One of the delights of wandering around an undergraduate chemistry laboratory is discussing the unexpected, if not the outright impossible, with students. The >100% yield in a reaction is an example. This is sometimes encountered (albeit only briefly) when students attempt to recrystallise a product from cyclohexane, and get an abundant crop of crystals when they put their solution into an ice-bath to induce the crystallisation. Of the solvent of course! I should imagine 1000% yields are possible like this.
The melting points from benzene to cyclohexane: a prime example of dispersion forces in action?
December 30th, 2010Do marauding electrons go in packs?
December 27th, 2010Is there a preferred pack size for electrons on the move? Or put less flamboyantly, is there an optimum, and a maximum number of arrows (electron pairs) that one might push in revealing the mechanism of a concerted reaction? A sort of village-instinct for electrons. Consider the following (known, DOI: 10.1016/S0040-4039(00)98289-3) reaction
Embedding molecules in blogs: ChemDoodle, WebGL and SVG
December 24th, 2010If you get a small rotatable molecule below, then ChemDoodle/HTML5/WebGL is working. Why might this be important? Well, the future is mobile, in other words, devices that rely on batteries or other sources of built-in power. This means the power guzzling GPU cards of the past (some reach ~400 Watts!) cannot be used. Rather than using e.g. a full power OpenGL library, one will use Web-based graphics libraries, which (to quote Wikipedia) extends the capability of the JavaScript programming language to allow it to generate interactive 3D graphics within any compatible web browser. A typical target device might be for example Apple’s iPad (for which the redoubtable Jmol, which is based on Java, is unlikely to ever work).
(re)Use of data from chemical journals.
December 22nd, 2010If you visit this blog you will see a scientific discourse in action. One of the commentators there notes how they would like to access some data made available in a journal article via the (still quite rare) format of an interactive table, but they are not familiar with how to handle that kind of data (file). The topic in question deals with various kinds of (chemical) data, including crystallographic information, computational modelling, and spectroscopic parameters. It could potentially deal with much more. It is indeed difficult for any one chemist to be familiar with how data is handled in such diverse areas. So I thought I would put up a short tutorial/illustration in this post of how one might go about extracting and re-using data from this one particular source.
Following one’s nose: a quadruple bond to carbon. Surely I must be joking!
December 16th, 2010Do you fancy a story going from simplicity to complexity, if not absurdity, in three easy steps? Read on! The following problem appears in one of our (past) examination questions in introductory organic chemistry. From relatively mundane beginnings, one can rapidly find oneself in very unexpected territory.
Janus mechanisms (the past and the future): Reactions of the diazonium cation.
December 11th, 2010Janus was the mythological Roman god depicted as having two heads facing opposite directions, looking simultaneously into the past and the future. Some of the most ancient (i.e. 19th century) known reactions can be considered part of a chemical mythology; perhaps it is time for a Janus-like look into their future.
(anti)aromaticity avoided: a tutorial example
December 7th, 2010More inspiration from tutorials. In a lecture on organic aromaticity, the 4n+2/4n Hückel rule was introduced (in fact, neither rule appears to have actually been coined in this form by Hückel himself!). The simplest examples are respectively the cyclopropenyl cation and anion. The former has 2 π-electrons exhibiting cyclic delocalisation, and the 4n+2 (n=0) rule predicts aromaticity. Accordingly, all three C-C distances are the same (1.363Å).