Rules of the Day 320N

1. You are responsible for learning the nomenclature of carboxyic acids (Section 17.2) and the carboxylic acid derivatives of esters and amides only (Section 18.1C and 18.1D).

2. Amides are amazing functional groups. The lone pair on nitrogen is shared in a delocalized pi system involving three atoms, the N, C, and O of the amide (third contributing structure). The amide nitrogen atom is therefore sp2 hybridized, not sp3 as you might expect. This also means there is partial double bond character (restriction of bond rotation) of the C-N bond and the carbonyl O atom has a lot of electron density, making it better at hydrogen bonding. These properties are responsible for life as we know it because they provide the structural elements necessary to form stable 3-dimensional objects from long 1-dimensional chains of amino acids.. See the picture of the day for more details.

3. Carboxylic acid derivatives all have leaving groups of various abilities. The more stable the anion, the better then leaving group, so relative leaving group abiilty is correlated with relative pKa of leaving group conjugate acid. The better the leaving group, the more reactive the carboxylic acid derivative.

4. Carboxylic acid derivatives react though variations of Mechanism B because they all have leaving groups of various abilities attached.

5. Acid chlorides and anhydrides are very reactive, esters are moderately reactive, and amides are unreactive.

6. You can make any of the less reactive carboxylic acid derivatives from any of the more reactive ones with the appropriate nucleophiles. You can make acid chlorides from carboxylic acids. You can make carboxylic acids from the hydrolysis of any of the carboxylic acid derivatives. Therefore, you can convert any carboxylic acid derivative into any of the other ones.

7. All of the carboxylic acid derivative mechanisms involve the four mechanistic elements: Make a bond, Break a bond, Add a proton, Take a proton away.

8. 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.

9. 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.

10. Anhydrides react with water to produce two molecules of carboxylic acid and this process is catalyzed by acid.

11. 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.

12. 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.

Homework:

Read: Sections 18.5-18.7 in the ebook textbook. This text is part of the Longhorn Textbook access program.

Take the Daily Quiz 9 before 10 PM tomorrow. Click here to access the quiz.

Start working on the Homework Problem Set 5, due at 10 PM on Monday, February 26. Click here to access the Homework Problem Set 5. Remember to do both the Aktiv learning and Gradescope portions of the homework! We will be grading the Gradescope homework for completion only, not accuracy. This is a guaranteed 100% on a homework if you turn it in complete! I promise that if you spend the time to work through all these mechanisms even before we talk about them in class you will be a mechanism wizard and will do great on these for all of the remaining exams! No joke, this is your chance, you can do this!