Oxygen-17 NMR spectroscopy: torsion angle relationships in aryl carboxylic esters, acids and amides

Baumstark, Alfons L.; Balakrishnan, P.; Dotrong, M.; Mccloskey, C. J.; Oakley, Martha G.; Boykin, David W.

doi:10.1021/ja00238a013

Cited by 95 publications

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“…[ [12][13][14] Although there are numerous investigations on the δ( 17 O) values for esters in literature, the influence of the substituent effects on the δ( 17 O of the carbonyl and methoxy oxygens in esters of substituted benzoic acid, using correlation equations, has been studied only for meta-and para-substituted methyl benzoates and para-substituted methyl 2,6-dimethyl-4-X-benzoates. [14][15][16] The δ( 17 O) values of carbonyl and methoxy oxygens in meta-and para-substituted methyl benzoates gave good correlations with σ m and σ + constants, respectively.…”

Section: The Values Of δ(mentioning

confidence: 99%

“…In the hindered benzoates, 2,6-dimethyl-4-X-benzoates, the through-conjugation was found to be essentially reduced due to the increased torsion angle between the carbonyl group and the ring plane. [13,14] It was found that in methyl benzoates reaction series an introduction of electron-attracting substituents causes deshielding and electron-donating substituents shielding of the carbonyl and methoxy O atoms. [14][15][16] It has been shown [26][27][28][29] that in substituted carbonyl derivatives, Y-C 6 H 4 CO-X, RCO-X, the shielding of the carbonyl oxygen is increased and the sensitivity of the Y substituent is diminished with an increase in the electron-donating power of the X group.…”

Section: The Values Of δ(mentioning

confidence: 99%

“…In orthosubstituted derivatives the steric influence of ortho substituents on the δ( 17 O) values has been explained by steric inhibition of resonance and van der Waals interactions. [12][13][14]17,39,[41][42][43][44] It was suggested that in systems in which the functional group is free to rotate, due to sterical consequences the functional group is rotated out of the plane of the aromatic ring increasing the double bond character of the functional group. In the rigid systems the steric influence of ortho substituents was explained by the van der Waals interactions between the ester group and the adjacent bulky substituent.…”

Section: The Values Of δ(mentioning

confidence: 99%

“…In our previous papers the influence of substituent effects, especially ortho effect, on the rates of the alkaline hydrolysis in various media (as shown in References [1][2][3][4][5][6][7] ), the carbonyl carbon 13 C NMR chemical shifts, δ CO , [8] and the carbonyl carbon infrared stretching frequencies, ν CO , [9] in substituted phenyl benzoates, (X-C 6 H 4 CO 2 C 6 H 5 , C 6 H 5 CO 2 C 6 H 4 -X) were studied. In the present paper we extend our study of the ortho substituent effect to the To the best of our knowledge, no study of the ortho, meta, and para substituent effects on the δ( 17 O) values for phenyl esters of substituted benzoic acids, X-C 6 H 4 CO 2 C 6 H 5 , could be found in the literature.…”

Section: Introductionmentioning

confidence: 99%

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Influence of ortho substituents on ¹⁷O NMR chemical shifts in phenyl esters of substituted benzoic acids

Nummert

Mäemets

Piirsalu

et al. 2010

J of Physical Organic Chem

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Abstract17O NMR spectra for 29 phenyl esters of ortho‐, para,‐ and meta‐substituted benzoic acids, X‐C6H4CO2C6H5, at natural abundance in acetonitrile were recorded. The δ(17O) values of carbonyl and the single‐bonded oxygens for para derivatives gave good correlation with the σ+ constants. The δ(17O) values for meta derivatives correlated well with the σm constants. The influence of ortho substituents on the δ(17O) values of carbonyl oxygen and the single‐bonded oxygens was analyzed using the Charton equation containing the inductive, σI, resonance, σ+R, and steric, E, substituent constants. For ortho derivatives, excellent correlations with the Charton equation were obtained when the data treatment was performed separately for derivatives containing electron‐donating +R and electron‐attracting −R substituents. The electron‐donating substituents in ortho‐, meta‐, and para‐substituted esters resulted in shielding of the 17O signal and the electron‐withdrawing groups caused deshielding. In phenyl ortho‐substituted benzoates, the substituent‐induced positive inductive (ρI > 0), resonance (ρR > 0), and steric (δorthoE > 0) effects were found. The steric interaction of ortho substituents with ester group was found to produce a deshielding effect on the carbonyl and single‐bonded oxygens. For ortho derivatives with −R substituents, the resonance term was insignificant and the steric term was ca. twice weaker as compared to that for derivatives with +R substituents. The δ(17O) values for ortho‐substituted nitrobenzenes, acetophenones, and benzoyl chlorides showed a good correlation with the Charton equation as well. In ortho‐substituted nitrobenzenes the inductive, resonance and steric effect were found to be ca. 1.7 times stronger as compared to that for phenyl ortho‐substituted benzoates. Copyright © 2010 John Wiley & Sons, Ltd.

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Section: The Values Of δ(mentioning

confidence: 99%

Section: The Values Of δ(mentioning

confidence: 99%

Section: The Values Of δ(mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Influence of ortho substituents on ¹⁷O NMR chemical shifts in phenyl esters of substituted benzoic acids

Nummert

Mäemets

Piirsalu

et al. 2010

J of Physical Organic Chem

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“…De um modo geral, vários fatores influenciam a reatividade em ataques eletrofílicos do borano ao oxigênio, sendo dependente das condições estéricas tanto da amida 110 quanto do borano 111 . Além disso, a acidez dos boranos é também muito importante na determinação dos produtos e seletividade da redução envolvendo compostos carbonílicos 112 .…”

Section: (32)unclassified

Redução de amidas por boranos

2002

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Recebido em 27/3/01; aceito em 25/7/01 REDUCTION OF AMIDES BY BORANES. Despite the fact that boranes are frequently used in amide reductions, the reaction mechanisms of the involved are note well known. This work presents the results of a bibliographic search on probable amide reduction mechanisms and an analysis of the existing literature. Steric and electronic effects were considered in light of reactivity since it could be concluded that the formation of intermediates and products depends mainly on the substitution patterns of both the boron and nitrogen atoms. Otherwise, results described in the literature for the reactions of boranes, sodium borohydride, lithium aluminum hydride, alkylboranes or haloboranes with others functional groups such as carboxylic acids, esters, ketones and alkenes were analysed with the aim to obtain something about the N-substituted amide reactions employing boranes.Keywords: amides; reactivity of boranes; reduction. INTRODUÇÃOAmidas estão envolvidas em vários processos químicos e bioló-gicos e têm sido empregadas em diversas classes de medicamentos como hipnóticos (zolpidem, zopiclone e acecarbromal), anticonvulsantes (carbamazepina, felbamato e progabida), tranqüilizan-tes (metilprilona e glutetimida), relaxantes musculares (alildietilacetamida, valnoctamida e oxanamida) e antivirais (AZT e ribavirin) 1-3 . Além disto, as amidas são empregadas também na síntese de agentes radiofarmacêuticos em medicina nuclear 4 .De um modo geral, as propriedades químicas e biológicas das amidas estão relacionadas com a ordem da ligação carbono-nitrogê-nio, a qual expressa a deslocalização eletrônica entre os heteroátomos, sendo influenciada por fatores estéricos e eletrônicos dos grupos substituintes presentes tanto no nitrogênio quanto no carbono carbonílico. Devido à deslocalização eletrônica, essa ligação (denominada também de ligação peptídica) apresenta um alto grau de rigidez, com barreiras de energia rotacional variando entre 50 e 100 kJ/mol 5,6 . A rigidez da ligação carbono-nitrogênio proporciona uma planaridade ao grupo amido em peptídeos e proteínas, a qual, somada aos efeitos de ligações de hidrogênio intramoleculares, determina formas estruturais helicoidais (Figura 1).Nos processos químicos, as reduções de amidas têm sido muito empregadas no desenvolvimento de metodologias para formação de aminas, substâncias também importantes quimicamente 8 . Os procedimentos utilizados para reduções de amidas podem ser agrupados em quatro tipos: reações eletroquímicas; reações com metais; reduções nucleofílicas e reduções eletrofílicas.As reações eletroquímicas e aquelas envolvendo metais são dependentes das condições de reação 9,10 , podendo levar à formação competitiva entre aminas, aldeídos ou álcoois [11][12][13][14][15][16][17] . As reduções nucleofílicas, empregando principalmente boro-hidreto de sódio (NaBH 4 ), hidreto de lítio e alumínio (LiAlH 4 ) e seus derivados 18-28 , proporcionam, além de aminas, a formação de outros produtos de reação. Assim, tris-(dialquilamino)-alumino-hidreto...

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Steric Effects and Steric Hindrance to Resonance intert-Butylbenzoic Acids in the Gas Phase and in Solution

et al. 1999

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Substituent effects of the tert‐butyl group in isomeric tert‐butylbenzoic acids have been investigated on the basis of enthalpies of formation, gas‐phase acidities, acidities in methanol and in dimethyl sulfoxide, and the IR spectra in tetrachloromethane. In contrast to 2‐methylbenzoic acid, 2‐tert‐butylbenzoic acid must adopt a non‐planar conformation, as is confirmed by its IR spectrum. Enhanced acidity in the gas phase has been found for all isomers and attributed to a pole‐induced dipole interaction in the anion (polarizability effect); in the ortho isomer the steric inhibition of resonance is only responsible for a minor part of the observed effect. In solution, the electrostatic interaction is attenuated, but remains strong in the case of the ortho isomer.

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Oxygen-17 NMR spectroscopy: torsion angle relationships in aryl carboxylic esters, acids and amides

Cited by 95 publications

References 0 publications

Influence of ortho substituents on ¹⁷O NMR chemical shifts in phenyl esters of substituted benzoic acids

Influence of ortho substituents on ¹⁷O NMR chemical shifts in phenyl esters of substituted benzoic acids

Redução de amidas por boranos

Steric Effects and Steric Hindrance to Resonance intert-Butylbenzoic Acids in the Gas Phase and in Solution

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Oxygen-17 NMR spectroscopy: torsion angle relationships in aryl carboxylic esters, acids and amides

Cited by 95 publications

References 0 publications

Influence of ortho substituents on 17O NMR chemical shifts in phenyl esters of substituted benzoic acids

Influence of ortho substituents on 17O NMR chemical shifts in phenyl esters of substituted benzoic acids

Redução de amidas por boranos

Steric Effects and Steric Hindrance to Resonance intert-Butylbenzoic Acids in the Gas Phase and in Solution

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Influence of ortho substituents on ¹⁷O NMR chemical shifts in phenyl esters of substituted benzoic acids

Influence of ortho substituents on ¹⁷O NMR chemical shifts in phenyl esters of substituted benzoic acids