Neighboring Group Effect Research Articles

Quaternization of poly(4-vinyl pyridine). Kinetic and viscometric measurements

Quaternization reactions of poly(4-vinyl pyridine) with n-alkyl bromides in propylene carbonate as solvent have been carried out, with and without added low molecular weight pyridinium salts, to give a comparison under these conditions of reaction kinetics, viscosities of reacting mixtures and cloud-point temperatures, where relevant. There is no primary salt effect on the kinetics; the kinetic behaviour is virtually unaltered by salt, i.e., the neighbouring-group retardation is preserved, except that in some cases the salt induces eventual clouding of the reacting system and extreme retardation of the reaction; the viscosity of a reacting system expressed as a reduced viscosity (viscosity number) passes through a maximum in the absence of salt, but this is suppressed when salt is present. The observations are explained mainly on the basis of a neighbouring-group effect involving steric hindrance, and a global effect where polymer molecules initially expand during reaction, and then contract as the solvent quality diminishes. Addition of salt prevents coil expansion and induces salting out; there could also be binding of the salt to the polymer.

Structural studies of extracellular glucans of Streptococcus mutans by proton magnetic resonance

Proton magnetic resonance spectra at 100 MHz were obtained for water-soluble and water-insoluble glucans from 11 strains of Streptococcus mutans. The percentages of α- D-(1→6) and non-α- D-(1→6)-, namely, α- D-(1→3)-, linkages were calculated from the anomeric-proton resonances in the 4.7-4.8 and 5.0-5.1 p.p.m. range, respectively. The average content of α- D(1→6) linkages in the polymer fractions precipitating from solution during synthesis of the glucans was generally much lower than that of fractions remaining in solution. The frequent appearance of the α- D-(1→3) resonances as doublets in the spectra suggested neighboring-group effects among the possible α- D-(1→3) and α- D-(1→6) linkage-configurations. These effects were confirmed from 100-MHz spectra of products of a dextranase-degraded, water-insoluble glucan, and a 270-MHz spectrum of an undegraded glucan. It was thus possible to assign the doublet resonances to α- D-(1→3), homogeneous, heterogeneous, and branch configurations, although complete differentiation among proportions of each configuration in the glucan chains could not be achieved.

Neighboring general acid participation in thiolester aminolysis in an aprotic solvent

The kinetics of n-butylaminolysis of acyl-substituted phenyl tiolbenzoates in acetonitrile at 25°C was studied. From the second order rate constants a Hammett rho value of 1.45 was obtained. The results indicate a proinounced neighboring group effect in the reaction of phenyl thiolsalicylate, providing the first kinetic evidence for intramolecular general acid participation by a hydroxy function in an aprotic solvent.

Neighbouring group effects in the addition of hypobromous acid to unsaturated steroids

The reaction of the stereoisomeric 3-hydroxy(or acetoxy)-5α-cholest-1-enes and 1-hydroxy(or acetoxy)-5α-cholest-2-enes with N-bromoacetamide was investigated. With one exception [formation of the bromo-diol (15a)], the reactions take place by initial formation of an α-oriented bromonium ion; the 2α,3α-ions are preferentially attacked at C(3)(β with respect to the neighbouring group), leading to trans-diequatorial products, whereas the 1α,2α-bromonium ions are invariably attacked at C(2)(α with respect to the neighbouring group), leading to diaxial products. In two instances, internal nucleophilic displacement by appropriately oriented hydroxy-groups leads to bromo-epoxides [compounds (3) and (16)].

Some Recent Advances in the Study of the Reactivity of Systems Containing Polymers

AbstractRecent studies of reaction rates in polymer systems are reviewed. These involve ionic reactions in polyelectrolyte solutions, kinetic effects due to the nature of the “effective solvent medium” in the polymer domain, neighboring group effects in polysaccharide oxidation, intramolecular polymer reactions involving non‐neighboring groups, the quenching of the fluorescence of groups attached to a polymer by species carried by another polymer chain and the photoisomerization of azobenzene residues in the backbone of polymer chains.

Leaving group, steric and substituent effects in highly congested systems: The acid-catalysed dehydration of aryldi-tert-butylcarbinols and the solvolysis of their p-nitrobenzoates

Ortho-tolyldi-t-butylcarbinols exist in two well-defined, stable forms: and-periplanar. 3 and syn-periplanar. 5. The rate constant for the acid-catalysed dehydration of the ap isomer in anhydrous acetic acid at 25°C is about 10 4 times greater than that of the sp isomer. Generally speaking, the high reactivity of the ap alcohols is due to ground state steric strain, but secondary steric effects upon resonance stabilisation of the intermediate carbonium ion and entropy effects lower the rate ratio in the case of the 4-methoxy and prehnityl derivatives. respectively. The activity of phenyldi-t-butylcarbinols, 4 lies halfway between that of 3 and 5. When p-nitrobenzoyl chloride is added to the 3 and 5 alkoxides, only the ap alcohol gives a p-nitrobenzoate, 2. This PNB solvolyses at 25° about 10 3 times faster than phenyldi-t-butylcarbinyl PNB. 1. Comparison of the rate ratios for alcohol dehydration ( 3/4) and PNB solvolysis ( 2/1) shows that the leaving group has only a small effect upon the ortho-tolyl/phenyl rate ratio. Reaction constants, ϱ for alcohol dehydration are very similar for the three series (−4.19, −3.90 and −4.12 for 3, 4 and 5, respectively) showing thus little variation of substituent-sensitivity with reactivity. In contrast, that of the more reactive PNB, 2 is −1.93, amongst the lowest ever found for S N1 solvolysis, white that of 1is very different, −2.96. Since neighbouring group effects are absent in these systems, these latter variations can only be attributed to differences in the extent of charge separation in the solvolysis transition state. both being earlier than that of t-cumyl PNB (ϱ = −4.60).

Neighbouring group effects in the acid-catalysed opening of steroidal epoxides

The hydrobromic-acid-induced opening of the epoxide ring in the stereoisomeric 1-hydroxy(or -acetoxy)-2,3-epoxy- and 3-hydroxy(or -acetoxy)-1,2-epoxy-5α-cholestanes was investigated. The results are evaluated with regard to the tendency to ‘diaxial opening’ of the epoxide ring and the tendency of the nucleophile to attack at the carbon atom β with respect to the neighbouring group. The 2α,3α-epoxides give mixtures of diaxial and di-equatorial products, whereas 2β,3β-epoxides give only diaxial products. All products obtained from 1,2-epoxides are diaxial. In several instances, the epoxide ring is displaced by an appropriately oriented acetoxy-group.

Gas phase 1,3-deoxystannylation reactions of γ-substituted organotin alcohols utilizing chemical ionization mass spectrometry

The gas phase 1,3-deoxystannylation reactions of γ-substituted organotin alcohols have been studied by methane and isobutane chemical ionization mass spectrometry. It was found that γ-hydroxybutyltributyltin and γ-hydroxybutyldibutyltin chloride undergo the 1,3-deoxystannylation reaction to a greater extent than the corresponding 1,4-deoxystannylation using the δ-substituted analogues of the above named compounds. This result substantiates the unusual reactivity of γ-substituted organotin alcohols under gas phase protonolysis conditions. The electronic factors affecting the stabilization of the transition state were ascertained with γ-phenyl-γ-hydroxypropyltrimethyltin derivatives, in which the γ-phenyl group was substituted with groups such as H, p-OMe, p-Me, p-Cl, p-F, m-OMe, m-Me, m-Cl and m-CF 3. We observed a reasonably linear Hammett relationship when plotting the log [P − 17] x +/[P − 17] H + vs. σ + with rho (ρ) equal to −1.0. Thus electron-donating groups stabilize the [P − 17] + ion and carbon—tin sigma (σ) electrons can either, by a neighbouring group effect, attack the nucleofugic center, or the carbonium ion can attack the carbon—tin σ electrons to form the trimethyltin cation and a cyclopropane derivative. Consequently, we propose that a two-step mechanism for the 1,3-deoxystannylation reaction is operating in the gas-phase with this type of compound. The factors contributing to this gas phase reaction will be discussed.

Couplages a longue distance dans des structures rigides. Stereochlmie d'alkyudene cyclopentenones

A study of the neighbouring group effects on the 1H and 13C chemical shifts and the results of NOE experiments have allowed the identification of the stereoisomers of alkylidene cylopentenones. Various long range coupling constants have been measured and their signs determined by selective decoupling. The mechanisms and angular dependences of these couplings have been discussed. The Π contributions are predominant and the absolute value of 4J transoid associated with a dihedral angle of 30° is higher than the corresponding value of 4J cisoid.

Pyrolysis of aryl azides. IV. Neighbouring group effects by ortho carbonyl groups

The question of the mechanism by which ortho carbonyl groups enhance the rate of pyrolysis of aryl azides is examined. Rate measurements on sterically hindered 1-(2-azidophenyl)ethan-1-ones are consistent with the pericyclic mechanism proposed by Dyall and Kemp1 but not with the intramolecular 1,3-dipolar addition route put forward by Hall, Behr and Reed.2 A definitive test of mechanism is also provided by 1- azidoanthraquinone and 1-(2-azidophenyl)-2,2-dimethylpropan-1-for both of which the formation of a 1,3-dipolar adduct is precluded on steric grounds but the pericyclic process is not. At 393.2 K, these two azides pyrolyse 7385 and 61.7 times faster than phenyl azide, respectively.

Additions and Corrections - Neighboring Group Effect in Heme-Carbon Monoxide Bonding

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAdditions and Corrections - Neighboring Group Effect in Heme-Carbon Monoxide Bonding C. Chang and T. TraylorCite this: J. Am. Chem. Soc. 1976, 98, 21, 6765Publication Date (Print):October 1, 1976Publication History Published online9 February 2004Published inissue 1 October 1976https://doi.org/10.1021/ja00437a606RIGHTS & PERMISSIONSArticle Views14Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (164 KB) Get e-Alerts Get e-Alerts

Problems of Polymer Modification and the Reactivity of Functional Groups of Macromolecules

Abstract General approach to the study of kinetics and mechanism of macromolecular reactions in comparison with the reactions with low molecular substances is developed. The neighbouring group effect in the transformation of functional groups of macromolecules is considered on the experimental basis of chlorination reaction with parafines, cycloparaflnes and polyethylene, acid and base hydrolysis of polymethyl methacrylate and polydiphenylmethyl methacrylate of different microstructure and of quaternization of polyvinyl pyridine. The effect of microtacticity and of conformational peculiarity on kinetical behaviour of various polymeric samples in polymeranalogous reaction is considered. A new computer technique to calculate the individual rate constants for macromolecular reactions is described and the theoretical approach to estimate the units distribution sequences and the composition heterogeneity of the products is developed. The reactions of the macromolecule-macromolecule type are reviewed in the case when the intermacromolecular interaction leads to form polycomplexes and new polymeric products of ladder-type structure and the possibility to simulate this interaction with the aid of display attachment to the computer is demonstrated.

Zero bridge cleavage and a neighboring hydroxyl group effect in the oxymercuration of bicyclo[3.1.0]hexanes

Zero bridge cleavage and a neighboring hydroxyl group effect in the oxymercuration of bicyclo[3.1.0]hexanes

天然物化学における隣接基効果

Some substiuents may influence a reaction by stabilizing a transition state or intermediate by becoming bonded or partially bonded with or without reagent to the reaction center. This behavior is called neighboring group effects. If the intermediate is stabilized in this way, the reaction rates are increased Therefore, the effects play an important role in producing regio-and stereoselectivity of a reaction. This review is described on the neighboring group effects in the field of natural product chemistry, especially steroids, terpeues, alkaloids and acetogenins.

Neighbouring group effects in epoxide ring opening; cis-epoxy-alcohols

The relative importance of polar and steric influences on the course of the acid-catalysed opening of several epoxycholestanes bearing a vicinal cis-hydroxy- or -acetoxy-group has been investigated.

Reaction of o-carboxyphenyl sulfoxides with acetic anhydride : Kinetic studies on the neighboring group effect of ortho-carboxyl group in the oxygen exchange and Pummerer reactions

Kinetic studies on the concurrent oxygen exchange and racemization reactions and Pummerer reaction of o-carboxyphenyl sulfoxides with acetic anhydride were carried out. In the reaction of o-carboxyphenyl phenyl sulfoxide, ortho-carboxyl group was found to enhance the rates of both oxygen exchange and racemization about 180 times, and the rate of racemization was nearly twice that of oxygen exchange. In the reaction of alkyl o-carboxyphenyl sulfoxides, an intramolecular Pummerer reaction took place to give 3,1-benzoxathian-4-one derivatives, and the Pummerer reaction was accelerated about 140 times that of the usual unassisted Pummerer reaction of aryl methyl sulfoxide. A very small deuterium kinetic isotope effect (k H/k D = 1.07 with trideuterated-methyl o-carboxyphenyl sulfoxide) and the rate-enhancing effect of α-alkyl group were also noticed. The markedly large rate-enhancement of both oxygen exchange and the Pummerer reactions is undoubtedly caused by the neighboring group participation of carboxyl group in the rate-determining intramolecular acylation of sulfinyl O atom.

Reaktionen von Jod-tris-(trifluoracetat) mit aliphatischen Jodverbindungen

The present paper deals with the behaviour of various alkyliodides towards J(OCOCF3)3 bearing a suitable functional group which can serve as an internal nucleophile. All the products found1–8 can be explained without any doubt by a typical neighbouring group effect with the bis-trifluoroacetoxyiodine anion, J(OCOCF3)2−, as an easily displaced leaving group.

Reaktionen mit phosphororganischen Verbindungen. XLI[1]. Neuartige synthetische Aspekte des Systems Triphenylphosphin‐Azodicarbonsäureester‐Hydroxyverbindung

New preparative methods using triphenylphosphine‐diethyl‐azodicarboxylate‐hydroxycompound.The present paper deals with new preparative methods by which the system of triphenylphosphine‐diethylazodicarboxylate‐hydroxycompound is treated with many nucleophiles. On one side, the transformation of 5α‐cholestane‐3β‐ol to the 3α‐substituted derivatives 2a‐2e (Scheme 1) by hitherto unregarded nucleophiles like azide, cyanide, thiocyanate, trifluoroacetate and thiophenoxide is shown. Further examples demonstrate the great applicability of the reaction in the case of sensitive substrates. Cholesterol (5) is transformed to the 3α‐derivative 6a without any neighbouring group participation by the Δ5‐double bond. The analogous transformation of the hydroxysteroides 7 and 9 to the corresponding 3α‐substituted compounds 8a and 10a represent further examples to be noted. Noteworthy is also the formation of the epi‐vitamine D3‐p‐nitrobenzoate from the vitamin‐D3 itself. On the other side the sources for nucleophils require special consideration. Scheme 1 demonstarates that the anions of phosphonium salts can be used as the nucleophils as is shown by the preparation of the derivatives 2a, 2c, 2f, 2h and 2i from 5α‐cholestane‐3β‐ol (1). From scheme 2 one can see the very useful preparative fact (1→2f, 2g, 2h, 21 and 2m) that alkylhalides, alkylsulfates and alkylsulfonates can be used for supplying of the corresponding nucleophile. The possibility of a direct tosylation of a chiral hydroxycompound with inversion of configuration‐as it is shown by transformation of (S)‐2‐butanol to the tosylate, obtained also from (R)‐2‐butanol and tosylchloride is a further is a further remarkable point. The absence of neighbouring group effects allows also to prepare cis‐1, 2‐ disubstituted cyclohexane compounds type C6H10 (X) (Y) (X = N3, Cl, Y = N3, J) from the corresponding trans‐1,2‐disubstituted cyclohexanoles C6H10 (X) (OH) (X = N3, Cl). The synthesis of the compounds 14a‐15d can be regarded as representative of this new useful methodic principle.

Reaction kinetics of polymer substituents : neighbouring-group effects for ideal molecules with unique ends and related model schemes

A formal kinetic analysis has been carried out for the irreversible occupation of a linear array of m sites by taking n adjacent sites at each step. Included in the model are unique probabilities for the occupation of ends of the array, and parameters permitting overall cooperative or anti-cooperative behaviour. Isolation statistics and related aspects are also described. The models treated here and previously arise from consideration of polymer transformation reactions, and discussions of reactions of synthetic polymers are augmented here by reference to polysaccharides. Scission reactions are briefly discussed.

ChemInform Abstract: DISIC ACIDS, A STUDY OF A NEW SERIES OF STRONG ORGANIC ACIDS AND THEIR CONDENSATION PRODUCTS WITH ALDEHYDES

AbstractDie Dissoziationskonstanten der Titelsäuren wie z.B. 4‐(p‐X‐Phenyl)‐3,5‐dihydroxyisoxazol mit X: Nitro, Cl und Methoxy werden bestimmt.