A Quantitative Relationship between Dissociation Constants and Conformational Equilibria. Cyclohexanecarboxylic Acids<sup>1</sup>

Stolow, Robert D.

doi:10.1021/ja01530a064

Cited by 55 publications

(13 citation statements)

References 3 publications

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“…Cyclohexane (l), methylcyclohexane (2) and tertbutylcyclohexane (9) were obtained commercially. cisand trans-1,3-Dimethylcyclohexanes (3,4) were prepared by addition of CH3MgI to 3-methylcyclohexanone, and dehydration of the resulting 1,3dimethylcyclohexanols by KHS04 to give a mixture of…”

Section: Compoundsmentioning

confidence: 99%

Long range ¹³C shift effects (δ and ϵ) in methylcyclohexanes

Vierhapper

Willer

1977

Org. Magn. Reson.

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C n.m.r. spectra of a number of methyl substituted cyclohexanes, some of them conformationally homogeneous, have been recorded in CDCIJ and used to determine shift effects engendered by the introduction of methyl groups on carbon atoms remote from the site of substitution. Sizeable changes in shifts are found, including a substantial effect of an equatorial methyl group on an axial methyl group S to it (+0.6, ppm, ' S . , ' ) .The effects reported are of consequence in investigations of confonmtional problems by 13C n.m.r. techniques. 13Substitution parameters for 13C chemical shifts in methylcyclohexanes have been developed in the classical work of Grant and co-workers.' Grant gives parameters for the effects of equatorial and axial methyl groups, to be added to the shift of cyclohexane, for carbon atoms a, 6, y and 6 to the methyl substituent. These were calculated by a regressional analysis from the chemical shifts of a large number of methyl substituted cyclohexanes, the spectra of which were recorded as neat liquids. The ye shift, and the shifts caused by methyl substituents at more distant sites ( 3 6 ) were reported to be quite small, and a shift difference of 4.30 f 0.40 ppm between otherwise undisturbed equatorial (23.12 ppm from TMS) and axial CH3 was established.Since the work of Dalling and Grant' was reported, more advanced and sensitive n.m.r. instruments have been developed. It is now possible to measure 13C shifts with a reproducibility of better than f O . 1 pprn in solutions no more concentrated than 10%. We report here (Table 1) some revised shifts for methylcyclohexanes 1-11, recorded as 10% solutions in CDC13. The results show that t h y e are palpable 6 and E methyl substituent effects. At the current level of accuracy of 13C n.m.r. measurements, these contributions can no longer be disregarded in attempts to make predictions of shifts in new compounds. More important, in attempts to calculate free energy differences (AG = -RTlnK,,) by means of the equation3where v is the shift value of a carbon atom (ring carbon or methyl substituent) in the mobile form and ve and v, are the shifts of that carbon atom in conformationally homogeneous models, it is essential to correct for the effects brought about by even remote substituents which may act as biasing groups in the * Author to whom correspondence should be addressed.latter. (v is used through this paper to denote chemical shifts, to allow unambiguous use of S for shift effects through four bonds.)We shall illustrate these points by first calculating in detail the effect of one methyl substituent on another three carbons away (6 effects) and then tabulating similarly calculated 6 and E effects of methyl substituents on ring carbons as well as on other methyl groups. Chemical shift of an undisturbed equatorial CH3The difference in chemical shift of the methyl groups in 3 and 7 is due to the a ,, effect of the additional CH3 group in 7 (-0.22ppm). CH3 in 2 resonates at higher field than the methyl groups in 3 because 2 is conformationally inhomog...

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Section: Compoundsmentioning

confidence: 99%

Long range ¹³C shift effects (δ and ϵ) in methylcyclohexanes

Vierhapper

Willer

1977

Org. Magn. Reson.

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“…To find out the cause of this tunability, most of the previous papers aimed at steric effect and the interaction between the ions and the solvents . Besides, several reports focused on the structural properties and reactivity of the catalysts with ionic‐pair substituents .…”

Section: Introductionmentioning

confidence: 99%

“…[20,21] When pyridinium or imidazolium-substituted acetyl acetone metal compounds were used in the C-H activation reactions, our group found that the catalysts with ionic-pair substituents have higher activity than the corresponding unsubstituted counterpart. [13][14][15] To find out the cause of this tunability, most of the previous papers aimed at steric effect [22][23][24][25][26] and the interaction between the ions and the solvents. [25][26][27] Besides, several reports focused on the structural properties and reactivity of the catalysts with ionic-pair substituents.…”

Section: Introductionmentioning

confidence: 99%

The relationships of catalytic activity of metal Schiff base catalysts and the Hammett constants of their anion–cationic substituents on ligand

Chen

Liu

Yao

et al. 2015

J of Physical Organic Chem

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“…Due to the combination of different cations and anions of the catalysts with ionic‐pair substituents, their catalytic activities can be tuned in an appropriate extent . To check out the reasons for this tuneability, most of the previous papers aimed at steric and solvation effect . Besides, the electronic effect is also an important factor .…”

Section: Introductionmentioning

confidence: 99%

Electronic effect of ionic‐pair substituents

Chen

Liu

et al. 2013

J of Physical Organic Chem

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For conventional organic substituents, an almost linear relationship can be established between the para Hammett constants in aqueous solutions and chemical shifts or natural population analysis charges (NPA charges). Based on these correlations, the Hammett constants of six synthesized ionic-pair substituents were estimated via the chemical shifts, which were well in agreement with the results calculated by NPA charges. The para Hammett constants of 89 different ionic-pair substituents (77 anion-cationic and 12 cation-anionic) were therefore calculated in the gas phase based on the density functional theory method. The results show that both the anion-cationic and cation-anionic substituents are electron-withdrawing groups and the different cation-anion combinations could tune the Hammett constants of the ionic-pair substituents in a range from 0.03 to 0.77.

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A Quantitative Relationship between Dissociation Constants and Conformational Equilibria. Cyclohexanecarboxylic Acids¹

Cited by 55 publications

References 3 publications

Long range ¹³C shift effects (δ and ϵ) in methylcyclohexanes

Long range ¹³C shift effects (δ and ϵ) in methylcyclohexanes

The relationships of catalytic activity of metal Schiff base catalysts and the Hammett constants of their anion–cationic substituents on ligand

Electronic effect of ionic‐pair substituents

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A Quantitative Relationship between Dissociation Constants and Conformational Equilibria. Cyclohexanecarboxylic Acids1

Cited by 55 publications

References 3 publications

Long range 13C shift effects (δ and ϵ) in methylcyclohexanes

Long range 13C shift effects (δ and ϵ) in methylcyclohexanes

The relationships of catalytic activity of metal Schiff base catalysts and the Hammett constants of their anion–cationic substituents on ligand

Electronic effect of ionic‐pair substituents

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Product

Resources

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A Quantitative Relationship between Dissociation Constants and Conformational Equilibria. Cyclohexanecarboxylic Acids¹

Long range ¹³C shift effects (δ and ϵ) in methylcyclohexanes

Long range ¹³C shift effects (δ and ϵ) in methylcyclohexanes