Interpretation:
Out of the two given ketones, A and B, which ketone will undergo bromination faster under acidic conditions is to be determined.
Concept introduction:
Alpha halogenation is the halogenation at the alpha carbon atom of an
Under the acidic conditions, the first step is the protonation of carbonyl oxygen. In the second step, the acetate ions serve as a base and abstract an alpha proton from ketone; this yields an enol form. In the enol form, the alpha carbon is electron rich due to the small contribution by the resonance structure in which a negative charge and a lone pair of electrons are located on the alpha carbon. Alpha halogenation occurs only once as the electron withdrawing effect of bromine destabilizes the positive charge if the carbonyl oxygen gets protonated further. This reduces the chances of the second halogenation.
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ORGANIC CHEMISTRY E-BOOK W/SMARTWORK5
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- Organic Chemistry: A Guided InquiryChemistryISBN:9780618974122Author:Andrei StraumanisPublisher:Cengage Learning