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Henry Rzepa's Blog

Henry Rzepa's Blog
Chemistry with a twist
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HypervalencyInteresting ChemistryHenry RzepaJahn-TellerPenceKimya Bilimleriİngilizce
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Do you fancy a story going from simplicity to complexity, if not absurdity, in three easy steps? Read on! The following problem appears in one of our (past) examination questions in introductory organic chemistry. From relatively mundane beginnings, one can rapidly find oneself in very unexpected territory. How would one make 3-nitrobenzonitrile?

Interesting ChemistryActivation Free EnergyBenzonitrile ProductChemical MythologyColoured SolutionsKimya Bilimleriİngilizce
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Janus was the mythological Roman god depicted as having two heads facing opposite directions, looking simultaneously into the past and the future. Some of the most ancient ( i.e. 19th century) known reactions can be considered part of a chemical mythology; perhaps it is time for a Janus-like look into their future. Reaction of the diazonium cation with cyanide.

Interesting ChemistryEnergyFree EnergyHuckelPretty Straight ForwardKimya Bilimleriİngilizce
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More inspiration from tutorials. In a lecture on organic aromaticity, the 4n+2/4n Hückel rule was introduced (in fact, neither rule appears to have actually been coined in this form by Hückel himself!). The simplest examples are respectively the cyclopropenyl cation and anion. The former has 2 π-electrons exhibiting cyclic delocalisation, and the 4n+2 (n=0) rule predicts aromaticity.

Interesting ChemistryAcyloxyboraneArrow PushingPost OperativeTutorKimya Bilimleriİngilizce
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Arrow pushing (why never pulling?) is a technique learnt by all students of organic chemistry (inorganic chemistry seems exempt!). The rules are easily learnt (supposedly) and it can be used across a broad spectrum of mechanism. But, as one both becomes more experienced, and in time teaches the techniques oneself as a tutor, its subtle and nuanced character starts to dawn.

Chemical ITAdobeAppleApple IPadChemDraw 12Kimya Bilimleriİngilizce
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For those of us who were around in 1985, an important chemical IT innovation occurred. We could acquire a computer which could be used to draw chemical structures in one application, and via a mysterious and mostly invisible entity called the clipboard , paste it into a word processor (it was called a Macintosh). Perchance even print the result on a laserprinter.

Interesting ChemistryChemistChiropticalPhysicistSynthetic ChemistKimya Bilimleriİngilizce
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Our understanding of science mostly advances in small incremental and nuanced steps (which can nevertheless be controversial) but sometimes the steps can be much larger jumps into the unknown, and hence potentially more controversial as well. More accurately, it might be e.g. relatively unexplored territory for say a chemist, but more familiar stomping ground for say a physicist.

Interesting ChemistryDavid ScheschkewitzIgor AlabuginPericyclicWatoc11Kimya Bilimleriİngilizce
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On 8th August this year, I posted on a fascinating article that had just appeared in Science[cite]10.1126/science.1188002[/cite] in which the crystal structure was reported of two small molecules, 1,3-dimethyl cyclobutadiene and carbon dioxide, entrapped together inside a calixarene cavity.

Interesting ChemistryAndrew WhiteChemical Heritage CollectionsDetectiveHistoricalKimya Bilimleriİngilizce
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In 1890, chemists had to work hard to find out what the structures of their molecules were, given they had no access to the plethora of modern techniques we are used to in 2010. For example, how could they be sure what the structure of naphthalene was? Well, two such chemists, William Henry Armstrong (1847-1937) and his student William Palmer Wynne (1861-1950;

Interesting ChemistryAnimationCatalysisFree EnergyFree Energy BarrierKimya Bilimleriİngilizce
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Reactions in cavities can adopt quite different characteristics from those in solvents. Thus first example of the catalysis of the Diels-Alder reaction inside an organic scaffold was reported by Endo, Koike, Sawaki, Hayashida, Masuda, and Aoyama[cite]10.1021/ja964198s[/cite], where the reaction shown below is speeded up very greatly in the presence of a crystalline lattice of the anthracene derivative shown below. A Diels-Alder reaction.