Coordinated proton tunnelling in a cyclic network of four hydrogen bonds in the solid state

Brougham, Dermot F.; Caciuffo, R.; Horsewill, A.J.

doi:10.1038/16672

Cited by 72 publications

(91 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The concerted mechanism for the dimer was recently confirmed by Rauhut et al [79]. Finally, note that Horsewill et al [80] have reported an intramolecular quasidegenerate quadruple HHHH tunneling process between the OH-groups of solid calix[4]arene, exhibiting temperature-independent rate constants. In a later section the discussion of this process will be pursued.…”

Section: Applicationssupporting

confidence: 49%

“…For comparison, let us compare the methanol data with those obtained by Horsewill et al [80] who have reported an intramolecular quadruple proton transfer in the solid state between the four OH groups of solid calix[4]arene. Almost temperature independent rate constants were observed, which are again indicative of tunneling.…”

Section: The Case Of H-transfer In Pure Methanol and Calix[4]arenementioning

confidence: 94%

“…(c) Kinetic data of the HHHH-transfer in solid p-tert-butyl calix[4]arene reported by Horsewill et al[80] combined with those ofFig. 6.56(a).…”

mentioning

confidence: 99%

See 2 more Smart Citations

Single and Multiple Hydrogen/Deuterium Transfer Reactions in Liquids and Solids

Limbach

2006

Hydrogen‐Transfer Reactions

View full text Add to dashboard Cite

OverviewIn this chapter, Arrhenius curves of selected single and multiple hydrogen transfer reactions for which kinetic data are available over a large temperature range are reviewed. The curves are described by a combination of formal kinetics of reaction networks and the one-dimensional Bell-Limbach tunneling model for each reaction step. The main parameters of this model are the barrier heights and barrier widths of the isotopic reactions, the tunneling masses, the pre-exponential factor and a minimum energy for tunneling to occur. This approach allows one to compare efficiently very different reactions studied in different environments and to prepare the kinetic data for higher-dimensional quantum-mechanical treatments. The first type of reactions discussed is concerned with those where the hydrogen bond geometries of the reacting molecules are well established and where kinetic data of the isotopic reactions are available over a large temperature range. Here, it is possible to study the relation between kinetic isotope effects and chemical structure. Examples are the tautomerism of porphyrin, of the porphyrin anion and related compounds exhibiting intramolecular hydrogen bonds of medium strength, and the solid state tautomerism of pyrazoles and of benzoic acid in cyclic associates. One main result is the finding of pre-exponential factors of the order of kT/h @ 10 13 s -1 , as expected by transition state theory for vanishing activation entropies. The barriers of multiple H-transfers are found to be larger than those of single H-transfers.The second type of reactions discussed refers mostly to liquid state solutions and involves major heavy atom reorganization. Here, equilibria between reactive and nonor less reactive molecular configurations may play a role. Several cases are discussed where the less reactive forms dominate at low or at high temperature, leading to unusual Arrhenius curves. These cases include examples from small molecule solution chemistry like the base-catalyzed intramolecular H-transfer in diaryltriazene, 2-(2¢-hydroxyphenyl)-benzoxazole, 2-hydroxy-phenoxyl radicals as well as an enzymatic system, thermophilic alcohol dehydrogenase. In the latter case, temperature dependent kinetic isotope effects are interpreted in terms of a transition between two regimes with different temperature independent kinetic isotope effects. 135Hydrogen-Transfer Reactions. Edited by

show abstract

Section: Applicationssupporting

confidence: 49%

Section: The Case Of H-transfer In Pure Methanol and Calix[4]arenementioning

confidence: 94%

See 1 more Smart Citation

Single and Multiple Hydrogen/Deuterium Transfer Reactions in Liquids and Solids

Limbach

2006

Hydrogen‐Transfer Reactions

View full text Add to dashboard Cite

show abstract

“…This so-called secondary GIE on the HB distance q 2 was first investigated for molecular crystals using X-ray crystallography by Ubbelohde and Gallagher (Ubbelohde effect). [13] It was only recently, that Benedict et al showed that primary and secondary GIEs in N···HÀN HBs can be obtained as well from solid-state 15 N NMR measurements. [3] In the present Article we give a theoretical account on the GIE of an intramolecular double HB.…”

Section: Introductionmentioning

confidence: 99%

Geometric H/D Isotope Effects and Cooperativity of the Hydrogen Bonds in Porphycene

et al. 2007

View full text Add to dashboard Cite

We investigate the primary, secondary, and vicinal hydrogen/deuterium (H/D) isotope effects on the geometry of the two intramolecular hydrogen bonds in porphycene. Multidimensional potential energy surfaces describing the anharmonic motion in the vicinity of the trans isomer are calculated for the different symmetric (HH/DD) and asymmetric (HD) isotopomers. From the solution of the nuclear Schrödinger equation the ground-state wavefunction is obtained, which is further used to determine the quantum corrections to the classical equilibrium geometries of the hydrogen bonds and thus the geometric isotope effects. In particular, it is found that the hydrogen bonds are cooperative, that is, both expand simultaneously even in the case of an asymmetric isotopic substitution. The theoretical predictions compare favorably with NMR chemical-shift data.

show abstract

“…Inside the bowl there are four hydroxy groups, which form a chiral ring of symmetry C 4 . Horsewill et al [75,76] used NMR relaxometry on crystalline powders to study proton exchange in calix [4]arene and p-tert-butyl calix [4]arene at low temperatures (30-80 and 15-21 K, respectively). They reported clear evidence for concerted quadruple proton transfer.…”

Section: Transfer Of More Than Two Protonsmentioning

confidence: 99%

Multiple Proton Transfer: From Stepwise to Concerted

Smedarchina

Siebrand

Fernández‐Ramos

2006

Hydrogen‐Transfer Reactions

View full text Add to dashboard Cite

It is well recognized that reactions involving the transfer of a proton or hydrogen atom are special in that these particles can tunnel through classically forbidden regions [1]. The wave-like properties also add a new element to reactions in which two or more protons transfer, since under appropriate conditions, they may allow the protons to move as a single particle. In this contribution we review the dynamics of such reactions [2], focusing on double proton transfer for simplicity. In particular, we probe how the motion of one proton influences that of the other and which conditions lead to weak or strong correlation between their motions. Generally speaking, no correlation results in independent transfer and weak correlation in stepwise transfer. Strengthening the correlation will ultimately lead to concerted transfer and may give rise to synchronous transfer if the transferred particles are equivalent.While proton-proton correlation is a unifying concept that allows us to classify and understand the various multiproton transfer mechanisms, it is not a quantity that is easily measured or calculated. In dealing with a specific reaction, one tends to use a simpler approach based on the search for a transition state, i.e. a configuration along the transfer path characterized by a first-order saddle point representing a vibrational force field with one imaginary frequency. More generally, the presence of two mobile particles implies that the potential energy surface contains stationary states with zero, one, or two imaginary frequencies, representing, respectively, a stable intermediate, a transition state, and a state with a secondorder saddle point.A stable intermediate roughly halfway along the trajectory implies barriers separating it from the equilibrium configurations. Such a potential favors stepwise transfer under conditions where the intermediate is thermally accessible. This basically reduces the dynamics to that appropriate for single proton transfer, but leaves open the question of how to deal with transfer at low temperature. A barrier corresponding to a single transition state, similar to that observed for single proton transfer, implies concerted transfer of the two protons. This again can Hydrogen-Transfer Reactions. Edited by be treated by the methods developed for single proton dynamics [1,3]. However, if, instead, this barrier corresponds to a second-order saddle point, it represents concerted motion along two proton coordinates. This situation does not immediately reveal the nature of the corresponding transfer process, but it drives home the point that the presence of two mobile protons allows at least two transfer mechanisms. On a potential energy surface with more than one saddle point, there will in general be multiple pathways along which the potential has a doubleminimum profile. To analyze the transfer dynamics governed by such a potential, we need an approach that goes beyond the question whether the transfer is concerted or stepwise.To elucidate the effect of proton-proton correlation...

show abstract

Coordinated proton tunnelling in a cyclic network of four hydrogen bonds in the solid state

Cited by 72 publications

References 12 publications

Single and Multiple Hydrogen/Deuterium Transfer Reactions in Liquids and Solids

Single and Multiple Hydrogen/Deuterium Transfer Reactions in Liquids and Solids

Geometric H/D Isotope Effects and Cooperativity of the Hydrogen Bonds in Porphycene

Multiple Proton Transfer: From Stepwise to Concerted

Contact Info

Product

Resources

About