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Henry Rzepa's Blog

Henry Rzepa's Blog
Chemistry with a twist
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Chemical ITCrystal_structure_miningAlkeneBürgi–Dunitz AngleCarbonylChemical Sciences
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The Bürgi–Dunitz angle is one of those memes that most students of organic chemistry remember. It hypothesizes the geometry of attack of a nucleophile on a trigonal unsaturated (sp 2 ) carbon in a molecule such as ketone, aldehyde, ester, and amide carbonyl.

Chemical ITAuthorChemical InformationDigital Object IdentifierThe JCE JournalChemical Sciences
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Blogging in chemistry remains something of a niche activity, albeit with a variety of different styles. The most common is commentary or opinion on the scientific literature or conferencing, serving to highlight what their author considers interesting or important developments. There are even metajournals that aggregate such commentaries. The question therefore occasionally arises;

Reaction MechanismAllotropyBromineCarbonChemical ElementsChemical Sciences
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Allotropes are differing structural forms of the elements. The best known example is that of carbon, which comes as diamond and graphite, along with the relatively recently discovered fullerenes and now graphenes. Here I ponder whether any of the halogens can have allotropes. Firstly, I am not aware of much discussion on the topic.

Chemical ITChemoinformaticsGeorge OrwellGravatarJournal Submission SystemsChemical Sciences
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Egon has reminded us that adoption of ORCID (Open researcher and collaborator ID) is gaining apace. It is a mechanism to disambiguate (a Wikipedia term!) contributions in the researcher community and to also remove much of the anonymity (where that is undesirable) that often lurks in social media sites.

Chemical ITCrystal_structure_miningAbove SearchAromatic CompoundsAromaticityChemical Sciences
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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.

Reaction MechanismAqueous SolutionChemical BondChemical BondingChemistryChemical Sciences
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Sodium 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. Initially, I am using Li, not Na (X=Li), to enable a more or less equal comparison with LAH, with water molecules to solvate rather than ether (n=2,3,5) and R set to Me.

Chemical ITAPIRCSB Protein Data BankSearch EngineChemical Sciences
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Last 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.

Reaction MechanismAl-H-Li BridgeDihydrocinnamyl Alcohol Reduction ProductFree EnergyImperial CollegeChemical Sciences
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The reduction of cinnamaldehyde by lithium aluminium hydride (LAH) was reported in a classic series of experiments[cite]10.1021/ja01197a060[/cite],[cite]10.1021/ja01202a082[/cite],[cite]10.1021/ja01190a082[/cite] dating from 1947-8. The reaction was first introduced into the organic chemistry laboratories here at Imperial College decades ago, vanished for a short period, and has recently been reintroduced again. The experiment is

Interesting ChemistryMt. EverestScientistChemical Sciences
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This 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.

Interesting ChemistryFree EnergyGas PhaseSteel WheelChemical Sciences
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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;