Posts Tagged ‘Electrophile’

Exploring the electrophilic directing influence of heteroaromatic rings using crystal structure data mining.

Tuesday, June 21st, 2016
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This is a follow-up to the post on exploring the directing influence of (electron donating) substituents on benzene[1] with the focus on heteroaromatic rings such indoles, pyrroles and group 16 analogues (furans, thiophenes etc).

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References

  1. H.S. Rzepa, "Discovering More Chemical Concepts from 3D Chemical Information Searches of Crystal Structure Databases", Journal of Chemical Education, vol. 93, pp. 550-554, 2015. http://dx.doi.org/10.1021/acs.jchemed.5b00346

What is the approach trajectory of enhanced (super?) nucleophiles towards a carbonyl group?

Wednesday, May 11th, 2016
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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[1] 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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References

  1. G. Klopman, K. Tsuda, J. Louis, and R. Davis, "Supernucleophiles—I", Tetrahedron, vol. 26, pp. 4549-4554, 1970. http://dx.doi.org/10.1016/S0040-4020(01)93101-1

I’ve started so I’ll finish. The ionisation mechanism and kinetic isotope effects for 1,3-dimethylindolin-2 one

Thursday, January 7th, 2016
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This is the third and final study deriving from my Ph.D.[1]. 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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References

  1. B.C. Challis, and H.S. Rzepa, "Heteroaromatic hydrogen exchange reactions. Part VIII. The ionisation of 1,3-dimethylindolin-2-one", Journal of the Chemical Society, Perkin Transactions 2, pp. 1822, 1975. http://dx.doi.org/10.1039/P29750001822

A new way of exploring the directing influence of (electron donating) substituents on benzene.

Friday, April 17th, 2015
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The knowledge that substituents on a benzene ring direct an electrophile engaged in a ring substitution reaction according to whether they withdraw or donate electrons is very old.[1] Introductory organic chemistry tells us that electron donating substituents promote the ortho and para positions over the meta. Here I try to recover some of this information by searching crystal structures.

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References

  1. H.E. Armstrong, "XXVIII.—An explanation of the laws which govern substitution in the case of benzenoid compounds", J. Chem. Soc., Trans., vol. 51, pp. 258-268, 1887. http://dx.doi.org/10.1039/CT8875100258