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Henry Rzepa's Blog

Henry Rzepa's Blog
Chemistry with a twist
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Chemists now use the term “curly arrows” as a language to describe the electronic rearrangements that occur when a (predominately organic) molecule transforms to another – the so called chemical reaction. It is also used to infer, via valence bond or resonance theory, what the mechanistic implications of that reaction are.

Published

I have written a few times about the so-called “anomeric effect”, which relates to stereoelectronic interactions in molecules such as sugars bearing a tetrahedral carbon atom with at least two oxygen substituents. The effect can be detected when the two C-O bond lengths in such molecules are inspected, most obviously when one of these bonds has a very different length from the other.

Published

Respiratory pigments are metalloproteins that transport O 2 , the best known being the bright red/crimson coloured hemoglobin in human blood. The colour derives from Fe 2+ at the core of a tetraporphyrin ring. But less well known is blue blood , and here the colour derives from an oxyhemocyanin unit based on Cu 1+ (the de-oxy form is colourless) rather than iron.

Published

Four-coordinate carbon normally adopts a tetrahedral shape, where the four angles at the carbon are all 109.47°. But how large can that angle get, and can it even get to be 180°? A search of the CSD (crystal structure database) reveals a spiropentane as having the largest such angle, VAJHAP with 164°[cite]10.1021/ja00186a058[/cite] Because crystal structures might have artefacts such as disorder etc, it is always good to check this with a