Leaving Groups and Nucleophiles

At this point, the only leaving group you are really familiar with is alkyl halides. It turns out there are 2 more you should definitely know about. 

Leaving Groups

1. Alkyl Halides

We’ve been dealing with these the whole lesson, formula –RX. You should be cool with these

2. Sulfonate Esters

These are molecules with the general structure –OSO2R or –SO3R. These are the ultimate leaving groups of organic chemistry. They might look a little weird, but in the end of the day, remember they just leave. NBD. 

3. Water

Also an awesome leaving group, formed after alcohol is protonated with a strong acid.

Nucleophiles and Basicity

Concept: Understanding the difference between basicity and nucleophilicity.  


Recall that a Nucleophile is an electron pair donor (Lewis Base), and a Base is a proton acceptor (Bronsted-Lowry Base).

While the terms nucleophile and base often mean the same thing, there are some exceptions where basicity and nucleophilicity do not mirror each other.

Relative Strength Rules:

  1. A negative charge will always be a stronger nucleophile than its neutral counterpart.
  2. The bulkier the base, the more basic and less nucleophilic it is.
  3. Basicity and nucleophilicity have opposite size trends in polar protic solvents.