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Regioselectivity can also be applied to specific reactions such as addition to pi ligands. Selectivity also occurs in carbene insertions, for example in the Baeyer-Villiger reaction. In this reaction, an oxygen is regioselectively inserted near an adjacent carbonyl group.
In this example the ring system can be thought of as analogous to 1,3-butadiene. Following the Green–Davies–Mingos rules, since butadiene is an open π-ligand of even hapticity, nucleophilic attack will occur at one of the terminal positions of the π-system.
For terminal olefins (or acetylenes), the regioselectivity of the process can be described as Markovnikov (addition of X at the substituted end) or anti-Markovnikov (addition of X at the unsubstituted end). Catalysts are frequently employed to control the chemo-, regio-, and stereoselectivity of hydrofunctionalization reactions.
Shown below is an example of regioselectivity and stereospecificity of the oxymercuration reaction with substituted cyclohexenes. A bulky group like t-butyl locks the ring in a chair conformation and prevents ring flips.
The dominant electronic interaction is the combination between the largest HOMO and the largest LUMO. Therefore, regioselectivity is governed by the atoms that bear the largest orbital HOMO and LUMO coefficients. [29] [30] For example, consider the cycloaddition of diazomethane to three dipolarophiles: methyl acrylate, styrene or methyl ...
A famous example is the Luche Reduction, where an oxophilic metal makes the carbonyl of a conjugated ketone more reactive and directs the reducing agent. [6] On the other hand, copper organometallics have high affinity with carbon-carbon multiple bonds and are used for conjugate addition of nucleophiles into a conjugated ketone.
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One example of this is a study conducted by D. Fattori looking at the regioselectivity of the Demjanov rearrangement in one-carbon enlargements of naked sugars. It showed that when an exo methylamine underwent Demjanov nitrous acid deamination, ring enlargement was not produced.