The Pirkle reagent is a 9-anthranyl derivative (X=OH, Y=CF3). The previous post on the topic had highlighted DIST1, the separation of the two hydrogen atoms shown below. The next question to ask is how general this feature is. Here we take a look at the distribution of lengths found in the Cambridge data base, and focus on another interesting example.
The inner secrets of an ion-pair: Isobornyl chloride rearrangements.
May 29th, 2011Observation of the slow racemization of isobornyl chloride in a polar solvent in 1923-24 by Meerwein led to the recognition that mechanistic interpretation is the key to understanding chemical reactivity. The hypothesis of ion pairs in which a chloride anion is partnered by a carbocation long ago entered the standard textbooks (see DOI 10.1021/ed800058c and 10.1021/jo100920e for background reading). But the intimate secrets of such ion-pairs are still perhaps not fully recognised. Here, to tease some of them them out, I use the NCI method, which has been the subject of several recent posts.
Blogs, Twitter, Wikis and other on-line tools: the movie!
May 27th, 2011Libraries (and librarians) are evolving rapidly. Thus a week or so ago one of our dynamic librarians here, approached some PhD students and academics to ask them how they used “Web 2.0” (thanks Jenny!). The result was edited (thanks John!) and uploaded, where you can see it below (embedded in this post, I might add, using HTML5). No doubt there is more of this genre to come. Libraries nowadays it seems, are not just about books and journals, but about the full digital experience (not to mention sustenance; ours is now one of the more popular places for students to eat!).
Déjà vu: Pirkle for a third time!
May 25th, 2011This molecule is not leaving me in peace. It and I first met in 1990 (DO: 10.1039/C39910000765), when we spotted the two unusual π-facial bonds formed when it forms a loose dimer. The next step was to use QTAIM to formalise this interaction, and this led to spotting a second one missed the first time round (labelled 2 in that post). Then a method known as NCI was tried, which revealed an H…H interaction, labelled ? in that post! Here I discuss the origins of the ?
The inner secrets of the DNA structure.
May 18th, 2011In earlier posts, I alluded to what might make DNA wind into a left or a right-handed helix. Here I switch the magnification of our structural microscope up a notch to take a look at some more inner secrets.
Updating a worked problem in conformational analysis. Part 2: an answer.
May 17th, 2011The previous post set out a problem in conformational analysis. Here is my take, which includes an NCI (non-covalent interaction) display as discussed in another post.
Updating a worked problem in conformational analysis. Part 1: the question.
May 13th, 2011Conformational analysis comes from the classical renaissance of physical organic chemistry in the 1950s and 60s. The following problem is taken from E. D. Hughes and J. Wilby J. Chem. Soc., 1960, 4094-4101, DOI: 10.1039/JR9600004094, the essence of which is that Hofmann elimination of a neomenthyl derivative (C below) was observed as anomalously faster than its menthyl analogue. Of course, what is anomalous in one decade is a standard student problem (and one Nobel prize) five decades later.
Nobelocene: a (hypothetical) 32-electron shell molecule?
April 29th, 2011The two previous posts have explored one of the oldest bonding rules (pre-dating quantum mechanics), which postulated that filled valence shells in atoms forming molecules follow the magic numbers 2, 8, 18 and 32. Of the 59,025,533 molecules documented at the instant I write this post, only one example is claimed for the 32-electron class. Here I suggest another, Nobelocene (one which given the radioactive instability of nobelium, is unlikely to be ever confirmed experimentally!)