Oxyanion Research Articles

Model calculations of isotope effects. VII. Deprotonation of 2-nitropropane by oxy anion bases

Model calculations of primary and secondary deuterium isotope effects for the hydroxide-induced deprotonation of 2-nitropropane are reported. Various transition-state models have been examined in an effort to reproduce experimental results. A purely pyramidal transition state in which proton transfer has run far ahead of carbon rehybridization and charge delocalization is a successful model as far as isotope effects are concerned, but may fail on other counts. Three incipient trigonal models for the transition state have been tested, and, although none can be firmly eliminated by the resultant isotope effects, those involving the proton transfer's running ahead of electron delocalization and perhaps carbon rehybridization are favoured.

Esr studies on the reactive character of the radical anions, so −2, so −3 and so −4 in aqueous solution

The reactive characteristics of the oxy anion radicals of sulphur, SO − 2, SO − 3 and SO − 4 were investigated by use of the rapid-mixing flow technique coupled with electron spin resonance (ESR) which can detect the radicals having a lifetime of 5–100 msec. The SO − 2 reduced the aromatic nitro compounds to the corresponding anion radicals, but did not abstract the hydrogen from the saturated compounds nor add to the unsaturated compounds. The SO − 3 could add to the compounds having CC bond, but did not abstract the hydrogen from the saturated compounds nor reduce the aromatic nitro compounds. The SO − 4 could abstract the hydrogen from the saturated compounds and also add to the unsaturated compounds having CC bond, but did not reduce the aromatic nitro compounds. These differences of the reactivity towards the organic substrates were discussed on the basis of the difference in the distribution of the unpaired electron density of each radical anion.

Coordination of water in alkali metal oxy anion glasses

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCoordination of water in alkali metal oxy anion glassesG. Ritzhaupt and J. P. DevlinCite this: Inorg. Chem. 1977, 16, 2, 486–488Publication Date (Print):February 1, 1977Publication History Published online1 May 2002Published inissue 1 February 1977https://doi.org/10.1021/ic50168a054RIGHTS & PERMISSIONSArticle Views19Altmetric-Citations2LEARN 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 (452 KB) Get e-Alerts Get e-Alerts

Dehydration studies of 8a-Methyldecahydronaphthalen-4a-ols

The H2SO4-HOAc-Ac2O-catalysed dehydration of the epimeric 8a-methyldecahydronaphthalen-4a- ols has been shown to occur regiospecifically without skeletal or methyl migration, by loss of a proton syn to the departing anionic moiety. The results are interpreted in terms of the intermediacy of a tight ion pair where the oxy anion acts as the base in the removal of the proton. The introduction of an electron-withdrawing substituent at Cl, syn to the 8a-methyl of 8a-methyl-trans-decahydronaphthalen-4a-ol, allows methyl migration to compete with 1,2-elimination.

Benzoyl and Hydroxybenzoyl Esters of Coenzyme A: ULTRAVIOLET CHARACTERIZATION AND REACTION MECHANISMS

Abstract The ultraviolet spectra of purified benzoyl-CoA, o-hydroxybenzoyl-CoA, m-hydroxybenzoyl-CoA, and p-hydroxybenzoyl-CoA were studied and the esterolytic reactions of these compounds were investigated at alkaline pH in the absence and presence of certain amino acids. Besides a major absorption band at 261 to 262 nm, the spectrum of each hydroxybenzoyl thioester near neutral pH contains a longer wavelength absorption band (corresponding to the phenolic moiety) which undergoes a progressive red shift of 40 to 45 nm as the pH is raised. Approximate pKa values determined for the phenolic groups at room temperature are 9.5 for o- and m-hydroxybenzoyl-CoA and 8.6 for p-hydroxybenzoyl-CoA. At high pH, difference spectra (i.e. before esterolysis minus after) of all thioesters except p-hydroxybenzoyl-CoA reveal thioester absorbance at 269 to 273 nm with emm ranging from 6.4 to 6.9. Rates of esterolysis of benzoyl-CoA, m-hydroxybenzoyl-CoA, and p-hydroxybenzoyl-CoA are directly proportional to hydroxide ion concentration and approximate apparent second order rate constants at 38° are 10, 1.8, and 0.11 m-1 min-1, respectively. In contrast, the rate of esterolysis of o-hydroxybenzoyl-CoA is essentially constant, i.e. the apparent pseudo-first order rate constant is ∼0.02 min-1, over a pH range of 9.6 to 12.1. The postulated mechanisms are that with all the benzoyl-CoAs except o-hydroxybenzoyl-CoA, hydroxide ions participate in a nucleophilic attack on the carbonyl carbon of the benzoate moiety; with o-hydroxybenzoyl-CoA, the neighboring oxy anion repels close approach of hydroxide ion and instead acts as a general base to form the hydroxyl nucleophile in situ by removing a proton from water. This conclusion is supported by the additional finding that at pH 9.54 and 38°, o-hydroxybenzoyl-CoA reacts rapidly with several amino acids (glycine, d- and l-alanine, l-valine, l-asparagine, and l-glutamine) to form salicylpeptides. Under these conditions glycine reacts more rapidly with o-hydroxybenzoyl-CoA than with benzoyl-CoA or p-hydroxybenzoyl-CoA. Glycine is also a more effective nucleophile than hydroxide ion for o-hydroxybenzoyl-CoA, whereas the opposite is true for benzoyl-CoA or p-hydroxybenzoyl-CoA.