The knowledge that substituents on a benzene ring direct an electrophile engaged in a ring substitution reaction according to whether they withdraw or donate electrons is very old.[cite]10.1039/CT8875100258[/cite] Introductory organic chemistry tells us that electron donating substituents promote the ortho and para positions over the meta. Here I try to recover some of this information by searching crystal structures.
A new way of exploring the directing influence of (electron donating) substituents on benzene.
April 17th, 2015The mechanism of borohydride reductions. Part 1: ethanal.
April 12th, 2015Sodium borohydride is the tamer cousin of lithium aluminium hydride (LAH). It is used in aqueous solution to e.g. reduce aldehydes and ketones, but it leaves acids, amides and esters alone. Here I start an exploration of why it is such a different reducing agent.
Goldilocks Data.
April 8th, 2015Last August, I wrote about data galore, the archival of data for 133,885 (134 kilo) molecules into a repository, together with an associated data descriptor[cite]10.1038/sdata.2014.22[/cite] published in the new journal Scientific Data. Since six months is a long time in the rapidly evolving field of RDM, or research data management, I offer an update in the form of some new observations.
Ionizing yet more ultra-strong acids with water molecules.
March 20th, 2015This might be seen as cranking a handle by producing yet more examples of acids ionised by a small number of water molecules. I justify it (probably only to myself) as an exercise in how a scientist might approach a problem, and how it linearly develops with time, not necessarily in the directions first envisaged. A conventional scientific narrative published in a conventional journal tells the story often with the benefit of hindsight, but rarely how the project actually unfolded chronologically.‡ So by devoting 7 posts to this, you can judge for yourself how my thoughts might have developed (and I am prepared to acknowledge this may only serve to show my ignorance).
A 5-high straight flush of water-ionised acids?
March 17th, 2015I do not play poker,‡ and so I had to look up a 5-4-3-2-1(A), which Wikipedia informs me is a 5-high straight flush, also apparently known as a steel wheel. In previous posts I have suggested acids which can be ionised by (probably) 5, 4, 3 or 1 discrete water molecules in the gas phase; now to try to track down a candidate for ionisation by the required two water molecules to form that straight flush.
Ionizing ultra-strong acids with water molecules.
March 15th, 2015My previous posts have covered the ionization by a small number of discrete water molecules of the series of halogen acids, ranging from HI (the strongest, pKa -10) via HF (weaker, pKa 3.1) to the pseudo-halogen HCN (the weakest, pKa 9.2). Here I try out some even stronger acids to see what the least number of water molecule needed to ionize these might be.
How many water molecules does it take to ionise HCN/HNC? An NCI exploration.
March 2nd, 2015HCN is a weak acid (pKa +9.2, weaker than e.g. HF), although it does have an isomer, isocyanic acid or HNC (pka < +9.2 ?) which is simultaneously stronger and less stable. I conclude my halide acid series by investigating how many water molecules (in gas phase clusters) are required for ionisation of this “pseudo-halogen” acid.
How many water molecules does it take to ionise HI?
February 28th, 2015Why is this post orphaned from the previous? In order to have the opportunity of noting that treating iodine computationally can be a little different from the procedures used for F, Cl and Br.