The epoxidation of an alkene to give an oxirane is taught in introductory organic chemistry. Formulating an analogous mechanism for such reaction of an alkyne sounds straightforward, but one gradually realises that it requires raiding knowledge from several other areas of (perhaps slightly more advanced) chemistry to achieve a joined up approach to the problem.
Following on from Armstrong’s almost electronic theory of chemistry in 1887-1890, and Beckmann’s radical idea around the same time that molecules undergoing transformations might do so via a reaction mechanism involving unseen intermediates (in his case, a transient enol of a ketone) I here describe how these concepts underwent further evolution in the early 1920s.
Fascination with nano-objects, molecules which resemble every day devices, is increasing. Thus the world’s smallest car has just been built[cite]10.1038/nature10587[/cite]. The mechanics of such a device can often be understood in terms of chemical concepts taught to most students. So I thought I would have a go at this one!
Henry Armstrong studied at the Royal College of Chemistry from 1865-7 and spent his subsequent career as an organic chemist at the Central College of the Imperial college of Science and technology until he retired in 1912.
An attosecond is 10 -18 s. The chemistry that takes place on this timescale is called electron dynamics. For example, it is the time taken for an electron to traverse the 1s orbit in a hydrogen atom. And chemists are starting to manipulate electrons (and hence chemistry) on this timescale; for example a recent article (DOI: 10.1021/ja206193t) describes how to control the electrons in benzene using attosecond laser pulses.
How one might go about answering the question: do alkenes promote anomeric effects? A search of chemical abstracts does not appear to cite any examples (I may have missed them of course, since it depends very much on the terminology you use, and new effects may not yet have any agreed terminology) and a recent excellent review of hyperconjugation does not mention it. Here I show how one might provide an answer.
My previous post introduced the interesting guts of taxol. Two different isomers can exist, and these are called atropisomers; one has the carbonyl group pointing up, the other down. The barrier to their interconversion in this case is generated by a rotation about the two single bonds connecting the carbonyl group to the rest of the molecule.
Most of the chemical structure diagrams in this blog originate from Chemdraw, which seems to have been around since the dawn of personal computers! I have tended to use this program to produce JPG bitmaps for the blog, writing them out in 4x magnification, so that they can be scaled down for display whilst retaining some measure of higher resolution if needed for other purposes.
Moore’s law describes a long-term trend in the evolution of computing hardware, and it is often interpreted in terms of processing speed. Here I chart this rise in terms of the size of computable molecules. By computable I mean specifically how long it takes to predict the geometry of a given molecule using a quantum mechanical procedure. LSD, the 1975 benchmark for computable molecules.
My previous post on the topic of mauveine left the outcome dangling. Put simply, λ max is measured at about 549nm for mauveine A, but was calculated at about 440nm using a modern method for predicting colour (TD-DFT). According to the colour table below, that would make it orange, not mauve. Can the theoretical prediction be out by 110nm, or might it be the structure of the molecule itself that has been wrongly described?
As the title hints, I have been here before. The S N 1 solvolysis mechanism of t-butyl chloride was central to the flourishing of physical organic chemistry from the 1920s onwards, and it appears early on in most introductory lecture courses and text books. There we teach that it is a two-stage mechanism.