The transmission of polar effects: the reversed dipolar substituent effect

Bowden, Keith; Parkin, D. C.

doi:10.1039/c1968000075b

Cited by 6 publications

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“…This small reversal or greatly diminished substituent effect has been previously observed in isolated cases for cis-ortho-substituted cinnamic acids (25,12). This is considered to arise from a reversed dipolar substituent field effect (13,26). Catalin models show that in favorable conformations of the cis-cinnamic acids the ortho-substituent can be very close to the reaction site (1).…”

Section: Resultsmentioning

confidence: 99%

The transmission of polar effects. Part VIII. Esterification with diazodiphenylmethane and the ionization of ortho-substituted trans-cinnamic, phenoxyacetic, 3-phenylpropionic, cis- and trans-α-phenylcinnamic acids

Bowden¹,

Parkin²

1968

Can. J. Chem.

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The rate coefficients for the esterification with diazodiphenylmethane in ethanol at 30" and the pK, values at 25" of a number of ortho-substituted trans-cinnamic, phenoxyacetic, 3-phenylpropionic, ortho-, meta-, and para-substituted cis-and trans-cr-phenylcinnamic acids have been determined. The effects of substitution have been assessed by a Hanimett-type correlation. A comparison of the transmission of the polar effects of ortho and metalpara substituents indicates the prime importance of the field effect, augmented where possible by ax-inductive effect. A reversed dipolar substituent field effect has been detected for the cis-ortho-substituted cinnamic acids.Canadian Journal of Chemistry, 46. 3909 (1968) Introduction In a search for model systems to distinguish between the inductive and field effects (1, 2), a previous analysis (3) suggested that for certain reaction and substituents, the polar effect of ortho-substituents in benzoic acids is transmitted approximately twice as efficiently as that of metalpara-substituents. A very simple test presents itself. If the field effect is the main means of transmission, the ratio will decrease and approach unity as the substituted phenyl group becomes more distant from the reaction site. This is due to the field effect varying with cos 0/r2 for a point dipole (4), where r is the distance from the dipole and the reaction site and 0 is the angle between r and the dipole. However, if an inductive effect is mainly responsible, the ratio will remain the same. This is because the inductive effect decreases by a factor E for each intervening link (2,5).In this study, the reactivities of a series of ortho-substituted trans-cinnamic, phenoxyacetic, 3-phenylpropionic, cis-and traiw-ci-phenylcinnamic acids in their ionization and their reaction with diazodiphenylmethane in ethanol have been studied, together with the metalpara-substituted a-phenylcinnamic acids. The ortho-substituted -systems have been correlated by a Hammett-type equation and compared with the

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Section: Resultsmentioning

confidence: 99%

The transmission of polar effects. Part VIII. Esterification with diazodiphenylmethane and the ionization of ortho-substituted trans-cinnamic, phenoxyacetic, 3-phenylpropionic, cis- and trans-α-phenylcinnamic acids

Bowden¹,

Parkin²

1968

Can. J. Chem.

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“…The question of whether substituent effects other than mesomeric effects are transmitted through bonds (inductive effects) or through space (electric field effects) is still under investigation, largely by measurements of acid dissociation constants (1)(2)(3)(4). However, Buckingham has derived an equation (9, AS = AE, + BE^, which allows one to predict the change in proton chemical shifts, AS, due to intra-and intermolecular electric fields.…”

Section: Introductionmentioning

confidence: 99%

Evidence for the existence of an electric field effect from the vinyl proton magnetic resonance spectra of 4-substituted styrenes

Hamer¹,

Reynolds²

1968

Can. J. Chem.

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Vinyl proton chemical shifts of styrene and six 4-substituted styrenes have been determined at infinite dilution in cyclohexane. It is shown that changes in the chemical shift difference of the β protons, Δ(δC − δB) can be accounted for by electric field effects. Reasonable values of the constant in the Buckingham equation of(−3.11 ± 0.50) × 10−12 and (−4.77 ± 0.83) × 10−12 are obtained from two different types of field effect calculations. Residual chemical shift changes for β protons after correction for electric field effects can be explained in terms of mesomeric and possibly inductive mechanisms. α-Proton chemical shift values cannot be satisfactorily rationalized. Small concentration effects are noted, usually resulting in high field shifts with increasing concentration. Previous results are reexamined in order to resolve a conflict in the literature.

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“…A similar effect has been noted for 8-substituted 1-naphthoic acids. 7 The geometrical disposition of the bromo group in the pseudo-gemand pseudo-ortho-isomer is such that the negative end of the dipole can interact significantly with both incipient negative and incipient positive charges in the transition state for esterification. In equilibria ionisation the final state is anionic alone.…”

Section: Resultsmentioning

confidence: 99%

Transmission of polar effects. Part 15. Ionisation and esterification with diazodiphenylmethane of [2.2]paracyclophane-4-carboxylic acid and its pseudo-bromo-substituted derivatives, and the alkaline hydrolysis of their methyl esters

Acevedo¹,

Bowden²

1986

J. Chem. Soc., Perkin Trans. 2

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lchester C04 3S0, EssexThe pK, values of [2.2] paracyclophane-4-carboxylic acid and its four pseudo-bromo-su bstituted derivatives have been determined in 80% (w/w) 2-methoxyethanol-water at 25 "C. The rate coefficients for the esterification of these acids with diazodiphenylmethane have been measured in 2methoxyethanol at 30 "C. The rate coefficients for the alkaline hydrolysis of the corresponding methyl esters have been determined in 70% (v/v) dimethyl sulphoxide-water at both 56.3 and 76.3 "C. In the ionisation and esterification reactions both normal and reversed su bstituent polar effects were detected. Kirkwood-Westheimer calculations were carried out for the ionisation reaction and account for ApK, values both qualitatively and (for the pseudo-ortho-, -meta-, and -para-isomers) quantitatively. In the alkaline hydrolysis of the esters, significant steric retardation was observed for the pseudo-gern-isomer.From previous work on inductive and electrostatic-field effect model^,^-^ a field-effect model appears to give the more satisfactory description of the substituent polar effect. A reversal of the normal polar effect has been detected in some of these system^^-^ and such behaviour has been accounted for in terms of the angular dependence of the polar effect. Thus either the normal or the reverse of the normal substituent polar effect would be expected on the basis of the geometrical disposition of the substituent with regard to the reaction centre.We describe here the ionisation of [2.2]paracyclophane-4carboxylic acid and its four pseudo-bromo derivatives (l), their esterification with diazodiphenylmethane (DDM), and the alkaline hydrolysis of the corresponding methyl esters.' The results are related to Kirkwood-Westheimer calculations of the electrostatic field effect.

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The transmission of polar effects: the reversed dipolar substituent effect

Cited by 6 publications

References 0 publications

The transmission of polar effects. Part VIII. Esterification with diazodiphenylmethane and the ionization of ortho-substituted trans-cinnamic, phenoxyacetic, 3-phenylpropionic, cis- and trans-α-phenylcinnamic acids

The transmission of polar effects. Part VIII. Esterification with diazodiphenylmethane and the ionization of ortho-substituted trans-cinnamic, phenoxyacetic, 3-phenylpropionic, cis- and trans-α-phenylcinnamic acids

Evidence for the existence of an electric field effect from the vinyl proton magnetic resonance spectra of 4-substituted styrenes

Transmission of polar effects. Part 15. Ionisation and esterification with diazodiphenylmethane of [2.2]paracyclophane-4-carboxylic acid and its pseudo-bromo-substituted derivatives, and the alkaline hydrolysis of their methyl esters

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