Formation of Bromohydrins from alkenes using water and Br2
Description: Alkenes treated with bromine (Br2) or N-bromosuccinimide (NBS) in the presence of water will form bromohydrins.
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Real-Life Examples:
Org. Synth. 1979, 59, 16
DOI Link: 10.15227/orgsyn.059.0016
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Org. Synth. 1977, 56, 112
DOI Link: 10.15227/orgsyn.056.0112
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Thanks so much James, really fabulous website..
in second example, is there enantiomers?
Yes, the second example would have a mixture of enantiomers since there is a chiral center at C-2
in the mechanism, the lone pair attacks back to the double bond (right?) and if so, does it matter which side it attacks?
Yes it does. Thanks for bringing this up. Both bonds to the Br will be on the same face (formation of the bromonium ion is “syn”).
Is it possible to produce a halogenoalkane as a side product in this reaction, that is, Br- attacks the bromonium ion in the sec step?
yes, but keep in mind the concentration of solvent is significantly higher than the concentration of the counter-ion, so it will be very small [concentration of H2O in 1L of water is 55 M!] At very high concentrations it might become more significant.