Nasiri CHE118B Final Study Guide Spring 2019 || S. Ly [email protected]CH 17: Aldehydes and Ketones → NAMING ALDEHYDES ● Alkanal ○ Aldehyde function is always carbon #1 ! ● In cyclic form: cycloalkanecarbaldehyde → NAMING KETONES ● Alkanone ● In cyclic form: cycloalkanone ● Priority: aldehydes > ketones > alcohols ○ As a substituent: oxo- → SYNTHESIS OF ALDEHYDES AND KETONES Recall previous reactions… New reactions: ● Oxidation of allylic alcohol : only the allylic alcohol gets oxidized.
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CH 17: Aldehydes and Ketones · 2019. 9. 11. · → O XIDATION TESTS FOR ALDEHYDES Tollen’s reagent = [Ag(NH3)2]OH Forms a silver mirror precipitate Reacts only with aldehydes,
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Nasiri CHE118B Final Study Guide Spring 2019 || S. Ly [email protected]
CH 17: Aldehydes and Ketones → NAMING ALDEHYDES
● Alkanal ○ Aldehyde function is always carbon #1 !
Nasiri CHE118B Final Study Guide Spring 2019 || S. Ly [email protected]
● Unlike hemiacetals and geminal diols, acetals can be isolated!
** Fill in mechanism below (all steps should be reversible)
● Intramolecular acetal formation is possible.
● Recall 5 and 6 membered rings are the most stable. ● If you have two carbonyls on one molecule, acetals are a good way to protect one of those groups
Nasiri CHE118B Final Study Guide Spring 2019 || S. Ly [email protected]
→ ALPHA HALOGENATION ● In acidic medium -> monohalogenation
** Fill in the mechanism below:
● In basic medium -> polyhalogenation ○ All alpha H’s get replaced by the halogen
● Iodoform test: ○ Used to test for presence of methyl ketones. Positive test yields a yellow precipitate. ○ Can use other halogens besides iodine too (except F)
** Fill in the mechanism below: → ALPHA ALKYLATION
● The enolate ion can be used to do an alkylation reaction. ○ Problems:
■ Must be a methyl halide or a primary haloalkane; otherwise E2 reaction may occur
Nasiri CHE118B Final Study Guide Spring 2019 || S. Ly [email protected]
■ With aldehydes, there is a competing reaction: aldol condensation ■ With ketones, polyalkylation is possible. The first alkylation product may form
another enolate and do another alkylation reaction
● To avoid these problems, enamines can be used as a type of protecting group, since they have
enolate ion characteristic. ○ Halide can be methyl, primary, or secondary ○ No polyalkylation
→ ALDOL CONDENSATION
● Yield is lower for ketones than aldehydes ● Requires at least two alpha hydrogens ● ALWAYS count your carbons to check your answer. (i.e. adding an ald with 3 C + ald with 4 C ->
product should have 7 C) ** Fill in the mechanism below:
Nasiri CHE118B Final Study Guide Spring 2019 || S. Ly [email protected]
● Intramolecular aldol condensation is possible. Recall, 5 and 6 membered rings are the most favorable.
● When a reaction has two different aldehydes, mixed condensation occurs.
● To prevent this from happening, make sure one of the reagents does not have 2 alpha Hs. ● Using a ketone can also be effective because ketones are less reactive than aldehydes.
→ CONJUGATED ALPHA-BETA UNSATURATED ALDEHYDES AND KETONES
● Aldol condensation leads to an important product: conjugated α-β-unsaturated aldehydes/ketones
● Can be synthesized in other ways too:
● Nucleophilic addition goes through two routes: 1,2 and 1,4 addition
1,2 ADDITION: ● Involves only one double bond and not both ● Favored by RMgX, RLi, NaBH4, LiAlH4, X2
Nasiri CHE118B Final Study Guide Spring 2019 || S. Ly [email protected]
* KEY Refer to lecture notes for mechanisms. If you need help or have found any mistakes, e-mail me or come to my office hours (MON: 9 - 10:45 AM CHEM159 // TUES: 4:30 - 6:00 PM CHEM163K)