Correlation of nmr Chemical Shifts with Hammett σ Values and Analogous Parameters

Ewing, David F.

doi:10.1007/978-1-4615-8831-3_8

Cited by 32 publications

(19 citation statements)

References 149 publications

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“…The correlation of experimental observables with the various Hammett-type relations that have been developed over the years has helped to put these ideas on a more quantitative (though still largely empirical) basis. [4][5][6][7][8] In so doing, the physical-organic community in particular has been able to develop tremendous physical and mechanistic insights into the cause-and-effect relationship between charge polarization and chemical reactivity. [9][10][11][12][13] A comparable level of understanding of the effect of spin on chemical reactivity suffers in part from the lack of a similarly intuitive counterpart to electronegativity for spin polarization.…”

Section: Introductionmentioning

confidence: 99%

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Fehir

McCusker

2009

J. Phys. Chem. A

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We have carried out a theoretical study of a series of para-substituted phenoxy radicals in an effort to understand the factors influencing spin and charge density distribution in open-shell systems. The calculations reveal that the distribution of spin and charge are not correlated: cases were found for which spin and charge move together, whereas for other substituents the two quantities exhibit spatially distinct intramolecular polarizations. Charge density variations across the series were found to correlate well with both the Hammett (σ p ) and Hammett-Brown (σ p + ) constants for each substituent, indicating that inductive and/or resonance effects are primarily responsible for the polarization of charge within the molecule. In contrast, the distribution of unpaired spin density could not be adequately accounted for using any of the typical Hammett-type spin delocalization constants cited in the literature. We uncovered an empirical correlation between the polarization of spin density and the R-HOMO-R-LUMO gap of the substituted phenoxy radicals: this led to the development of a simple model based on a three-electron, two-orbital bonding scheme in which mixing between the HOMO of the substituent and the SOMO of the phenoxy moiety serves to define the nature and extent of unpaired spin polarization throughout the molecule. This analysis yielded a correlation coefficient of r > 0.97 for the 15 substituents examined in the study; spin polarization effects in compounds that exhibited the greatest deviation from this correlation could also be readily explained within the context of the model. The underlying reason for the ability to differentially polarize spin and charge likely stems from the fact that net unpaired spin density is completely carried by the unpaired electron (and thus tracks the spatial characteristics of the SOMO), whereas charge density reflects the behavior of all of the electrons of the system. These results could have implications in the field of molecular magnetism, suggesting a means for synthetically tuning the magnitude of intramolecular exchange interactions, as well as providing guidance for the design of catalysts for radical-radical coupling reactions.

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Section: Introductionmentioning

confidence: 99%

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Fehir

McCusker

2009

J. Phys. Chem. A

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“…The chart illustrates an insignificant effect of the properties of the phosphine ligand on the catalytic activity of the complexes. The order of increasing activities of the activated species, i.e., 8 (PPh 3 ) < 10 P(C 6 H 4 Me-4) 3 < 1a (PCy 3 ) < 9 P(C 6 H 4 CF 3 -4) 3 does not correlate with decreasing σ-donor ability of the phosphine ligands (represented by Hammet constant) [12–13]. The highest activity was indeed observed for complex 9 containing the weakest σ-donor and potentially most easily dissociating ligand P(C 6 H 4 CF 3 -4) 3 .…”

Section: Resultsmentioning

confidence: 99%

New aryloxybenzylidene ruthenium chelates – synthesis, reactivity and catalytic performance in ROMP

Żak¹,

Rogalski²,

Majchrzak³

et al. 2015

Beilstein J. Org. Chem.

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SummaryNew phenoxybenzylidene ruthenium chelates were synthesised from the second generation Grubbs catalysts bearing a triphenylphosphine ligand (or its para-substituted analogues) by metathesis exchange with substituted 2-vinylphenols. The complexes behave like a latent catalyst and are characterized by an improved catalytic behaviour as compared to that of the known analogues, i.e., they exhibit high catalytic inactivity in their dormant forms and a profound increase in activity after activation with HCl. The strong electronic influence of substituents in the chelating ligand on the catalytic activity was demonstrated. The catalytic properties were tested in ROMP of cyclooctadien (COD) and a single selected norbornene derivative.

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“…3). The smaller enantioselectivity of m-substituted compounds (as compared to p-substituted) could also be explained in terms of their smaller electron donating power (p-F − = 0.15, m-F − = 0.34; p-Me − = −0.14, m-Me − = −0.06; p-OMe − = −0.28, m-OMe − = 0.10 [21][22][23] ). It should, however, be noted that no straightforward relationship was found for the set of p-and msubstituted compounds.…”

Section: Resultsmentioning

confidence: 99%

“…Relationship between enantioselectivities and Hammet constants[21][22][23] for p-substituted compounds 1, 6, 7, 8, and 11.…”

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confidence: 99%

Enantioselectivity of 3‐amino‐2‐oxazolidinone derivatives with potential psychotropic activity on cellulose tris(4‐methylbenzoate) chiral selector

2001

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The behavior of a series of 3-amino-2-oxazolidinone derivatives with a potential hypnotic activity on achiral (octadecylsilane) and chiral (cellulose tris(4methylbenzoate)) stationary phases was examined. The compounds differed in the composition of a substituted aromatic ring containing different substituents in different positions. It was possible to resolve all the compounds with selectivity 1.11 Յ ␣ Յ 2.74. The enantiodifferentiating power of substituents was correlated to their electron donating ability and position in the aromatic ring. Chirality 13: 148-152, 2001.

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Correlation of nmr Chemical Shifts with Hammett σ Values and Analogous Parameters

Cited by 32 publications

References 149 publications

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

New aryloxybenzylidene ruthenium chelates – synthesis, reactivity and catalytic performance in ROMP

Enantioselectivity of 3‐amino‐2‐oxazolidinone derivatives with potential psychotropic activity on cellulose tris(4‐methylbenzoate) chiral selector

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