How To Stabilize Negative Charge

by Kiley Lynch

Maybe you’ve heard of the Pareto Principle, otherwise known as the 80/20 rule. 20% of the work gets you 80% of the results. Wouldn’t it be nice to know a few of the principles that fall into that 20% for organic chemistry?
Well here’s a big one. This is one of the most important concepts to grasp in all of organic chemistry. Understand factors which stabilize negative charge.

Here are 5 key factors:

  1. Electronegativity – across a row to the right, negative charge is stabilized , because it is drawn closer to the positively charged nucleus.
  2. Polarizability  – down a column, negative charge is stabilized, because the negative charge is distributed over a greater volume
  3. Resonance stabilizes negative charge, since it can be distributed over a larger area.
  4. Electron withdrawing groups also stabilize negative charge, for reasons similar to electronegativity.
  5. Orbitals: – the more s character there is,  the more negative charge is stabilized. Stabilization is best for  sp > sp2 > sp3, since the negative charge will be held more tightly to the nucleus.

OK, so why is this important?

  1. Understanding acidity: The strength of an acid is related to the stability of its conjugate base, and many conjugate bases bear a negative charge. So understanding these factors helps to determine which is a more stable (or unstable) base, and therefore what is a stronger (or weaker) acid.
  2. Understanding the stability of resonance forms: if you have to put a negative charge on a resonance form, these guidelines will help you decide on the best place to put it!
  3. Understanding reactivity. This isn’t the place to discuss it yet, but coming up, we’re going to talk about two topics you’re familiar with already, but have weird unfamiliar names (nucleophilicity and leaving group ability) and this will be super important.

Tomorrow: how to avoid some common mistakes students make with resonance.

Thanks for reading! James