Rules of the Day
2-22-2024
Click here for a copy of the lectures notes I wrote in class
Click here for a copy of the handouts I used in class today
Featured Golden Rule of Chemistry: 10. A reaction mechanism describes the sequence of steps occurring during a reaction.10. A reaction mechanism describes the sequence of steps occurring during a reaction.
When learning mechanisms, the key to "catching the wave" is to always ask yourself WHY each step happens the way it does. When you start understanding the answers to that question at each step, the whole thing will make sense.
You should keep a few things in mind when writing these complex mechanisms to make sure you are not making any mistakes: 1) Identify the bonds to be made and broken 2) Avoid "mixed media errores". In acid all intermediates are positively-charged/neutral, in base all intermediates are negatively-charged/neutral, in neutral solution the intermediates can be positvely-charged or negatively-charged 3) Proton transfers are fast 4) Evaluate properties of intermediates to predict next step.
2. Esters require acid catalysis or base promotion to hydrolyze. The acid catalyzed ester hydrolysis mechanism is the functional reverse of the Fischer esterification mechanism, illustrating the concept of microscopic reversibility.
3. Microscopic reversibility predicts that you encounter the same intermediates in either direction of a reversible reaction. You will also see the complement mechanistic elements (make a bond vs. break a bond and add a proton vs. take a proton away) at each step in either direction. Is it really true? Can mechanisms really make that much sense? Mind officially blown.
4. Base promoted ester hydrolysis is just Mechanism B followed by an acid base reaction.
5. Heating in aqueous acid hydrolyzes amides in a mechanism analogous to the acid catalyzed ester hydrolysis reaction except for amides the reaction is only promoted by acid, not catalyzed by it, because the last step involves transfer of a proton to the amine group that departed.
Homework:
Read: Sections 18.8-18.11 in the ebook textbook. This text is part of the Longhorn Textbook access program.
There is no daily quiz due tomorrow! Go have a mechanism party instead!!! Wo hooo!!
