Chemical Forums

Please login or register.

Login with username, password and session length

Sponsored links

Pages: [1]   Go Down

Author Topic: Why does this have a higher pka?  (Read 345 times)

0 Members and 1 Guest are viewing this topic.

Starksays

  • Regular Member
  • ***
  • Mole Snacks: +0/-0
  • Offline Offline
  • Posts: 10
Why does this have a higher pka?
« on: March 05, 2013, 03:30:48 AM »

Why would something like 3-bromobutyric acid have a higher pka than 2-bromobutyric acid? Does it have anything to do with an electronegative bromine closer to the carboxylic acid group? What exact effect is it having?
Logged

Sophia7X

  • Full Member
  • ****
  • Mole Snacks: +32/-4
  • Offline Offline
  • Gender: Female
  • Posts: 249
  • I, a universe of atoms, an atom in the universe.
Re: Why does this have a higher pka?
« Reply #1 on: March 05, 2013, 09:27:38 AM »

When there is an electronegative group close to the acidic hydrogen, an effect called "induction" happens.

If you draw the conjugate bases of the 2- and 3-bromobutyric acids, the oxygen from both structures will have a negative charge. So the difference arises from the location of the bromine, one is closer and the another is farther away.

Bromine will withdraw electron density away from the negatively charged Oxygen by an inductive effect. This stabilizes the negative charge by spreading it out, as opposed to keeping it concentrated to the oxygen.

If the conjugate base is more stable, it is weaker so its acid must be stronger.
Logged
Entropy happens.

Pages: [1]   Go Up
 

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 0.049 seconds with 23 queries.