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Henry Rzepa's Blog

Henry Rzepa's Blog
Chemistry with a twist
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Chemical ITCrystal_structure_miningChemistryChloroform SolutionsConformational IsomerismQuímicaInglês
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Conformational polymorphism occurs when a compound crystallises in two polymorphs differing only in the relative orientations of flexible groups ( e.g. Ritonavir).[cite]10.1039/D1SC06074K[/cite] At the Beilstein conference, Ian Bruno mentioned another type; ** tautomeric polymorphism**, where a compound can crystallise in two forms differing in the position of acidic protons. Here I explore three such examples.

Crystal_structure_miningCompany: CL ENGENHARIADerekDerek LoweLoweQuímicaInglês
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Derek Lowe highlights a recent article[cite]10.1002/anie.201702626[/cite] postulating CH⋅⋅⋅π interactions in proteins. Here I report a quick check using the small molecule crystal structure database (CSD). The search query (DOI: 10.14469/hpc/2594) is shown below.

Chemical ITAppletCompression AlgorithmComputingCross-platform SoftwareQuímicaInglês
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As the Internet and its Web-components age, so early pages start to decay as technology moves on. A few posts ago, I talked about the maintenance of a relatively simple page first hosted some 21 years ago. In my notes on the curation, I wrote the phrase “ Less successful was the attempt to include buttons which could be used to annotate the structures with highlights.

Crystal_structure_miningAlkeneAlkyneFunctional GroupsIntra-molecular SearchQuímicaInglês
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Following on from my re-investigation of close hydrogen bonding contacts to the π-face of alkenes, here now is an updated scan for H-bonds to alkynes. The search query (dataDOI: 10.14469/hpc/2478) is similar to the previous one: QA is any of N,O,F,Cl. X is any atom, including metals and non-metals.

Crystal_structure_miningCalculated EnergyChemical BondingChemistryCrystalQuímicaInglês
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Back in the early 1990s, we first discovered the delights of searching crystal structures for unusual bonding features.[cite]10.1039/P29940000703[/cite] One of the first cases was a search for hydrogen bonds formed to the π-faces of alkenes and alkynes. In those days the CSD database of crystal structures was a lot smaller (<80,000 structures; it’s now ten times larger) and the search software less powerful.

Crystal_structure_miningCarbonChemical BondingChemistryCyclopentadienyl AnionQuímicaInglês
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Layer stacking in structures such as graphite is well-studied. The separation between the π-π planes is ~3.35Å, which is close to twice the estimated van der Waals (vdW) radius of carbon (1.7Å). But how much closer could such layers get, given that many other types of relatively weak interaction such as hydrogen bonding can contract the vdW distance sum by up to ~0.8Å or even more?