87 research outputs found
Asymmetric Epoxidation: A Twinned Laboratory and Molecular Modeling Experiment for Upper-Level Organic Chemistry Students
The coupling of a student experiment
involving the preparation
and use of a catalyst for the asymmetric epoxidation of an alkene
with computational simulations of various properties of the resulting
epoxide is set out in the form of a software toolbox from which students
select appropriate components. At the core of these are the computational
spectroscopic tools, whereby a measured spectrum can be interpreted
in some detail using theoretical simulations. These include a range
of modern chiroptical methods to accompany the increased use of such
techniques in modern teaching laboratories. Computational experiments
are captured in a Wiki-based electronic laboratory notebook, which
features data-stamping, authenticated entries, and inclusion of semantically
intact data via interactive models rendered within the Wiki using
JSmol and its referencing via a digital object identifier (DOI) to
a digital data repository
Non-catalytic bromination of benzene: a combined computational and experimental study
The non-catalytic bromination of benzene is shown experimentally to require high 5-14M concentrations of bromine in order to proceed at ambient temperatures to form predominantly bromobenzene, along with detectable (The non-catalytic bromination of benzene is shown experimentally to require high 5-14M concentrations of bromine in order to proceed at ambient temperatures to form predominantly bromobenzene, along with detectable (The non-catalytic bromination of benzene is shown experimentally to require high 5-14M concentrations of bromine in order to proceed at ambient temperatures to form predominantly bromobenzene, along with detectable
A metadata-driven approach to data repository design
The design and use of a metadata-driven data repository for research data management is described. Metadata is collected automatically during the submission process whenever possible and is registered with DataCite in accordance with their current metadata schema, in exchange for a persistent digital object identifier. Two examples of data preview are illustrated, including the demonstration of a method for integration with commercial software that confers rich domain-specific data analytics without introducing customisation into the repository itself
A stereoselective hydride transfer reaction with contributions from attractive dispersion force control
The experimentally determined stereochemical outcome of an unprecedented hydride transfer from a lithium alkoxide to an aldehyde is reported, as deconvoluted by the combined use of a single enantiomer alkoxide in conjunction with a deuterium label. The stereoselective outcome is consistent with a computationally predicted transition state model stabilised by contributions from attractive dispersion forces
Modulation of Amide Bond Rotamers in 5-Acyl-6,7-dihydrothieno[3,2-c]pyridines
2-Substituted <i>N</i>-acyl-piperidine
is a widespread
and important structural motif, found in approximately 500 currently
available structures, and present in nearly 30 pharmaceutically active
compounds. Restricted rotation of the acyl substituent in such molecules
can give rise to two distinct chemical environments. Here we demonstrate,
using NMR studies and density functional theory modeling of the lowest
energy structures of 5-acyl-6,7-dihydrothienoÂ[3,2-<i>c</i>]Âpyridine derivatives, that the amide <i>E</i>:<i>Z</i> equilibrium is affected by non-covalent interactions between
the amide oxygen and adjacent aromatic protons. Structural predictions
were used to design molecules that promote either the <i>E</i>- or <i>Z</i>-amide conformation, enabling preparation
of compounds with a tailored conformational ratio, as proven by NMR
studies. Analysis of the available X-ray data of a variety of published <i>N</i>-acyl-piperidine-containing compounds further indicates
that these molecules are also clustered in the two observed conformations.
This finding emphasizes that directed conformational isomerism has
significant implications for the design of both small molecules and
larger amide-containing molecular architectures
Pyrimidine nucleosides syntheses by late-stage base heterocyclization reactions
An efficient two-step procedure for the syntheses of pyrimidine nucleosides is presented. A series of glycosyl 5-(aminomethylene)-1,3-dioxane-4,6-dione derivatives were prepared from ÎČ-anomeric isonitriles by reaction with Meldrumâs acid or by allowing aminomethylene Meldrumâs acid to react with an 1-aldofuranosyl halide or acetate. The resultant 5-(aminomethylene)-1,3-dioxane-4,6-dione derivatives underwent reaction with benzyl- or 2,4-dimethoxybenzyl isocyanate via transacylation to provide uridine-5-carboxylic acid derivatives and related nucleosides. These nucleoside carboxylic acids were converted into other C-5 derivatives by bromo-decarboxylation with N-bromosuccinimide
Equilibrium Formation of Stable AllâSilicon Versions of 1,3âCyclobutanediyl
Main group analogues of cyclobutaneâ1,3âdiyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of allâsilicon 1,3âcyclobutanediyls as stable closedâshell singlet species from the reversible reactions of cyclotrisilene c âSi3Tip4 (Tip=2,4,6âtriisopropylphenyl) with the Nâheterocyclic silylenes c â[(CR2CH2)(Nt Bu)2]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated Nâheterocyclic silylene c â(CH)2(Nt Bu)2Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3âcyclobutanediyl intermediate
Surfing the Ï-clouds for Non-covalent Interactions: A comparative Study of Arenes versus Alkenes
A comparative study by NMR spectroscopy using molecular balances indicates that non-covalent functional group interactions with an arene dominate over those with an alkene and a p-facial intramolecular hydrogen bond from a hydroxyl group to an arene is favoured by ~1.2 kJ mol-1. The strongest interaction observed in this study is with the cyano group and analysis of the series of Et, CH=CH2, CâĄCH and CâĄN groups is indicative of a weak long range electrostatic interaction and a correlation with the electrophilicity of the Ca atom of the Y substituent. Changes in the free energy differences of conformers show a linear dependence on the solvent hydrogen bond acceptor parameter ÎČ
IUPAC specification for the FAIR management of spectroscopic data in chemistry (IUPAC FAIRSpec) - guiding principles
set of guiding principles for the development of a standard for FAIR management of spectroscopic data are outlined and discussed. The principles form the basis for future recommendations of IUPAC Project 2019-031-1-024 specifying a detailed data model and metadata schema for describing the contents of an âIUPAC FAIRData Collectionâ and the organization of digital objects within that collection. Foremost among the recommendations will be a specification for an âIUPAC FAIRData Finding Aidâ that describes the collection in such a way as to optimize the findability, accessibility, interoperability, and reusability of its contents. Results of an analysis of data provided by an American Chemical Society Publications pilot study are discussed in relation to potential workflows that might be used in implementing the âIUPAC FAIRSpecâ standard based on these principles
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