Substituent effects.  III.  Dissociation constants of .beta.-arylpropionic acids, .beta.-arylisovaleric acids, N-arylglycines, aryloxyacetic acids, N-aryl-.beta.-alanines, and some related systems

Hoefnagel, A. J.; Monshouwer, J. C.; Snorn, E. C. G.; Wepster, B. M.

doi:10.1021/ja00797a040

Cited by 28 publications

(10 citation statements)

References 4 publications

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“…Jencks observed that the equilibrium transfer of acyl groups to substituted thiols or thiol anions is less sensitive to polar substituents 44. However, he did not account this to a relative poor transmission of electron‐withdrawing effect of the acyl group through sulfur compared to oxygen or nitrogen, since the “fall‐off” factors for transmission of substituent effects through X in the ionization of ArXCH 2 COOH in 50% ethanol are 0.51, 0.52, 0.38, and 0.33–0.39 for S, O, NH, and CH 2 respectively 59, 60. He proposed that the significant contribution of the resonance form 3c of thiol esters accounted for the small sensitivity to substituents on sulfur.…”

Section: Resultsmentioning

confidence: 99%

Enhanced reactivity in the ammonolysis of phenyl thiolacetates in aqueous medium

Rajarathnam

Babu

Nadar

2001

Int J of Chemical Kinetics

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The ammonolysis of several substituted phenyl thiolacetates is kinetically studied in aqueous medium, 18 • C, ionic strength 0.1 M (KCl). By following the leaving groups spectrophotometrically (λ max = 260-410 nm), under excess free ammonia, pseudo-first-order rate coefficients (k obs ) are obtained. The plots of (k obs − k H ) against free ammonia concentration are linear at constant pH. The macroscopic nucleophilic substitution rate coefficients (k N ) are obtained as the slopes of these plots and found to be pH-independent for all the thiolesters. The Brönsted-type plot (log k N against pK a of leaving groups) and the Hammett plot (log k N against σ values of substituents) obtained for the title reactions of thiolesters are linear with slope values of β lg = −0.34 and ρ = 0.74 respectively. From the magnitude of these values, experimental data, the kinetic law, and the analysis of products, it is deduced that the ammonolysis of thiolesters proceeds through a simple bimolecular nucleophilic substitution pathway with a zwitterionic tetrahedral addition intermediate (T ± ), whereby its formation is rate-determining (k 1 step). Comparison of this reaction of thiolesters with a similar reaction of analogue oxyesters shows a mechanistic difference. Further, for thiolesters there is a rate enhancement with larger k N values. The change in mechanism and enhanced reactivity observed by substitution of the oxygen atom by sulphur atom on the phenyl moiety are discussed in detail.

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Section: Resultsmentioning

confidence: 99%

Enhanced reactivity in the ammonolysis of phenyl thiolacetates in aqueous medium

Rajarathnam

Babu

Nadar

2001

Int J of Chemical Kinetics

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“…There is some information about the effect of p-NH 2 as a substituent in phenylacetic or phenylpropionic acid. From pK a values in aqueous ethanolic solutions the apparent sigma value of p-NH 2 is in the range of about 0.20 to 0.25 124,125 . (Corrections for zwitter-ion content have been applied by the authors concerned.)…”

Section: Electronic Effects Of the Amino Group And Related Groups mentioning

confidence: 99%

“…For the sake of uniformity 0 values for CR substituents have also been based on such systems. Wepster and colleagues 124,125 , however, have criticized the use of systems in which the substituent is 'insulated' by methylene groups from the reaction centre for its tendency to lead to slightly exalted values of 0 for CR substituents, i.e. the supposed insulation is not 100% effective.…”

Section: Acids Of the Type Ph−g−coohmentioning

confidence: 99%

Electronic Effects of Nitro, Nitroso, Amino and Related Groups

Shorter¹

2009

Patai's Chemistry of Functional Groups

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“…-<NMNPA is a colorless oil and was collected at vapor temperature and pressure listed (mm Hg). tHoefnagel et aL.,1973. 'Bryson et at., 1963 …”

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confidence: 99%

Substitutes for N-Phenylglycine in Adhesive Bonding to Dentin

1989

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Using bond strength measurements, we investigated a number of related compounds in order to elucidate the role of the surface-active ingredient, N-phenylglycine (NPG), in experimental two-step and three-step bonding protocols resulting in adhesive bonding to dentin. All active compounds identified for the two-step or the three-step protocol were N-aryl-alpha-amino acids, and the results delineate some of the key features of the NPG molecule for bonding. For the three-step protocol, there was a requirement for a secondary or tertiary aromatic amino group, a carboxylic acid group, and a single (secondary or tertiary) methylene unit between those two functional groups of the amino acid. For the two-step protocol, additional substitutions at the para position of the phenyl ring on the amine improved the bond strength. In both protocols, para-methyl- and para-chloro-substituted NPG analogues ranked higher than NPG. A "catalytic" effect of the aromatic tertiary amino group on the polymerization of the adhering resin in both procedures could not be ruled out.

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Substituent effects. III. Dissociation constants of .beta.-arylpropionic acids, .beta.-arylisovaleric acids, N-arylglycines, aryloxyacetic acids, N-aryl-.beta.-alanines, and some related systems

Cited by 28 publications

References 4 publications

Enhanced reactivity in the ammonolysis of phenyl thiolacetates in aqueous medium

Enhanced reactivity in the ammonolysis of phenyl thiolacetates in aqueous medium

Electronic Effects of Nitro, Nitroso, Amino and Related Groups

Substitutes for N-Phenylglycine in Adhesive Bonding to Dentin

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