Internal Hydroxyl Research Articles

ChemInform Abstract: C(2)‐Stereocontrol of δ‐Lactones via Acid‐Catalyzed Cyclization of Ketene Dithioacetal having an Internal Hydroxyl Group.

AbstractThe ketene dithioacetal derivatives (I) are hydrolyzed by HCl in different solvents to yield the spirocyclic dithio ketals (II).

C(2)-stereocontrol of δ-lactones [formula omitted] acid-catalyzed cyclization of ketene dithioacetal having an internal hydroxyl group

Stereocontrol of C(2)-position of δ-lactones, related to Prelog-Djerassi lactone, is effected via acid-catalyzed cyclization of ketene dithioacetal having an internal OH group (thermodynamic control), which is also applicable to remote asymmetric induction.

Combined catalytic and infrared study of the modification of H-ZSM-5 with selected poisons to give high p-xylene selectivity

The methylation of toluene with methanol has been compared over unmodified Zeolite HZSM-5 and over HZSM-5 samples that were partially or fully poisoned with preadsorbed quinoline or trimethylphosphite (TMP). The hydroxyl stretching region of the HZSM-5 zeolites was examined using infrared spectroscopy. Application of this technique to unmodified HZSM-5 showed that exposure to D 2O vapor caused deuteration of both the internal hydroxyls (3605 cm −1) and the external hydroxyls (3740 cm −1). Quinoline was shown to react with only the external hydroxyls whereas TMP reacted with and poisoned both the internal and external hydroxyls when adsorbed at room temperature. Desorption of quinoline was accompanied by dehydroxylation. Studies with a continuous-flow microcatalytic reactor demonstrated that HZSM-5 samples modified by preadsorption with quinoline or TMP prior to measurement of the activity profiles for alkylation exhibited diminished catalytic activity relative to unmodified HZSM-5 samples. However, they showed increased selectivity toward xylenes and toward p-xylene in particular. High para selectivity is attributed to the selective poisoning of the surface hydroxyls. TMP was found to be the more efficient poisoning agent and yielded the higher para selectivity, which is explicable in terms of more effective reaction with the surface hydroxyls.

ChemInform Abstract: DEUTERON QUADRUPOLE COUPLING IN HYDROGEN BONDED SYSTEMS. IV. DEUTERON QUADRUPOLE COUPLING IN SUBSTITUTED PHENOLS

AbstractDas NQR‐Spektrum von Deuterium am Phenol‐Sauerstoff wurde für die chlorierten Phenole 2‐, 3‐, 4‐Chlor‐phenol, 2,3‐, 2,4‐, 2,5‐, 2,6‐, 3,4‐, 3,5‐Dichlor‐phenol, 2,4,6‐Trichlor‐pheno1 sowie für 2,4‐Dimethyl‐ phenol aufgenommen.

Deuteron quadrupole coupling in hydrogen bonded systems. IV. Deuteron quadrupole coupling in substituted phenols

The pure nuclear quadrupole spectrum of deuterium at oxygen in chlorinated phenols has been observed by level crossing double resonance with the ring protons. Observed coupling constants, ranging from 200 to 250 kHz, exhibit the effects of strong hydrogen bonding through their correlation with the intermolecular O–H⋅⋅⋅O bond lengths in those cases where structure data are available. This is interpreted below to indicate that a primary effect of chlorine substitution is the influence it exerts on intermolecular hydrogen bonding through modification of the barrier to hydroxyl group rotation. From an extrapolation of the observed distance dependence, one may obtain a coupling constant of ∼283 kHz for deuterium at the oxygen position in non-hydrogen-bonded phenol. An interpretation of these data is made using model calculations on phenol, vinyl alcohol, and chlorovinyl alcohol. Barriers to internal rotation, as well as the dependence of the deuterium quadrupole coupling constant on the orientation of the –OD bond with respect to the ring plane are reported using a standard STO-4/31G basis. A value of 299 kHz is obtained for the deuterium coupling constant in the gas phase by interpolation from STO-4/31G calculations and gas phase data for water, methanol, and formic acid. Calculation demonstrates that the coupling constant of deuterium is essentially independent of –OD twist angle in phenol, and that vinyl alcohol is an excellent model fragment for phenol insofar as deuterium field gradients are concerned. Chlorovinyl alcohol exhibits a substantially larger barrier to internal –OD rotation than phenol, and also shows a weak dependence of field gradient on twist angle. Since solid phenol and substituted phenols show substantial deviations of the aromatic ring and –OD group from coplanarity, one may rationalize trends in the coupling constants on the basis of a modification of the barrier to internal hydroxyl group rotation by chlorine substitution. Attempts were made to obtain spectra in methyl- and bromo-substituted phenols, but with the exception of 2,4-dimethylphenol, low field relaxation times were too short to permit their observation.

Internal hydroxyl groups near the surface of silica

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInternal hydroxyl groups near the surface of silicaR. H. DoremusCite this: J. Phys. Chem. 1971, 75, 20, 3147–3148Publication Date (Print):September 1, 1971Publication History Published online1 May 2002Published inissue 1 September 1971https://doi.org/10.1021/j100689a019RIGHTS & PERMISSIONSArticle Views118Altmetric-Citations23LEARN 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 (232 KB) Get e-Alerts

The porous structure of self-supporting pressed silica discs: I. Infrared spectroscopic studies

Infrared Spectroscopic studies of a range of silicas prepared from an Aerosil show that the 3650-cm −1 absorption band present in the spectrum of silica gels corresponds to the regions of interparticle contact within the gel matrix. A comparison of the spectra of powder silicas and the corresponding self-supporting pressed discs suggests that the latter possesses a microporous gel structure. The reactions of the silicas with heavy water and boron trichloride vapor show that it is not possible to differentiate at all accurately between bulk or internal hydroxyls and surface hydroxyls in silica gel structures by hydrogen/deuterium isotopic exchange methods using heavy-water vapor as the exchanging agent.

The Concept of Internal pH in Wool Fibres and the Interpretation of Data Relating to Setting

A system consisting of wool fibres immersed in a salt solution has been considered in terms of the Donnan theory and an expression obtained which relates the hydroxyl–ion concentration of the ‘internal solution’ to the pH and salt concentration in the external solution, the affinities of hydroxyl ion, cation, and anion for the fibre, and the numbers of ionisable cationic and anionic groups in the fibre. This showed that at constant external pH and ionic strength, the internal hydroxyl–ion concentration would be increased by increasing the number of ionised cationic groups on the fibre, by adsorption of cations, or by decreasing the number of ionised anionic groups on the fibre. It would be decreased by adsorption of anionic groups. The effects of several chemical modifications of wool fibres on their setting properties can be explained in terms of their effects on the internal hydroxyl–ion concentration.