The Chemical Imagination at Work inVery Tight Places

Grochala, Wojciech; Hoffmann, Roald; Feng, Ji; Ashcroft, N. W.

doi:10.1002/anie.200602485

Cited by 430 publications

(381 citation statements)

References 173 publications

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“…[35] Thef ormer is the Coulomb interaction between the charge distribution (electrons and nuclei)ofthe molecular solute and the external dielectric medium;t he net interaction is attractive.T he latter term, the Pauli one,m odels the penetration into the repulsive region of intermolecular potentials between the molecule and the solvent, which is how pressure is communicated at the microscopic level. [36] ThePauli repulsion is modeled as aconfining potential for the solutese lectrons.T he confining potential consists of as tep potential barrier located at the boundary of the void molecular cavity.T his potential is zero inside the cavity,s o that Pauli repulsion only exists for the electrons outside the host cavity in PCM. Theheight Z 0 of the barrier (in previous work [33] this was labelled n 0 ;wehave changed the notation to avoid confusion with volume variables V)d epends on the electron density of the external medium [33,37] and reflects the strength of Pauli repulsion by the solvent for the solutes electrons.…”

Section: The Xp-pcm Methods For Studying Reactions Under Pressurementioning

confidence: 99%

The Effect of Pressure on Organic Reactions in Fluids—a New Theoretical Perspective

2017

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This Review brings a new perspective to the study of chemical reactions in compressed fluid media. We begin by reviewing the substantial insight gained from more than 50 years of experimental studies on organic reactions in solution under pressure. These led to a proper estimation of the critical roles of volume of activation (Δ≠V) and reaction volume (ΔV) in understanding pressure effect on rates and equilibria of organic reactions. A recently developed computational method, the XP‐PCM (extreme pressure polarizable continuum model) method, capable of carrying out quantum mechanical calculations of reaction pathways of molecules under pressure, is introduced. A case study of the Diels–Alder cycloaddition of cyclopentadiene with ethylene serves, in pedagogical detail, to describe the methodology. We then apply the XP‐PCM method to a selection of other pericyclic reactions, including the parent Diels–Alder cycloaddition of butadiene with ethylene, electrocyclic ring‐opening of cyclobutene, electrocyclic ring‐closing of Z‐hexatriene, the [1,5]‐H shift in Z‐pentadiene, and the Cope rearrangement. These serve as examples of some of the most common combinations of Δ≠V and ΔV. Interesting phenomena such as a shift in a transition state along a reaction coordinate, a switch of rate‐determining step, and the possible turning of a transition state into a stable minimum are revealed by the calculations. A reaction volume profile, the change in the volume of the reacting molecules as the reaction proceeds, emerges as being useful.

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Section: The Xp-pcm Methods For Studying Reactions Under Pressurementioning

confidence: 99%

The Effect of Pressure on Organic Reactions in Fluids—a New Theoretical Perspective

2017

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“…This is achieved by a progression of squeezing out van der Waals space, rearrangement to more compact isomers of a molecule, and eventually increasing stepwise coordination of all atoms. 22 It is this increasing compactness that led us to think of the trimers, tetramers, and higher oligomers of diborane. We consider in this paper a trimer (B 3 H 9 ), tetramer (B 4 H 12 ), and hexamer (B 6 H 18 ), as well as infinite 1-D chains, all with the stoichiometry 1B:3H.…”

Section: Journal Of the American Chemical Societymentioning

confidence: 99%

BH₃ under Pressure: Leaving the Molecular Diborane Motif

Yao

Hoffmann

2011

J. Am. Chem. Soc.

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Molecular and crystalline structures of (BH 3 ) n have been theoretically studied in the pressure regime from 1 atm to 100 GPa. At lower pressures, crystals of the familiar molecular dimer are the structure of choice. At 1 atm, in addition to the well-characterized β diborane structure, we suggest a new polymorph of B 2 H 6 , fitting the diffraction lines observed in the very first X-ray diffraction investigation of solid diborane, that of Mark and Pohland in 1925. We also find a number of metastable structures for oligomers of BH 3 , including cyclic trimers, tetramers, and hexamers. While the higher oligomers as well as one-dimensional infinite chains (bent at the bridging hydrogens) are less stable than the dimer at ambient pressure, they are stabilized, for reasons of molecular compactness, by application of external pressure. Using periodic DFT calculations, we predict that near 4 GPa a molecular crystal constructed from discrete trimers replaces the β diborane structure as the most stable phase and remains as such until 36 GPa. At higher pressures, a crystal of polymeric, one-dimensional chains is preferred, until at least 100 GPa.

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“…The range of attainable pressures now extends to well over 3 Mbar (3 million atmospheres), laser heating can simultaneously provide temperatures above 5000 K. The behaviour of matter at such harsh conditions is usually drastically different from that known to us from the ambient world. 120 The simplest binary fluorides of Xe, XeF 2 , XeF 4 and XeF 6 have never been exposed to large pressures, largely due to technical problems with strong oxidants inside the diamond anvil cell. What might happen at one or two million atmospheres to, say, XeF 4 ?…”

Section: Pressure As An Independent Variablementioning

confidence: 99%