Midterm 3 Review Flashcards
Why does the electrophile add to the alpha carbon of the keto instead of the oxygen? (The counter ion is Na+)
The counter ion Na+ is more tightly associated with the oxygen than the alpha carbon thus block the approach of the electrophile
Acetaldehyde ->
Reagent: NaOH
H-carbonyl-deprotonated CH2 + H2O
Aldol Condensation Reaction
Which side predominates in Aldol Condensation Reaction?
Reactants
A) H-carbonyl-deprotonated CH2
B) Acetaldehyde
Which is nucleophilic and which is electrophilic?
A is nucleophilic, B is electrophilic
H-carbonyl-deprotonated CH2 + Acetaldehyde ->
Attack of the Nu: arrow from carbon lone pair to electrophile’s carbonyl carbon, whose double bond goes up to oxygen
Product: H-carbonyl-CH2-C bound to OH, CH3, and H (B-hydroxyaldehyde)
Racemic about OH
In B-hydroxyaldehyde which carbon is alpha and which is beta?
CH2 = alpha, C bound to OH = beta
B-hydroxyaldehyde ->
Reagent: H3O+
OH is a leaving group, double bond forms between alpha and beta carbons
Product: H-carbonyl-CH=CH-CH3 (a-B-unsaturated carbonyl compound)
Both E & Z alkene can be formed, stable
Dehydration
A) Acetaldehyde
B) H-carbonyl-Ph
Which one is more electrophilic and why?
B because Ph EWG makes B’s carbonyl carbon more reactive than A’s
Acetaldehyde + LDA <->
What is the product? Which side predominates?
H-carbonyl-deprotonated CH2
Almost 100% conversion
Products predominate
What molecule will undergo Intramolecular Aldol Condensation? What is the product?
Reagents: 1) NaOH, 2) H3O+
Number the deprotonated carbon as 1, if the last carbon (5 or 6) is an aldehyde you can cyclize! Double bond O from aldehyde on 6th carbon becomes OH. Carbons 1 and 6 are racemic.
Dehydration: OH goes away, double bond forms between 1 and 6 (a-B unsaturated aldehyde)
How many eq LDA are needed to cyclize?
1
How many eq LDA are needed for Aldol Condensation Reaction?
0.5
Retrosynthesize a 6-membered ring with carbonyl and double bond between a and B carbons
It must have come from an Intramolecular Aldol Condensation: break the bonds between a and B and put an aldehyde on B
How many eq LDA are needed for Cross-Aldol Condensation?
1
Retrosynthesize a ketone with Ph attached to one side and terminal alkene attached to other side
Ph attached to ketone + formaldehyde
Ethyl ester ->
Reagents: 1) NaOEt, EtOH
2) H3O+
Double bond O side x2 with alpha carbon on starting material bound to carbonyl carbon on substituent (B-ketoester)
Claisen Condensation
Why must you match the tail of the ester to the tail of the base in Claisen Condensation?
To prevent transesterification
How many eq LDA are needed for Claisen Condensation?
0.5
A) ethyl ester with alpha hydrogens
B) ethyl ester with no alpha hydrogens ->
Reagents: 1) NaOEt, EtOH
2) H3O+
Entirety of A with its alpha carbon bound to B’s carbonyl carbon (B-ketoester), ester O + tail go away
Cross Claisen Condensation
How many eq LDA are needed for Cross Claisen Condensation?
1
What molecule will undergo Dieckmann Condensation (Intramolecular Claisen Condensation)? What is the product?
Reagents: 1) NaOEt, EtOH
2) H3O+
Ester on both sides. Number the alpha carbon as 1, if the last carbon (5 or 6) is a carbonyl you can cyclize! 1 and 6 form a bond. 6’s O + tail is LG. Carbons 1 is racemic. (B-ketoester)
How many eq LDA are needed for Dieckmann Condensation?
1
Retrosynthesize B-ketoester
Using ester carbonyl to determine a and B carbon, break bond between alpha and beta, add OEt to beta carbon
Carboxylic acids ->
Reagents: excess EtOH, cat H2SO4
EtO substitutes OH on carboxylic acids
Enolate anion ->
Reagent: propyl-Br
Double bond goes away, propyl added to terminal carbon
Alpha-alkylation
Enamine ->
Reagents: 1) propyl-Br, acid chloride, or CH3Br
2) H3O+
Carbonyl that the enamine came from (carbonyl, 2° amine, pH = 4) adds substituent and it’s racemic if tertiary
a-alkylation
In an a-B-unsaturated aldehyde, which carbon is electrophilic? When it resonates to an enolate anion, which carbon is electrophilic?
First the carbonyl carbon, then the terminal/least substituted carbon (not involved in the double bond)
a-B-unsaturated aldehyde ->
Reagents: 1) (CH3)2CuLi, 2) H3O+
Double bond goes away, CH3 added to beta carbon which is racemic if tertiary
Michael Addition
H3C-carbonyl-ethyl ester (2 ketones) (Acetoacetic Ester/B-ketoester) ->
Reagents: 1) NaOEt, EtOH
2) SN2 CH3-I
3) NaOH, H2O
4) H3O+
5) Heat
1) deprotonate the alpha carbon
2) CH3 adds to deprotonated site and is racemic
3-5) ethyl ester goes away
Ketone-ethyl ester ->
Reagents: 1) NaOH, H2O
2) H3O+
Ester tail(s) substituted by H (forming carboxylic acid)
Malonic Ester ->
Reagents: 1) NaOEt, 2) Epoxide, 3) H3O+, 4) H3O+, 5) Heat, 6) H3O+
1) Deprotonate alpha carbon
2) 2 carbons and O- added at deprotonated site
3) O- becomes OH
4) Hydrolyze ester: ester tail(s) substituted by H (forming carboxylic acid)
5) One carboxylic acid goes away
6) Cyclize forming an ester (H goes away on both OHs)
Malonic Ester ->
Reagents: 1) NaOEt, EtOH
2) Ketone on cyclohexane with a-B alkene
3) NaOH, H2O
4) H3O+
5) Heat
1) Deprotonate
2) Form a bond between B carbon and deprotonated site, double bond on substituent goes away
3-4) Ester tail(s) substituted by H
5) One carboxylic acid goes away, B carbon is racemic
1) Ketone on cyclohexane, another ketone at B position
2) Ketone on cyclohexane with a-B alkene
Which is the Michael donor? Michael Acceptor? Electrophile? Nucleophile?
1, 2, 2, 1
1) Ketone on cyclohexane, another ketone at B position
2) Ketone on cyclohexane with a-B alkene
Reagents: NaOH, H2O
1 deprotonates alpha carbon, forms a bond with 2’s B carbon whose double bond moves one toward its O & double bond O becomes O-, double bond within cyclohexane goes away & B carbon is racemic & O- becomes double bond O again
Retrosynthesize an enamine
NH bound to its substituents + ketone without C=C double bond
Ketone with a-B alkene ->
Reagents: 1) Enamine (double bond between “carbonyl” carbon and alpha carbon and a gamma carbon), 2) H3O+
Retrosynthesize the enamine to the carbonyl compound (Donor) and bond the Donor’s alpha carbon to the Michael Acceptor’s beta carbon, acceptor’s C=C double bond goes away, donor’s alpha carbon is racemic (because tertiary)
Michael Acceptor
Always has a carbonyl and a-B alkene
A) Donor with deprotonated alpha carbon (between two carbonyls)
B) acceptor
Reagents: 1) NaOEt, EtOH
2) H3O+ (workup)
Donor’s alpha carbon bonds with acceptor’s beta carbon, acceptor’s C=C double bond goes away, donor’s alpha and acceptor’s beta carbons are racemic (tertiary)
A) acceptor
B) H2N-Et (donor)
What is the product?
1° amine loses one H, and N forms a bond with acceptor’s beta carbon whose C=C double bond goes away
A) carbonyl compound with C [triple bond] N (nitrile) at the beta position
B) acceptor
Reagents: 1) NaOEt, 2) H3O+ (workup)
The donor A’s alpha carbon forms a bond with acceptor’s beta carbon, acceptor’s C=C double bond goes away, donor’s alpha carbon is racemic because it’s tertiary
Ketone on cyclohexane ->
Reagents: 1) 1 Eq LDA, 2) ketone with a-B alkene, 3) NaOH
1) Deprotonate alpha carbon (forming Enolate Anion)
2-3) Michael Addition, starting material’s alpha carbon is racemic
Cyclize: number the carbon chain so that 6 is the starting material’s carbonyl carbon, the O double-bonded to 6 goes away so double bond with 1 forms (not racemic)
Enamine ->
1) Ketone with a-B alkene
2) H3O+
1) acceptor’s C=C double bond goes away and it bonds with donor’s alpha carbon, donor’s C=C double bond goes away (forming iminium ion)
2) N + its substituents become O, and if there is a tertiary carbon it is racemic
What gives better yields with Gilman Reagent?
1° Haloalkane
Aryl Haloalkane
Steps of Robinson Annulation
Michael Addition -> Aldol Condensation -> dehydrate of aldol product
A) B ketoester
B) Ketone with a-B alkene ->
Reagents: NaOEt, EtOH
Michael Addition
Cyclize: number the carbon chain so that 6 is the starting material’s carbonyl carbon (from ketone), the O double-bonded to 6 goes away so double bond with 1 forms (not racemic), quaternary carbon racemic
1) Ketone on cyclohexane with methyl at alpha position and another ketone at beta position
2) Ketone with a-B alkene
Reagents: NaOH, H2O
Michael Addition
Cyclize: number the carbon chain so that 6 is the starting material’s carbonyl carbon (from ketone), the O double-bonded to 6 goes away so double bond with 1 forms (not racemic), quaternary carbon racemic
In a retrosynthesis problem, how would you recognize an Aldol bond? Michael bond? How would you retrosynthesize?
Aldol bond = a-B alkene
Michael bond = from quaternary carbon, it is the bond that is uniquely within the same ring as the Aldol bond
Retrosynthesize by turning the Aldol bond into a double bond O (separated from Aldol bond ring) + take out Michael bond and make its adjacent bond a double (2 reactants ?)
Malonic Ester ->
Reagents: 1) NaOEt, EtOH
2) Br-CH2-CH2-CH2-CH2-Br
3) NaOEt, EtOH
1) one H goes away by deprotonation
2) deprotonated site grabs substituent by one Br
3) other H goes away by deprotonation
Cyclize: Br goes to deprotonated site and forms a ring (pentagon)
Ester ->
Reagents: 1) DIBALH, -78°C
2) H3O+
O bound to non-carbonyl tail breaks off bound to H (alcohol), 2nd product is gains an H where ester O once was
Reactant: cyclohexane with ketone and alpha racemic methyl
What type of product is formed when the reagent is >1 Eq LDA?
Kinetic Product
Double bond O becomes single bond O-, double bond forms between “carbonyl” carbon and least substituted carbon
Reactant: cyclohexane with ketone and alpha racemic methyl
What type of product is formed when the reagent is >1 Eq LDA?
Thermodynamic Product
Double bond O becomes single bond O-, double bond forms between “carbonyl” carbon and most substituted carbon
What happens to the Kinetic Product in the presence of an excess of ketone?
The reaction becomes reversible to generate a Thermodynamic Enolate Anion
of MO =
of atomic orbital
Conjugated diene
Butadiene (2 terminal alkenes)
Conjugated molecule absorbs light in the ___ region (___-___ nm)
UV-visible (200-700 nm)
Which has a smaller delta E (HOMO-LUMO gap): butadiene or hexatriene?
Hexatriene
Whenever you add HBr to a conjugated diene, what are the 2 possible products?
One double bond goes away, carbocation added to carbon 2
1,2 addition: Br added to carbocation
1,4 addition: double bond shifts over one to the middle/more stable, carbocation added to carbon 4, Br added to carbocation
What is the difference between the Kinetic Product and the Thermodynamic Product formed from the conjugated diene?
The kinetic product has the less substituted alkene, and the thermodynamic product has the more substituted alkene ALWAYS! Regardless of 1,2 or 1,4 addition