Posts Tagged ‘Bases’
Wednesday, May 11th, 2016
I have previously commented on the Bürgi–Dunitz angle, this being the preferred approach trajectory of a nucleophile towards the electrophilic carbon of a carbonyl group. Some special types of nucleophile such as hydrazines (R2N-NR2) are supposed to have enhanced reactivity[cite]10.1016/S0040-4020(01)93101-1[/cite] due to what might be described as buttressing of adjacent lone pairs. Here I focus in on how this might manifest by performing searches of the Cambridge structural database for intermolecular (non-bonded) interactions between X-Y nucleophiles (X,Y= N,O,S) and carbonyl compounds OC(NM)2.
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Tags:Bases, Bürgi–Dunitz angle, Carbonyl, Electrophile, Ester, Flippin–Lodge angle, Functional groups, hydrazine, non-metal attachments, Nucleophile, Physical organic chemistry, search query, Superbase
Posted in Chemical IT, crystal_structure_mining | 1 Comment »
Friday, April 15th, 2016
In the previous post I described how hydronium hydroxide or H3O+…HO–, an intermolecular tautomer of water, has recently been observed captured inside an organic cage[cite]10.1002/chem.201406383[/cite] and how the free-standing species in water can be captured computationally with the help of solvating water bridges. Here I explore azane oxide or H3N+-O–,‡ a tautomer of the better known hydroxylamine (H2N-OH).
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Tags:Ammonia, aqueous solutions, Bases, energy relative, free energy, Functional groups, Hydrogen bond, Hydronium, Hydroxides, Hydroxyl, Hydroxylamine, lowest energy form, Properties of water, Reducing agents, Self-ionization of water
Posted in General, Interesting chemistry | No Comments »
Friday, April 8th, 2016
Previously, I looked at models of how ammonia could be protonated by water to form ammonium hydroxide. The energetic outcome of my model matched the known equilbrium in water as favouring the unprotonated form (pKb ~4.75). I add here two amines for which R=Me3Si and R=CN. The idea is that the first will assist nitrogen protonation by stabilising the positive centre and the second will act in the opposite sense; an exploration if you like of how one might go about computationally designing a non-steric superbasic amine that becomes predominantly protonated when exposed to water (pKb <1)† and is thus more basic than hydroxide anion in this medium.
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Tags:Acid, Acid dissociation constant, Amide, Amine, Ammonia, Ammonium, Bases, City: Cambridge, energy, from non-protic solution, Functional groups, Hydrogen bond, Hydroxide, Lone pair, metal, Nitrile, relative free energy, search query
Posted in General, Interesting chemistry | 2 Comments »
Sunday, March 20th, 2016
This is a corollary to the previous post‡ exploring how many molecules are needed to ionise HCl. Here I am asking how many water molecules are required to form the ionic ammonium hydroxide from ammonia and water.
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Tags:Ammonia, Ammonium, Ammonium hydroxide, Bases, dilute solutions, free energy difference, Hydroxides, Ion, Properties of water
Posted in General | No Comments »
Thursday, January 7th, 2016
This is the third and final study deriving from my Ph.D.[cite]10.1039/P29750001822[/cite]. The first two topics dealt with the mechanism of heteroaromatic electrophilic attack using either a diazonium cation or a proton as electrophile, followed by either proton abstraction or carbon dioxide loss from the resulting Wheland intermediate. This final study inverts this sequence by starting with the proton abstraction from an indolinone by a base to create/aromatize to a indole-2-enolate intermediate, which only then is followed by electrophilic attack (by iodine). Here I explore what light quantum chemical modelling might cast on the mechanism.
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Tags:Arenium ion, Bases, diazo, Diazonium compound, Electrophile, Electrophilic aromatic substitution, Equilibrium chemistry, Fortran, Indole, light quantum chemical modelling, Metal ions in aqueous solution, Nuclear physics, Simple aromatic rings, Solutions
Posted in Historical, reaction mechanism | No Comments »