Today, we're going to add the reactions of alkynes to our reaction map, which will bring to a close all the major reactions we've discussed so far in a typical first semester course. Like alkenes, the main pathway found in the reactions of alkynes is "addition" - that is, breaking the C-C π bond … [Read more...]
Alkynes Are A Blank Canvas
Now that we've gone through all the major reactions of alkynes, we can take a step back and look at the big picture. There are lots of reactions of alkynes. So what? you might ask. In this post I will try to convince you that alkynes are really useful building blocks for synthesizing a large variety … [Read more...]
Alkynes Via Elimination Reactions
We've gone through elimination reactions before - treatment of alkyl halides with base gives alkenes. Some time ago we discussed elimination reactions here. Elimination reactions follow the general pattern below, where two adjacent bonds to carbon are broken - usually C-H and C-X, where X is a … [Read more...]
Alkyne Addition Reactions – The “Concerted” Pathway
How does the chemistry of alkynes compare to alkenes? As we've seen in some previous posts, there are some significant differences, but a lot of the chemistry "rhymes", if you will. In the series on alkenes we broke down most of the reactions into three major categories according to their mechanisms … [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...]
Alkyne Reaction Patterns – The Carbocation Pathway
In the previous three posts on alkynes we've introduced some new reactions that are specific to alkynes (versus alkenes): deprotonation (and subsequent substitution), partial reduction to alkenes, and formation of aldehydes and ketones through net "hydration". With all the focus on the … [Read more...]
Hydroboration and Oxymercuration of Alkynes
Alkyne chemistry bears many resemblances to alkene chemistry, but in these first few posts on the subject, the purpose is to illustrate how one seemingly minor change - an extra π bond - can lead to significant differences in chemical behavior. Previously, we saw that the sp hybridization of alkynes … [Read more...]
Partial Reduction of Alkynes To Obtain Cis or Trans Alkenes
Alkynes bear many similarities to alkenes, but as we have already seen, their chemistry can differ in subtle and interesting ways. Today's post is another case in point. Using a normal catalyst, hydrogenation of alkynes gives alkanes The reduction of alkenes by hydrogen in the presence of a metal … [Read more...]