My previous post related to the aromatic electrophilic substitution of benzene using as electrophile phenyl diazonium chloride. Another prototypical reaction, and again one where benzene is too inactive for the reaction to occur easily, is the catalyst-free bromination of benzene to give bromobenzene and HBr.
Archive for the ‘Interesting chemistry’ Category
A congruence of concepts: conformations, configurations, amides and enzymes
Sunday, February 9th, 2014This is the time of year when I deliver two back-2-back lecture courses, and yes I do update and revise the content! I am always on the look-out for nice new examples that illustrate how concepts and patterns in chemistry can be joined up to tell a good story. My attention is currently on conformational analysis; and here is an interesting new story to tell about it.
Three-for-one: a pericyclic brain teaser.
Sunday, January 12th, 2014A game one can play with pericyclic reactions is to ask students to identify what type a given example is. So take for example the reaction below.
Does forming a Wheland intermediate disrupt all aromaticity?
Friday, December 6th, 2013Text books will announce that during aromatic electrophilic substitution, aromaticity is lost by the formation of a Wheland intermediate (and regained by eliminating a proton). Is that entirely true?
Multiple personalities of Magnesium.
Tuesday, November 5th, 2013The following is a short question in a problem sheet associated with introductory organic chemistry.
The world ash tree of the computer hardware industry… crystalline silicon from 1854.
Thursday, October 31st, 2013The element silicon best represents the digital era of the mid 20th century to the present; without its crystalline form, there would be no computers (or this blog). Although it was first prepared in pure amorphous (powder) form around 1823[1] by Berzelius, it was not until 1854 that Henri Sainte-Claire Deville made it in crystalline form, using metallic aluminium to isolate it. He described it [1] as having a “metallic luster”.
References
Six vs ten aromatic electrons?
Sunday, October 20th, 2013Homoaromaticity is a special case of aromaticity in which π-conjugation is interrupted by a single sp3 hybridized carbon atom (it is sometimes referred to as a suspended π-bond with no underlying σ-foundation). But consider the carbene shown below. This example comes from a recently published article[1] which was highlighted on Steve Bachrach’s blog. Here aromaticity has resulted from a slightly different phenomenon, whereby a 4π-electron planar (and hence nominally anti-aromatic) molecule is elevated to aromatic peerage by promoting the two carbene σ-electrons to have π-status.
References
- B. Chen, A.Y. Rogachev, D.A. Hrovat, R. Hoffmann, and W.T. Borden, "How to Make the σ<sup>0</sup>π<sup>2</sup> Singlet the Ground State of Carbenes", Journal of the American Chemical Society, vol. 135, pp. 13954-13964, 2013. https://doi.org/10.1021/ja407116e