China
Africa
Explore chapters and articles related to this topic
Conformations
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
The bond angles in cyclobutane at about 90°, so there is less Baeyer strain, and the extra carbon when compared to cyclopropane gives the molecule more flexibility, so there is more pseudorotation to alleviate torsion strain. Is cyclohexane more or less flexible when compared to cyclopentane?
Predicting semiclathrate hydrates dissociation pressure using a rigorous machine learning approach
Published in Journal of Dispersion Science and Technology, 2020
Aminreza Hosseinzadeh, Abolfazl Mohammadi, Ebrahim Soroush
In order to moderate the hydrate formation conditions, use of kinetic and thermodynamic promoters is the most accepted method.[7–12] These additives help to reduce the induction time and the required hydrate formation pressure. In addition, they increase the storage capacity, the formation temperature and the rate of hydrate formation. The promoters influence on the selectivity of water cages for hosting gas molecules.[13] In general, there are two types of promoters.[13] The first group does not affect the structure of hydrate cages. The most famous promoters of this kind are tetrahydrofuran (THF), cyclobutane (CB), Oxolane, acetone, cyclohexane (CH), methylcyclohexane (MCH), cyclopentane (CP), cycloheptane (CHP), and methyl cyclopentane (MCP). Despite the effectiveness of these additives, they may cause some difficulties such as flammability, volatility, and toxicity.[14–16] The second group of hydrate promoters in particular tetra-n-butyl ammonium salts alters the ordinary structure of water cages and produce semiclathrate hydrates.[8,16–19]
The effect of structure and isomerism on the vapor pressures of organic molecules and its potential atmospheric relevance
Published in Aerosol Science and Technology, 2019
Caroline Dang, Thomas Bannan, Petroc Shelley, Michael Priestley, Stephen D. Worrall, John Waters, Hugh Coe, Carl J. Percival, David Topping
Compounds 3 has a lower vapor pressure than 1 and 2 due to the two carboxyl groups being located on the same carbon atom of the cyclobutane ring as opposed to on adjacent carbon atoms which increases the molecules effective dipole. A dipole is formed when a bond or functional group has an unequal distribution of electrons across it, usually due to the presence of electronegative atoms such as O, and results in the bond or functional group becoming polarized with a slight negative charge at one end and a slight positive charge at the other. The effective dipole of a molecule is the vector sum of the individual dipoles within it; a molecule with an effective dipole is able to interact electrostatically with other molecules that possess effective dipoles and this has the effect of supressing vapor pressure. Due to the smaller angle between the two carboxyl groups, which each possess an individual dipole, in 3 compared to 1 and 2 (Figure 5) its effective dipole moment is greater thus explaining its lower vapor pressure.
Synthesis of six- and seven-membered and larger heterocylces using Au and Ag catalysts
Published in Inorganic and Nano-Metal Chemistry, 2018
Indole is present in several different alkaloids. Their biological properties made them a target of special attention.[107–118] The (−)-mersicarpine is an alkaloid which exhibit an unusual tetracyclic structure and is isolated from Kopsia plants. The (−)-mersicarpine was prepared enantioselectively. The reaction of an alkynol-based intermediate with Au salt was proposed to be included in retrosynthetic analysis, although under these conditions only alkyne moiety was reactive and preserved the –OH moiety for subsequent oxidation.[119] A cascade reaction including both carbon-carbon and carbon-oxygen bond formation in the presence of Au salt catalyst has been established for the synthesis of 2,3-indoline-fused cyclobutane (non-natural skeleton).[120] Echavarren et al. reported an intra- and intermolecular reaction of alkynes and indoles with Au catalyst, such as starting from alkynol-based systems and alkynols, to afford carbazole-like systems and related structures (Scheme 44).[121]