Bromonium ions, cyclic detection

From alkylacetylenes trans dibromide is formed in large or quantitative yields and no detectable amounts of cis or solvent-incorporated diadducts were observed. The indications are that in this case the electrophilic addition occurs via a cyclic bromonium ion (47) and that this is probably more stable as an intermediate than the linear alkyl vinyl oation. From 47 only trans addition is expected to occur. 

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