The Möbius band is an experimental delight. In its original forms, it came flat-packed as below. The one shown on the left is related to the international symbol for recycling (if we denote the number of half twists imparted as m, this one has m=3). The middle one (m=4) shows a 4-twisted variant, and the one on the right has a 5-twist (m=5). These all come from Möbius’ original sketches, found amongst his belongings when he died. In this post they will form the basis for some experiments in molecular chirality.
Valentine chemistry
February 13th, 2011A short history of molecular modelling: 1860-1890.
February 5th, 2011In 1953, the model of the DNA molecule led to what has become regarded as the most famous scientific diagram of the 20th century. It had all started 93 years earlier in 1860, at a time when the tetravalency of carbon was only just established (by William Odling) and the concept of atoms as real entities was to remain controversial for another 45 years (for example Faraday, perhaps the most famous scientist alive in 1860 did not believe atoms were real). So the idea of constructing a molecular model from atoms as the basis for understanding chemical behaviour was perhaps bolder than we might think. It is shown below, part of a set built for August Wilhelm von Hofmann as part of the lectures he delivered at the Royal College of Chemistry in London (now Imperial College).
Shorter is higher: the strange case of diberyllium.
January 21st, 2011Much of chemistry is about bonds, but sometimes it can also be about anti-bonds. It is also true that the simplest of molecules can have quite subtle properties. Thus most undergraduate courses in chemistry deal with how to describe the bonding in the diatomics of the first row of the periodic table. Often, only the series C2 to F2 is covered, so as to take into account the paramagnetism of dioxygen, and the triple bonded nature of dinitrogen (but never mentioning the strongest bond in the universe!). Rarely is diberyllium mentioned, and yet by its strangeness, it can also teach us a lot of chemistry.
Is there a difference between a scientific blog and scientific journal?
January 14th, 2011In my blogroll, I link to Tim Gowers’ blog. He is a very eminent mathematician, and so it is interesting to see what motivates him to write a blog about mathematics. This latest post goes a large way to explaining why. He starts by speculating about the features of some piece of research that might render it conventionally unpublishable, highlighting two reasons; (1) it is not original and (2) it does not lead anywhere conclusive. He then goes on to show how either outcome might nevertheless be useful to someone, even if unpublishable conventionally. The rest of his post then concentrates on the cap-set problem in pure mathematics. It boils down to the observation that the community as a whole might often spot something that individual might have a blind spot for. Or, that others may in turn be inspired by lines of research which had apparently led nowhere for the original poster. Tim of course is favoured by having often 80+ comments appended to each of his posts!
A comparison of left and right handed DNA double-helix models.
January 1st, 2011When Watson and Crick (WC) constructed their famous 3D model for DNA, they had to decide whether to make the double helix left or right handed. They chose a right-handed turn, on the grounds that their attempts at left-handed models all “violated permissible van der Waals contacts“. No details of what these might have been were given in their original full article (or the particular base-pairs which led to the observation). This follow-up to my earlier post explores this aspect, using a computer model.
The melting points from benzene to cyclohexane: a prime example of dispersion forces in action?
December 30th, 2010One 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.
Do 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).