In fact successive addition tends to be the normal

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Unformatted text preview: uccessive addition tends to be the normal mode of reactivity for alkynes, as addition to the alkene is generally faster than the initial alkyne addition. H CH3CH2C C Br H Br + H–Br H CH3CH2C C H Br H a geminal dibromide a vinyl bromide (an alkene) One reason why the subsequent reaction is faster is because of the special stability of the carbocation intermediate that results when an electrophile adds to a vinyl bromide. The lone pairs on the bromo group can donate to the electron deficient carbocation. Although this places a positive charge on the electronegative bromo group, all atoms have an octet of electrons making this a very important resonance contributor. H CH3CH2C C H Br H n → a π-type resonance interaction H CH3CH2C C H Br H the most important resonance contributor (each atom has an octet of electrons)...
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