Following the discussion here of Kekulé’s suggestion of what we now call a vibrational mode (and which in fact now bears his name), I thought I might apply the concept to a recent molecule known as [2.2]paracyclophane.

In the preceding post, a nice discussion broke out about Kekulé’s 1872 model for benzene.[cite]10.1002/jlac.18721620110[/cite] This model has become known as the oscillation hypothesis between two extreme forms of benzene (below). The discussion centered around the semantics of the term oscillation compared to vibration (a synonym or not?) and the timescale implied by each word.

Continuing my european visits, here are two photos from Bonn. First, a word about how the representation of benzene evolved, attributed to Kekulé. The sausage formula Above is his first effort, made in 1865. The bent bond formula This one above is better, offered in 1866.

Not a computer in sight! I refer to a chemistry lab from the 1800s I was recently taken to, where famous french chemists such as Joseph Gay-Lussac, Michel Chevreul and Edmond Fremy were professors. Although not used for chemistry any more, it is an incredible treasure trove of objects. Here are photos of some.

I remember a time when tracking down a particular property of a specified molecule was an all day effort, spent in the central library (or further afield). Then came the likes of STN Online (~1980) and later Beilstein. But only if your institution had a subscription.

My name is displayed pretty prominently on this blog, but it is not always easy to find out who the real person is behind many a blog. In science, I am troubled by such anonymity.

This is rather cranking the handle, but taking my previous post and altering the search definition of the crystal structure database from 4- to 5-coordinate metals, one gets the following. Fe … Co … Ni … Cu … Trigonal bipyramidal coordination has angles of 90, 120 and 180°. Square pyramidal has no 120° angles, and the 180° angles might be somewhat reduced.

I love experiments where the insight-to-time-taken ratio is high. This one pertains to exploring the coordination chemistry of the transition metal region of the periodic table; specifically the tetra-coordination of the series headed by Mn-Ni. Is the geometry tetrahedral, square planar, or other? One can get a statistical answer in about ten minutes. The (CCDC database) search definition required is shown above.

Ribulose-1,5-bisphosphate reacts with carbon dioxide to produce 3-keto-2-carboxyarabinitol 1,5-bisphosphate as the first step in the biochemical process of carbon fixation.

I have just noticed unexpected links between two old posts, one about benzene, one about diphenyl magnesium and a link to August Kekulé. ^† Click for 3D The post about benzene dealt with the apparently simple issue of why all the C-C bonds are of equal length. The answer, in brief is purely because of the σ-electrons. If the π-electrons had their way, benzene would have three short and three long C-C bonds.

The journal of chemical education can be a fertile source of ideas for undergraduate student experiments. Take this procedure for asymmetric epoxidation of an alkene.[cite]10.1021/ed077p271[/cite] When I first spotted it, I thought not only would it be interesting to do in the lab, but could be extended by incorporating some modern computational aspects as well.