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A stereospecific mechanism specifies the stereochemical outcome of a given reactant, whereas a stereoselective reaction selects products from those made available by the same, non-specific mechanism acting on a given reactant. Given a single, stereoisomerically pure starting material, a stereospecific mechanism will give 100% of a particular ...
In organic chemistry, regioselectivity is the preference of chemical bonding or breaking in one direction over all other possible directions. [1] [2] It can often apply to which of many possible positions a reagent will affect, such as which proton a strong base will abstract from an organic molecule, or where on a substituted benzene ring a further substituent will be added.
An example of modest stereoselectivity is the dehydrohalogenation of 2-iodobutane which yields 60% trans-2-butene and 20% cis-2-butene. [5] Since alkene geometric isomers are also classified as diastereomers, this reaction would also be called diastereoselective.
Regiospecific hydroboration with borane Hydroboration-oxidation of (E)-prop-1-en-1-ylbenzene Hydroboration-oxidation of 1-methyl-cyclohex-1-ene. The net reaction is hydration. Because the addition of H-B to olefins is stereospecific, this oxidation reaction will be diastereoselective when the alkene is trisubstituted. [10]
The reaction thus provides a more stereospecific and complementary regiochemical alternative to other hydration reactions such as acid-catalyzed addition and the oxymercuration–reduction process. The reaction was first reported by Herbert C. Brown in the late 1950s [2] and it was recognized in his receiving the Nobel Prize in Chemistry in 1979.
Stereospecific: Can be syn or anti addition, depending on situation. When alkenes undergo hydrobromination, the alkyl bromides are formed Markovnikov. Alkyne oxymercuration-demercuration: In this reaction, HgSO 4 reacts with an alkyne in a Markovnikov regioselective manner to form an enol that is tautomerized into a ketone. This process ...
Despite the fact that the vast majority of Diels–Alder reactions exhibit stereospecific, syn addition of the two components, a diradical intermediate has been postulated [7] (and supported with computational evidence) on the grounds that the observed stereospecificity does not rule out a two-step addition involving an intermediate that ...
The Simmons–Smith reaction is an organic cheletropic reaction involving an organozinc carbenoid that reacts with an alkene (or alkyne) to form a cyclopropane. [1] [2] [3] It is named after Howard Ensign Simmons, Jr. and Ronald D. Smith.