Posts Tagged ‘Ammonia’
Friday, March 10th, 2017
A few years back, I did a post about the Pirkle reagent[1] and the unusual π-facial hydrogen bonding structure[2] it exhibits. For the Pirkle reagent, this bonding manifests as a close contact between the acidic OH hydrogen and the edge of a phenyl ring; the hydrogen bond is off-centre from the middle of the aryl ring. Here I update the topic, with a new search of the CSD (Cambridge structure database), but this time looking at the positional preference of that bond and whether it is on or off-centre.
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References
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H.S. Rzepa, M.L. Webb, A.M.Z. Slawin, and D.J. Williams, "? Facial hydrogen bonding in the chiral resolving agent (S)-2,2,2-trifluoro-1-(9-anthryl)ethanol and its racemic modification", Journal of the Chemical Society, Chemical Communications, pp. 765, 1991. http://dx.doi.org/10.1039/c39910000765
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H.S. Rzepa, M.H. Smith, and M.L. Webb, "A crystallographic AM1 and PM3 SCF-MO investigation of strong OH ⋯π-alkene and alkyne hydrogen bonding interactions", J. Chem. Soc., Perkin Trans. 2, pp. 703-707, 1994. http://dx.doi.org/10.1039/P29940000703
Tags:Ammonia, Ammonium, aromaticity, Cations, Centroid, chemical bonding, Chemistry, Hydrogen bond, Phenyl group
Posted in crystal_structure_mining | No Comments »
Friday, April 15th, 2016
If H3N+-O– is viable compared with its tautomer H2N-OH when carrying water bridges, then why not try H2O+-O– vs HO-OH?
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Tags:Ammonia, Anions, free energy, General, Hydrogen bond, Hydrogen peroxide, Inorganic solvents, Interesting chemistry, Oxide, Oxidizing agents, Peroxide, Properties of water
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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[1] 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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References
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M. Stapf, W. Seichter, and M. Mazik, "Unique Hydrogen‐Bonded Complex of Hydronium and Hydroxide Ions", Chemistry – A European Journal, vol. 21, pp. 6350-6354, 2015. http://dx.doi.org/10.1002/chem.201406383
Tags:Ammonia, aqueous solutions, Bases, energy relative, free energy, Functional groups, General, Hydrogen bond, Hydronium, Hydroxides, Hydroxyl, Hydroxylamine, Interesting chemistry, lowest energy form, Properties of water, Reducing agents, Self-ionization of water
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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, General, Hydrogen bond, Hydroxide, Interesting chemistry, Lone pair, metal, Nitrile, relative free energy, search query
Posted in Uncategorised | 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, General, Hydroxides, Ion, Properties of water
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