week five of Summer Session 2 2019
CLASS LOGISTICS
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chapter 17: Aldehydes and ketones
nomenclature
synthEsis of ketones and aldehydes:
(Six reactions- one new reaction & five review)
Reaction #1: MnO2 w/ allylic OH (NEW REACTION)
Reaction #2: PCC & Jones on OH
Reaction #3: Ozonolysis of alkenes
Reaction #4/5: Hydration of alkynes
Reaction #6: Friedel Crafts Acylation
Reaction #1: formation of hydrates (geminal diols)
Unfortunately, all of the videos (Khan Academy, The Organic Chemistry Tutor, etc) that I saw were flawed or different than what Dr. Nasiri taught when it came to formation of hydrates and hemiacetals/hemiketals. Mainly, they did not show the reactions and mechanisms in either acidic or basic medium.
Exceptions to the above reaction rule that states that the equilibrium favors the aldehyde or ketone:
-Formaldehyde
-Trifluoroacetaldehyde
-Cyclopropanone
-Formaldehyde
-Trifluoroacetaldehyde
-Cyclopropanone
REACTION #2: formation of hemiacetals and hemiketals
The above exceptions for hydrate formation equilibrium also apply to the formation of hemiacetals and hemiketals.
For this reaction, we add a fourth exception, which is shown in the lower half of the image above: formation of 5 or 6-membered cyclic hemiacetals
For this reaction, we add a fourth exception, which is shown in the lower half of the image above: formation of 5 or 6-membered cyclic hemiacetals
reACTION #3: formation of acetals and use as protecting groups
Therefore, if you have a ketone or aldehyde and 2 equivalents of your alcohol in acidic conditions, you will form an acetal.
This reaction is reversible. On exams, to turn an acetal back to a ketone or aldehyde, add H3O+ and heat. More water will push the reverse reaction towards the ketone/aldehyde.
This reaction is reversible. On exams, to turn an acetal back to a ketone or aldehyde, add H3O+ and heat. More water will push the reverse reaction towards the ketone/aldehyde.
REACTION #4: Formation of thioacetals and use as protecting groups
A thiol is an organosulfur compound with the structure: R-SH
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-In the first reaction in the video, that forms the thioacetal, you can replace BF3 with ZnCl2.
-Just like acetal formation, thioacetal formation requires 2 equivalents of your thiol RSH. Questions at the end of the video: A- Turns acetal back to ketone B- Replaces carbonyl with 2 thiol groups C- Removes both thiol groups End product: cyclobutane |
Thioacetal-hydrogenolysis: (new reaction)
REACTION #5: Addition of Nh2 and its derivatives to aldehydes and ketones
Primary amines + carbonyl = Imine
Secondary amines + carbonyl = Enamine
Secondary amines + carbonyl = Enamine
REACTION #6: Wolff kischner reduction
Wolff-Kischner vs. Clemmensen Reduction- Zn(Hg), HCl
-Gives the same products, but Clemmensen uses HCl (Acidic) vs. Kischner's NaOH (Base)
-Gives the same products, but Clemmensen uses HCl (Acidic) vs. Kischner's NaOH (Base)
REACTION #7: formation and reactions of cyanohydrins
Writing "NaCN, HCl" is the same as writing "HCN," because NaCN reacts with HCl to form HCN.
Mechanism of the formation of Cyanohydrin:
REACTION #8: the wittig reaction
REACTION #9: Baeyer-villiger oxidation
REACTIOn #10: Testing for aldehydes
We can use two reactions to test for the presence of an aldehyde. The color change indicates the aldehyde's presence.
Mnemonic: Tollen's test has a "toll" in the name. You can pay for your toll fee with silver (Ag).
Mnemonic: Tollen's test has a "toll" in the name. You can pay for your toll fee with silver (Ag).