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Maybe a month ago you might remember me writing that the key theme of Org 1 is stereochemistry? Well, here we go again! Except now we’re talking about addition reactions.

In addition to regiochemistry (“Markovnikoff / anti-Markovnikoff”) of alkene addition reactions, the stereochemistry is important too.

This picture will hopefully show what I mean.

Since we’re always forming two new bonds to carbon, the relative orientation of these bonds is important.

  • In some addition reactions, these bonds always form on the same side of the alkene. We call this arrangement “syn”. 
  • In other addition reactions these bonds always form on opposite sides of the alkene. We call this arrangement “anti”.
  • Finally, there are also reactions where these bonds form with no consistent preference for arrangement on the same or opposite side. We call this arrangement “random“.

Initially, keeping track of the stereochemistry of alkene additions might seem like a lot of work. And to some extent, it is. However, I’m going to show you how you can simplify your study work considerably by considering 3 key patterns in addition to alkenes. 

Tomorrow, we’ll look at the first big pattern. 

Thanks for reading! James