Unusual long-range spin-spin coupling in fluorinated polyenes: A mechanistic analysis

Gräfenstein, Jürgen; Cremer, Dieter

doi:10.1063/1.2787001

Cited by 10 publications

(19 citation statements)

References 59 publications

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“…For this J-coupling the SD term is as large as the FC one. This is in line with previous findings. − As will be shown in section 3.4 this pattern is due to the contributions of fluorine LPs. In all other J-couplings of 1,2-difluoroethene the contribution of the FC mechanism is by far the largest one.…”

Section: Resultssupporting

confidence: 92%

Analysis of Electron Correlation Effects and Contributions of NMR J-Couplings from Occupied Localized Molecular Orbitals

Zarycz

Aucar

2012

J. Phys. Chem. A

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NMR J-coupling calculations at the second-order of polarization propagator approach, SOPPA, are among the most reliable. They include a high percentage of the total electron correlation effects in saturated and unsaturated molecular systems. Furthermore, J-couplings are quite sensitive to the whole electronic molecular framework. We present in this article the first study of all three response mechanisms, Fermi contact, FC, spin-dipolar, SD and paramagnetic spin-orbital, PSO, for J-couplings with occupied localized molecular orbitals at the SOPPA level of approach. Even though SOPPA results are not invariant under unitary transformations, the difference between results obtained with canonical and localized molecular orbitals, LMOs, are small enough to permit its application with confidence. The following small-size saturated and unsaturated compounds were analyzed: CH(4), CH(3)F, C(2)H(6), NH(3), C(2)H(4), CH(2)NH, H(2)C═CHF, and FHC═CHF. The local character of the FC mechanism that appears in J-couplings of these molecular models is shown through the analysis of contributions from LMOs. The importance of including the electron correlation on the engaged bonding orbitals for one-bond couplings is emphasized. Almost all electron correlation effects are included in such orbitals. Interesting findings were the large contributions by s-type LMOs to the C-H and C-C J-couplings; they are responsible for the variation of (1)J(C-C) when going from ethane to ethene and to 1,2-difluoroethene. The previously proposed hyperconjugative transfer mechanism has been tested. Among other tests we found the difference anti-syn of one-bond (1)J(C-H) in imine as due to both the corresponding σ(C-H) and the lone-pair, LP, contribution. Geminal and vicinal J-couplings were also analyzed. Our findings are in accord with a previous work by Pople and Bothner-by, who considered results taken from calculations or empirical data. For all geminal couplings the pattern of J-couplings, like the change of sign, is originated in the main bondings that participate in the coupling pathways. The finding of asymmetric contributions of LP to vicinal H-H couplings in imine is highlighted. The analysis of J-couplings by contributions from LMOs to the noncontact mechanisms, SD and PSO, show that the π electronic framework makes both terms grow in the specific case of the model compounds studied here. The PSO mechanism is more efficient when a σ bond is vicinal to a π bond. We found in this way an efficient and powerful scheme to get a deeper insight on the electronic molecular framework on which J-couplings are transmitted.

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Section: Resultssupporting

confidence: 92%

Analysis of Electron Correlation Effects and Contributions of NMR J-Couplings from Occupied Localized Molecular Orbitals

Zarycz

Aucar

2012

J. Phys. Chem. A

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“…The p z -type of LP(F) and the σ (C-F) give together a contribution of 21.60 Hz out of the total 26.75 Hz. This is in line with a previous work published by Gräfenstein and Cremer,25 though our procedure is more straightforward in obtaining similar physical insights.…”

Section: Transmission Of the Sd Nucleus-electron Interacting Mechasupporting

confidence: 91%

“…They developed the J decomposition into orbital contributions with the help of orbital currents and partial spin polarization (JOC-PSP) method. 22 They were able to learn on the π -character of a C-C bond by studying non-contact terms, 23 the origin of large SD components of J-couplings in fluorinated polyenes, 24,25 by the π -mechanism involved in J-couplings in polyenes previously studied by Provasi et al 26 The JOC-PSP method makes it possible to analyze the four J-coupling transmission mechanisms in terms of orbital contributions in the framework of DFT. 4 Sauer and Provasi had also applied LMOs in the analysis of isotope effects on NMR J-couplings 27,28 Their scheme is actually an ab initio implementation of the CLOPPA approach in the DALTON code 29 at RPA and TD-DFT level of theory.…”

Section: Introductionmentioning

confidence: 99%

The analysis of NMR J-couplings of saturated and unsaturated compounds by the localized second order polarization propagator approach method

Zarycz

Aucar

2012

The Journal of Chemical Physics

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Calculations of NMR J-coupling with polarization propagators are not invariant under unitary transformations at second order level of approach, second order polarization propagator approach (SOPPA). They are only invariant at first order or random phase level of approach (RPA). We performed "localized" SOPPA (Loc-SOPPA), calculations of J-couplings applying two different schemes for the localization of molecular orbitals(LMO): Foster-Boys and Pipek-Mezey. We show here that results of such Loc-SOPPA calculations are different though not much: they are less than 6% different in the worst case. Therefore it is possible to apply them with confidence in the analysis of the transmission of different coupling mechanisms within the molecule. We are able now to get reliable information on what LMOs are the most important (and so which are not important) for a given J-coupling in a molecule. This information can then be used for selecting which are the paths that should be described with the highest possible accuracy for that J-coupling calculation. A few unsaturated compounds are analyzed: ethene, trans-difluoroethene or DiF-ethene, and imine. It is shown that different lone pairs (of p(z) or p(x/y) type) are responsible for the vicinal F-F J-coupling in DiF-ethene; and also the fact that the main LP contributor is not the same for the fermi contact and the spin-dipolar mechanisms. We also studied phosphorous containing compounds such as phosphine and cis-propylene phosphine. In both cases the analysis of the main LMO contributing to one-bond P-H coupling and through-space P-C coupling were performed. The above mentioned unsaturated molecular systems have quasiinstability problems that arise at RPA level of approach. We show here that they are mostly originated in the antibonding π∗ LMO, corresponding to the C=C or C=N double bonds. We performed the analysis of the origin of quasiinstabilities for the SD mechanism. The contribution of each kind of excitation terms to SOPPA calculations were considered, meaning the main contributions by single and double excitations. It is shown that one can get more than 97% of the total electron correlation contribution when including terms that mainly contain single excitations (though double-excitation matrix elements should still be calculated).

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“…From the asymptotic behaviour of the calculated couplings in the 1,n-difluoropolyynes, they estimated couplings of J(F-F) % 3.6 Hz over 13 bonds or a distance of $1.6 nm and of J(F-F) % 1.8 Hz over 15 bonds or a distance of $2 nm. New studies have confirmed these findings [61]. A recent study of the intramolecular proton transfer mechanism in ortho-hydroxyaryl substituted Schiff bases with the B3LYP-DFT and SOPPA schemes shows that one can predict the dependence of both parameters, 1 J( 15 N 1 H) and ( 15 N), with the distance d(NH) on OH and NH tautomers [36].…”

Section: As Observed In Equationsmentioning

confidence: 72%

Polarization propagators: A powerful theoretical tool for a deeper understanding of NMR spectroscopic parameters

Aucar

Romero

Maldonado

2010

International Reviews in Physical Chemistry

106

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Unusual long-range spin-spin coupling in fluorinated polyenes: A mechanistic analysis

Cited by 10 publications

References 59 publications

Analysis of Electron Correlation Effects and Contributions of NMR J-Couplings from Occupied Localized Molecular Orbitals

Analysis of Electron Correlation Effects and Contributions of NMR J-Couplings from Occupied Localized Molecular Orbitals

The analysis of NMR J-couplings of saturated and unsaturated compounds by the localized second order polarization propagator approach method

Polarization propagators: A powerful theoretical tool for a deeper understanding of NMR spectroscopic parameters

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