Instanton theory of tunneling in molecules with asymmetric isotopic substitutions

Jahr, Elena; Laude, Gabriel; Richardson, Jeremy O.

doi:10.1063/5.0021831

Cited by 18 publications

(45 citation statements)

References 94 publications

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“…Symmetric parents for other well investigated structural families with respect to (partial) localization by chemical or isotopic symmetry breaking include porphycen (tunneling splitting of 4.4 cm

) [ 37 , 38 , 39 , 40 , 41 ], malonaldehyde (21.6 cm

) [ 4 , 7 , 14 ] and 9-hydroxyphenalenone (69 cm

) [ 3 , 42 , 43 , 44 , 45 ].…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Delocalization in an Asymmetric Biomolecule: The Curious Case of Alpha-Fenchol

et al. 2021

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Rotational microwave jet spectroscopy studies of the monoterpenol α-fenchol have so far failed to identify its second most stable torsional conformer, despite computational predictions that it is only very slightly higher in energy than the global minimum. Vibrational FTIR and Raman jet spectroscopy investigations reveal unusually complex OH and OD stretching spectra compared to other alcohols. Via modeling of the torsional states, observed spectral splittings are explained by delocalization of the hydroxy hydrogen atom through quantum tunneling between the two non-equivalent but accidentally near-degenerate conformers separated by a low and narrow barrier. The energy differences between the torsional states are determined to be only 16(1) and 7(1) cm−1hc for the protiated and deuterated alcohol, respectively, which further shrink to 9(1) and 3(1) cm−1hc upon OH or OD stretch excitation. Comparisons are made with the more strongly asymmetric monoterpenols borneol and isopinocampheol as well as with the symmetric, rapidly tunneling propargyl alcohol. In addition, the third—in contrast localized—torsional conformer and the most stable dimer are assigned for α-fenchol, as well as the two most stable dimers for propargyl alcohol.

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) [ 37 , 38 , 39 , 40 , 41 ], malonaldehyde (21.6 cm

) [ 4 , 7 , 14 ] and 9-hydroxyphenalenone (69 cm

) [ 3 , 42 , 43 , 44 , 45 ].…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Delocalization in an Asymmetric Biomolecule: The Curious Case of Alpha-Fenchol

et al. 2021

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“…For a molecular cluster, in general, different configurations are distinguishable and acquire different energies. In asymmetric environments, the delocalization of the protons by tunneling usually competes with the localization of the protons by the environment, and the latter usually wins, with only a few exceptions reported so far [20] . As a result, it is rare to observe proton tunneling in molecular complexes.…”

Section: Figurementioning

confidence: 99%

Double Proton Transfer Across a Table: The Formic Acid Dimer–Fluorobenzene Complex

Tikhonov

Schnell

2021

Angewandte Chemie

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Proton transfer via tunneling is a fundamental quantum-mechanical phenomenon. We report rotational spectroscopy measurements of this process in the complex of the formic acid dimer with fluorobenzene. The assignment of the spectrum indicates that this complex exists in the form of a p-p stacked structure. Each rotational transition of the parent isotopologue exhibits splitting. Isotopic substitution experiments show that the spectral splitting results from doubleproton transfer tunneling in the formic acid dimer. Presence of fluorobenzene as a neighboring molecule does not quench the double proton transfer in the formic acid dimer but decreases its tunneling splitting from 341(3) MHz to 267.608(1) MHz. Calculations suggest that the presence of the weakly bounded fluorobenzene does not influence the activation energy of the proton transfer. The fluorobenzene is reoriented with respect to the formic acid dimer during the course of the reaction, slowing down the proton transfer motion.

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“…The description of tunneling in such slightly asymmetric double-minimum potentials continues to draw interest from the theoretical side. [6][7][8][9][10][11][12][13][14] Known experimental splittings for hydrogen atom tunneling span a range of more than eight orders of magnitudes, with most of them being (far) smaller than 1 cm −1 hc ( ≈ 0.01 kJ mol −1 ) [15]. For this reason, localization is the typical, but not the strict, outcome from symmetry breaking by chemical [3,[16][17][18][19] or isotopic [4,5,[20][21][22][23][24][25][26][27][28] substitution, internal rotation of molecular groups [6,16,20,24,29], or from environmental influences such as solvation [16,30], matrix embedding [3,31,32] or crystallization [33].…”

Section: Introductionmentioning

confidence: 99%

“…Symmetric parents for other well investigated structural families in respect to (partial) localization by chemical or isotopic symmetry breaking include porphycen (tunneling splitting of 4.4 cm −1 hc) [37][38][39][40][41], malonaldehyde (21.6 cm −1 hc) [4,7,14] and 9-hydroxyphenalenone (69 cm −1 hc) [3,[42][43][44][45].…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Delocalization in an Asymmetric Biomolecule: The Curious Case of alpha-Fenchol

Medel¹,

Springborn²,

Crittenden³

et al. 2021

Preprint

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Rotational microwave jet spectroscopy studies of the monoterpenol α-fenchol have so far failed to identify its second expected torsional conformer, despite computational predictions that it is only very slightly higher in energy than the most stable conformer. Vibrational FTIR and Raman jet spectroscopy investigations reveal unusually complex OH and OD stretching spectra compared to other alcohols. Via modelling of the torsional states, observed spectral splittings are explained by delocalization of the hydroxy hydrogen atom through quantum tunneling between the two non-equivalent but accidentally near-degenerate conformers separated by a low and narrow barrier. The energy differences between the torsional states are determined to be only 16(1) and 7(1) cm$^{−1}hc$ for the protiated and deuterated alcohol, respectively, which further shrink to 9(1) and 3(1) cm$^{−1}hc$ upon OH or OD stretch excitation. Comparisons are made with the more strongly asymmetric monoterpenols borneol and isopinocampheol as well as with the symmetric, rapidly tunneling propargyl alcohol. Assigned are also for α-fenchol the third – in contrast localized – torsional conformer and the most stable dimer, as well as for propargyl alcohol the two most stable dimers.

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Instanton theory of tunneling in molecules with asymmetric isotopic substitutions

Cited by 18 publications

References 94 publications

Hydrogen Delocalization in an Asymmetric Biomolecule: The Curious Case of Alpha-Fenchol

Hydrogen Delocalization in an Asymmetric Biomolecule: The Curious Case of Alpha-Fenchol

Double Proton Transfer Across a Table: The Formic Acid Dimer–Fluorobenzene Complex

Hydrogen Delocalization in an Asymmetric Biomolecule: The Curious Case of alpha-Fenchol

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