Rules of the Day 320N

1. Mammalian vision is the result of a photon being absorbed by a molecule called 11-cis-retinal, converting the cis C=C to a trans C=C, resulting a signal being sent to the brain. 11-Cis-retinal, is reversibly held in the protein pocket of the opsin protein by a C=N (Schiff Base) so it can be recycled after absorbing a photon. 11-Cis-retinal is a terpene, meaning it comes from plants (!) explaining why vitamin A (the alcohol form of retinal) is an ESSENTIAL vitamin in our diet (carrots, etc.).

2. Hydrazine (H2N-NH2) or hydroxylamine (H2N-OH) react with aldehydes and ketones just like amines to create hydrazides and oximes, respectively, species with a C=N.

3. The Clemmensen reduction uses Zn(Hg) and HCl to convert the carbonyl groups of ketones and aldehydes into CH2 groups. The mechanism of this reaction is complex and will not be covered in this class. This reaction cannot be used if there are acid sensitive groups such as tertiary alcohols (they can lose H2O to give an alkene) or acetals present.

4. The Wolff-Kishner reduction, the one with the "scary" mechanism, uses NH2-NH2 and HO- to convert the carbonyl groups of ketones and aldehydes into CH2 groups. This reaction can be used when acid sensitive groups are present. The mechanism involves hydrazone formation, two detprotonations by HO-, loss of N2 and two protonations of the carbon atom that used to be the carbonyl carbon atom. Remember, the "Wolff " bites little red riding hood's head (aka carbonyl O atom) clean off!!

5. Oxidation-reduction reactions of carbonyl reactions are useful for putting together multiple reactions in sequence during organic synthesis.

6. Imines can be reduced as they are made to give amines if H2/Pd or NaCNBH3 is added to the reaction.

7. Keto-enol equilibration is catalyzed by acid or base. Recall that catalysis does not change the position of equilibrium, but just accelerates the rate at which equilibrium is achieved. The keto form is almost always favored (C=O stronger bond than C=C)! In acid, the mechanism involves protonation of the carbonyl oxygen atom, followed by loss of a proton by the alpha-carbon atom.

8. The alpha-hydrogens of aldehydes and ketones are relatively acidic with a pKa around 20. Deprotonated aldehydes or ketones are resonance stabilized and are called enolates. The resonance stabilization of the enolate explains the relative acidity of aldehydes/ketones.

9. Base-catalyzed keto-enol equilibrium occurs via an enolate intermediate.

4. The enol form of a carbonyl reacts like an alkene, so even though it is only present in small amounts, some reactions characteristic of alkenes can be made to occur with aldehydes and ketones such as halogenation with X2 at the alpha position.

Homework:

Read: Sections 17.1-17.4 in the ebook textbook. This text is part of the Longhorn Textbook access program.

Take the Daily Quiz 7 before 10 PM tomorrow. Click here to access the quiz. These quizzes are designed to review the important material from today's lecture. Together, they will count as 3% of your final grade.

Continue working on the Gradescope Homework Problem Set 3, due at 10 PM on Wednesday, February 5. Click here to access the Homework Problem Set 3.

There is also an Aktiv Learning Homework Problem Set 3 as well (there was no Aktiv Learning homework Problem Set 1) If you already have an Aktiv Learning account, click here to get the Aktiv Homework Problem set 3 (there was no Aktiv Homework Problem set 1)

Homeworks will be worth 10% of your final grade (20% from the Aktiv Learning and 80% from the Gradescope portions of the homework).