I 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.
Archive for the ‘Interesting chemistry’ Category
A 5-high straight flush of water-ionised acids?
Tuesday, March 17th, 2015Ionizing ultra-strong acids with water molecules.
Sunday, 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.
Monday, 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?
Saturday, February 28th, 2015How many water molecules does it take to ionise HF and HBr?
Friday, February 27th, 2015No doubt answers to the question posed in the previous post are already being obtained by experiment. Just in case that does not emerge in the next day or so, I offer a prediction here.
How many water molecules does it take to ionise HCl?
Saturday, February 14th, 2015According to Guggemos, Slavicek and Kresin, about 5-6![cite]10.1103/PhysRevLett.114.043401[/cite]. This is one of those simple ideas, which is probably quite tough to do experimentally. It involved blasting water vapour through a pinhole, adding HCl and measuring the dipole-moment induced deflection by an electric field. They found “evidence for a noticeable rise in the dipole moment occurring at n≈5–6“.
Chiroptical spectroscopy of the natural product Steganone.
Tuesday, February 10th, 2015Steganone is an unusual natural product, known for about 40 years now. The assignment of its absolute configurations makes for an interesting, on occasion rather confusing, and perhaps not entirely atypical story. I will start with the modern accepted stereochemical structure of this molecule, which comes in the form of two separately isolable atropisomers.
The first reported synthesis of this system in 1977 was racemic, and no stereochemistry is shown in the article (structure 2).[cite]10.1039/P19770001674[/cite] Three years later an “Asymmetric total synthesis of (-)steganone and revision of its absolute configuration” shows how the then accepted configuration (structure 1 in this article) needs to be revised to the enantiomer shown as structure 12 in the article[cite]10.1016/S0040-4039(00)78586-8[/cite] and matching the above representation. The system has continued to attract interest ever since[cite]10.1039/P19820000521[/cite],[cite]10.1039/A900743A[/cite],[cite]10.1039/C39950001943[/cite],[cite]10.1002/ejoc.201402761[/cite], not least because of the presence of axial chirality in the form of atropisomerism. Thus early on it was shown that the alternative atropisomer, the (aS,R,R) configuration initially emerges out of several syntheses, and has to be converted to the (aR,R,R) configuration by heating[cite]10.1039/P19820000521[/cite]. One could easily be fooled by such isomerism!
Fine-tuning a (hydrogen) bond into symmetry.
Friday, January 23rd, 2015Sometimes you come across a bond in chemistry that just shouts at you. This happened to me in 1989[cite]10.1039/C39890001722[/cite] with the molecule shown below. Here is its story and, 26 years later, how I responded.
Halogen bonds 4: The strongest (?) halogen bond.
Sunday, December 7th, 2014
Continuing my hunt, here is a candidate for a strong(est?) halogen bond, this time between Se and I.[cite]10.1021/ic50038a006[/cite]. 
The features of interest include:
Halogen bonds 3: “Nitrogen tri-iodide”
Monday, December 1st, 2014Nitrogen tri-iodide, or more accurately the complex between it and ammonia ranks amongst the oldest known molecules (1812). I became familiar with it around the age of 12-13, in an era long gone when boys (and very possibly girls too) were allowed to make such substances in their parent’s back gardens‡ and in fact in the school science laboratory,† an experiment which earned me a personal request to visit the head teacher.