A two-dimensional potential function for bent hydrogen bonded systems. II-6-hydroxy-2-formylfulvene

Tayyari, Sayyed Faramarz; Zahedi-Tabrizi, Mansoureh; Rahemi, H.; Mirshahi, Hassan-Ali; Emampour, Jalal S.; Rajabi, Mojtaba; Milani-Nejad, Fereydoon

doi:10.1016/j.theochem.2005.06.010

Cited by 13 publications

(10 citation statements)

References 15 publications

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“…The absence of discernible tunneling signatures, combined with the relative intensities of hot-band transitions, placed a lower limit of 150 cm –1 on the dynamical bifurcation of vibrationless HFF. Theoretical treatments of proton-transfer dynamics conducted on potential-energy surfaces of reduced dimensionality by Millefiori and Alparone and by Tayyari et al reinforced this experimental estimate, reporting Δ 0 X̃ parameters of 142 and 181 cm –1 , respectively, where the latter dropped to 43 cm –1 upon deuteration. Recent NMR probes of chemical shifts and isotopic perturbations, , as well as earlier measurements of deuterium electric-field gradients and quadrupole coupling constants, have been interpreted in terms of facile exchange processes between asymmetric forms that might reflect local disorder arising from differential solvation effects. , Prior spectroscopic investigations of electronically excited HFF appear to have been limited to solution-phase ultraviolet absorption traces of low resolution. , …”

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confidence: 90%

Spectral Signatures of Proton-Transfer Dynamics at the Cusp of Low-Barrier Hydrogen Bonding

Vealey

Foguel

Vaccaro

2018

J. Phys. Chem. Lett.

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Despite their importance in diverse chemical and biochemical processes, low-barrier hydrogen bonds remain elusive targets to classify and interpret spectroscopically. Here the correlated nature of hydrogen bonding and proton transfer in the low-barrier regime has been probed for the ground and excited electronic states of 6-hydroxy-2-formylfulvene by acquiring jet-cooled fluorescence spectra of the parent and monodeuterated isotopologs. While excited-state profiles reveal regular vibronic patterns devoid of obvious dynamical signatures, their ground-state counterparts display a radically altered energy landscape characterized by spectral bifurcations comparable in magnitude to typical vibrational spacings (>100 cm). Quantitative analyses yield unusual deuterium kinetic isotope effects that straddle limiting values attributed to above-barrier vibration and below-barrier tunneling of the proton adjoining donor/acceptor sites. Our findings provide compelling experimental evidence for ultrafast hydron-migration events commensurate with the onset of low-barrier hydrogen bonding and afford a trenchant glimpse of molecular phenomena taking place at the "tipping point" between disparate dynamical regimes.

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confidence: 90%

Spectral Signatures of Proton-Transfer Dynamics at the Cusp of Low-Barrier Hydrogen Bonding

Vealey

Foguel

Vaccaro

2018

J. Phys. Chem. Lett.

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“…1a). The IHB proton transfer in the enol form of b-diketones has been extensively investigated from both experimental [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and theoretical [22][23][24][25][26][27][28][29][30][31][32][33][34] points of view.…”

Section: Introductionmentioning

confidence: 99%

“…Tayyari et al 24 applied two-dimensional symmetric double minimum potential for the hydrogen transfer in the bent IHB system and correctly obtained the proton tunneling frequencies of MA 24 and a-nitromalonaldehyde (NO 2 -MA). 25 Such a model was also successfully applied to the IHB of 6-hydroxy-2-formylfulvene, 34 a nearly linear hydrogen bonded system.…”

Section: Introductionmentioning

confidence: 99%

Proton transfer in acetylacetone and its α-halo derivatives

Dolati

Tayyari

Vakili

et al. 2016

Phys. Chem. Chem. Phys.

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A two-dimensional potential energy surface was utilized to treat the proton transfer in acetylacetone (AA) and its α-halo derivatives: α-fluoro-(FAA), α-chloro-(ClAA), and α-bromo-acetylacetone (BrAA). This potential energy function, which couples O-H stretching and in-plane bending vibrations, was acquired through ab initio calculations for a fixed skeleton geometry. The resulting potential energy surfaces were then used to calculate the proton tunneling frequencies and proton transfer barrier heights. The barrier heights (the energy difference between the saddle point and the minima) calculated at the MP2/6-31G(2d,p) level of theory for proton transfers in AA, FAA, ClAA, and BrAA are 7.2, 9.4, 6.3, and 5.9 kcal mol(-1), respectively. The theoretically predicted proton transfer barrier heights exhibit excellent linear correlations with geometrical, electronic structural, and topological parameters evaluated by the atoms-in-molecule (AIM) and natural bond orbital (NBO) analyses.

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“…These authors also examined HFF proton-transfer dynamics quantitatively under the assumption of a one-dimensional reaction coordinate, leading to a predicted tunneling splitting for the zero-point (v = 0) level of Δ 0 X̃ = 142 cm –1 that displayed a strong dependence on model chemistry yet was in reasonable accord with the findings of microwave spectroscopy . Tayyari et al extended this work by creating two-dimensional MP2/6-31G** and B3LYP/6-311++G** reaction surfaces built upon O–H stretching and O–H···O bending degrees of freedom (with all other internal coordinates remaining fixed at optimized equilibrium values). Numerical diagonalization of the resulting MP2/6-31G** Hamiltonian produced a vibrationless bifurcation of Δ 0 X̃ = 181 ± 14 cm –1 that was reduced to 43 ± 9 cm –1 upon deuteration of the shuttling hydron (listed “error bars” indicate the spread of predictions made with different potential-energy cutoffs), reflecting the need to surmount an impediment of 26.5–27.2 kJ/mol (2215–2274 cm –1 ) to reach the transition-state configuration.…”

Section: Introductionmentioning

confidence: 91%

“…These authors also examined HFF protontransfer dynamics quantitatively under the assumption of a onedimensional reaction coordinate, leading to a predicted tunneling splitting for the zero-point (v = 0) level of Δ 0 X ̃= 142 cm −1 that displayed a strong dependence on model chemistry yet was in reasonable accord with the findings of microwave spectroscopy. 45 Tayyari et al 59 In contrast to the X ̃1A 1 ground state, very little experimental and theoretical information has been reported for the electronically excited manifolds of HFF. As part of a study to elucidate the extent of nonclassical aromaticity in the 6-aminofulvene-2aldimine family, Muller-Westerhoff 61 published a low-resolution UV−vis absorption spectrum of HFF (the oxygen analogue of 6aminofulvene-2-aldimine) solvated in n-hexane, noting the appearance of three distinct bands peaking at λ max values of 393, 317, and 243 nm.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen-Bonding Motifs and Proton-Transfer Dynamics in Electronically Excited 6-Hydroxy-2-formylfulvene

2019

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To elucidate low-barrier hydrogen-bonding (LBHBing) motifs and their ramifications for hydron-migration dynamics, the A ̃1B 2 −X ̃1A 1 (π* ← π) absorption system of 6-hydroxy-2-formylfulvene (HFF) and its monodeuterated isotopolog (HFFd) has been probed under free-jet expansion conditions through synergistic application of fluorescence-based laser spectroscopy and quantum-chemical calculations. Neither the donor−acceptor distance nor the proton-transfer barrier is predicted to change markedly between the X ̃1A 1 and A ̃1B 2 manifolds, yet a radical alteration in the nature of the reaction coordinate, whereby the planar (C 2v ) transition-state configuration of the former is supplanted by a notably aplanar (C 2 ) form in the latter, is suggested to take place following π* ← π electron promotion (owing, in part, to attendant rearrangements of πelectron conjugation about the molecular framework). In contrast to the strongly perturbed vibrational landscape (commensurate with LBHBing) reported for the X ̃1A 1 potential surface, the present measurements have revealed surprisingly regular patterns of A ̃1B 2 vibronic structure which are devoid of obvious band shifts/splittings that would be indicative of efficient proton-transfer processes. Detailed analyses enabled a total of 41 (6) and 28 (5) excited-state vibrational levels (fundamentals) to be assigned for HFF and HFF-d, with extensive activity found for modes involving displacement of the seven-membered chelate ring that harbors the O−H•••O reaction center. Quantitative simulations of partially resolved rotational contours for the HFF origin band showed the transition dipole moment to possess hybrid type-a/b character, thereby allowing the tunneling-induced bifurcation of the vibrationless A ̃1B 2 level to be extracted, Δ 0 A ̃= 0.119(11) cm −1 . This represents an enormous (>1000-fold) decrease over the analogous ground-state metric and implies a pronounced quenching of excited-state hydron migration, in keeping with the kinematic penalties that would be exacted by requisite heavy-atom motion along a putatively aplanar reaction coordinate.

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A two-dimensional potential function for bent hydrogen bonded systems. II-6-hydroxy-2-formylfulvene

Cited by 13 publications

References 15 publications

Spectral Signatures of Proton-Transfer Dynamics at the Cusp of Low-Barrier Hydrogen Bonding

Spectral Signatures of Proton-Transfer Dynamics at the Cusp of Low-Barrier Hydrogen Bonding

Proton transfer in acetylacetone and its α-halo derivatives

Hydrogen-Bonding Motifs and Proton-Transfer Dynamics in Electronically Excited 6-Hydroxy-2-formylfulvene

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