very much on the levels of quantum mechanical calculations and the inclusion of electron correlation. , The Δ E values at the HF/6-31+G(d,p) and B3LYP/6-31+G(d,p) levels are 22.85 and 19.08 kcal mol -1 , respectively. The Δ E* values at the HF/6-31+G(d,p), B3LYP/6-31+G(d,p), and MP2(full)/6-31G(d,p) levels are 32.62, 22.52, and 24.93 kcal mol -1 , respectively.…”

Section: Resultsmentioning

confidence: 99%

“…Because of the light mass of the transferred atom, the importance of tunneling in proton transfer reactions has been discussed for many years . Recently many theoretical studies with ab initio quantum chemical methods at various levels have been carried out to predict the structures of hydrogen-bonded dimers and the potential energy surfaces (PESs) for various double proton transfer processes. − It has been shown that the height and shape of the PES depend strongly on the theoretical level of calculation, the size of the basis set, and the inclusion of correlation energy. − ,, ,15 Since most of the earlier studies have focused on the geometrical change on dimerization and the energetic stabilization due to the hydrogen bonds in the dimer, the dynamic features of the double proton transfer, such as tunneling and the effect of isotopic substitution, are not yet very well understood. To study the dynamics of such systems, detailed information about the potential energy surface near the TS and the critical configuration is needed.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Dynamics and Kinetic Isotope Effects for the Intramolecular Double Proton Transfer in Oxalamidine Using Direct Semiempirical Dynamics Calculation

Kim

Hwang

1999

J. Am. Chem. Soc.

View full text Add to dashboard Cite

We have carried out direct semiempirical dynamics calculations for the double proton transfer in oxalamidine using variational transition state theory with multidimensional semiclassical tunneling approximations. This double proton transfer occurs stepwise, with an intermediate. The energy of the intermediate relative to the reactant and the barrier height have been calculated at the G2* level of theory, which yields 20.8 and 25.1 kcal mol-1, respectively. A quantum mechanical potential energy surface has been constructed using the AM1 Hamiltonian with specific reaction parameters (AM1-SRP) which are obtained by adjusting the standard AM1 parameters to reproduce the energetics given by the G2* level of theory. The minimum energy path has been calculated on the AM1-SRP potential energy surface, and other characteristics of the surface were calculated as needed. The hydrogenic motion is separated from the heavy atom motion along the reaction coordinate. The proton hops about 0.32 Å by tunneling, but heavy atoms do not move much while tunneling occurs. Tunneling reduces the adiabatic energy barrier by 0.67 kcal mol-1. Rate constants and kinetic isotope effects (KIEs) have been determined experimentally in methylcyclohexane and acetonitrile solutions for a bicyclic oxalamidine. The calculated KIEs agree very well with the experimental values. The calculated activation energy is about 35% higher than the measured value. The equilibrium isotope effects and the quasiclassical secondary KIEs reveal that proton transfer and the change in the force constants are asynchronous. Although the geometric parameters for the transition state (TS) are closer to those for the intermediate than those for the reactant (TS is late geometrically), the force constants are more similar to those of the reactant (TS is early in terms of force constants). The change in force constants is a nonlinear function of the geometric parameters, and depends on the position.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dynamics and Kinetic Isotope Effects for the Intramolecular Double Proton Transfer in Oxalamidine Using Direct Semiempirical Dynamics Calculation

Kim

Hwang

1999

J. Am. Chem. Soc.

View full text Add to dashboard Cite

show abstract

“…In addition to serving as a model for hydrogen transfer reactions in bases of nucleic acids, formamidine has been extensively studied theoretically since it also forms homodimers and hydrogen bonds with water. Intramolecular and intermolecular hydrogen transfers have been studied theoretically for various formamidine systems. ,,− Proton transfers in formamidine dimer can also be considered a prototype of multiproton transfer. They can also provide information about hydrogen bonding, as well as the proton relay mechanism in enzymes.…”

Section: Introductionmentioning

confidence: 99%

“…Forming a homodimer can also facilitate the tautomerization reaction, and therefore we have studied the double proton transfer in the dimer-assisted as well as the water-assisted tautomerization in the gas phase and in solution. Since electron correlation plays an important role in determining the characteristics of the PES for the proton transfer reaction in the gas phase, ,,− it is necessary to consider the correlation effect in solution too. The density functional theory has been successfully applied to the proton transfer reactions and it agrees well with other methods including high-level electron correlation.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of the Double Proton Transfer in Hydrogen-Bonded Complexes in the Gas Phase and in Solution: Prototropic Tautomerization of Formamide

et al. 1999

View full text Add to dashboard Cite

Double proton transfers in the prototropic tautomerism of formamide dimer and monohydrated formamide in the gas phase and in solution have been studied as prototypes of multiple proton transfer. The potential energy surface (PES) for the double proton transfer was studied using ab initio quantum mechanical methods, and the solvent effect on the PES was included using the self-consistent reaction field model. In the gas phase, the transition state for the double proton transfer in formamide dimer has C s symmetry, when the Hartree−Fock (HF) level of theory is used. When the MP2 and B3LYP levels of theory are used to consider electron correlation, the transition state has C 2 h symmetry. The double proton transfer occurs concertedly and synchronously. The H bonds in homodimers are stronger than in monohydrated complexes, and the H bonds with formamidic acid are stronger than with formamide. The changes in the H-bond strengths and distances were also calculated as the dielectric constant was increased. The barrier height depends very much on the electron correlation, and the reaction energies of the tautomerization are very sensitive to the size of basis sets. The potential energy barrier for the tautomerization is lowered about 30 kcal mol-1 in the gas phase by forming hydrogen-bonded dimer. The dimer-assisted tautomerization is kinetically more favorable, but thermodynamically less favorable, than the water-assisted. The tautomerization energies and the potential energy barriers are increased as the dielectric constant is increased both for the water-assisted and for the dimer-assisted reactions, which imply that the tautomerization of formamide becomes less favorable in a polar solvent.

show abstract

“…At this level the two hydrons are transferred concertedly and synchrono~sly.~ It was later shown that with more extended basis sets the minimum energy path for the two-hydron transfer in this system corresponds to a stepwise mechanism. 5 In the present communication we present some data on the formic acid dimer system. This system shows a concerted and synchronous transfer of the two hydrons at all computational levels that have been used.…”

mentioning

confidence: 94%

Concerted synchronous two-hydron transfer within the formic acid dimer. A kinetic isotope effect study using ab initio calculations

Svensson¹,

Bergman²,

Ahlberg³

1990

J. Chem. Soc., Chem. Commun.

Self Cite

View full text Add to dashboard Cite

show abstract

Stepwise two-proton transfer within the formamidine dimer. A theoretical study using Ab initio calculations

Abstract: Ab initio calculations at the VDZ and VDZ + P levels of theory of the two-proton transfer reaction within an isolated formamidine dimer give transition states with low symmetry, and with 6-31G" basis sets indicate stepwise two-proton transfers even in the absence of solvent.

Cited by 11 publications

References 3 publications

Dynamics and Kinetic Isotope Effects for the Intramolecular Double Proton Transfer in Oxalamidine Using Direct Semiempirical Dynamics Calculation

Dynamics and Kinetic Isotope Effects for the Intramolecular Double Proton Transfer in Oxalamidine Using Direct Semiempirical Dynamics Calculation

Theoretical Study of the Double Proton Transfer in Hydrogen-Bonded Complexes in the Gas Phase and in Solution: Prototropic Tautomerization of Formamide

Concerted synchronous two-hydron transfer within the formic acid dimer. A kinetic isotope effect study using ab initio calculations

Contact Info

Product

Resources

About