As we discussed in the last post on radicals, bromine radicals are considerably more selective than chlorine radicals in the halogenation of alkanes. For example, a hydrocarbon exposed to Br2 in the presence of heat or light (for initiation) can selectively be brominated at the tertiary C–H bond, … [Read more...]
Selectivity in Free Radical Reactions: Bromine vs. Chlorine
In last blog post on radicals we saw this data that compares the chlorination of propane vs. the bromination of propane: Bromination: We also saw that when you take statistics into account, the selectivity of these reactions are different. For chlorination, the reaction is selective for … [Read more...]
Alkyne Addition Reactions: The 3-Membered Ring Pathway
Last time we discussed the similarities (and differences) between the carbocation pathway for alkenes and alkynes. In this post, we'll do the same for the "3-membered ring pathway". If you'll recall from the series of posts on alkenes, alkenes react with certain electrophiles (such as halogens, … [Read more...]
Bromination of Alkenes: The Mechanism
How does bromination of alkenes work? In the previous post we showed how the mechanism for bromination of alkenes can't possibly go through a carbocation intermediate. Why not? We have at least 3 good reasons: It's stereoselective. The two atoms that form new bonds to carbon add to … [Read more...]