Organic Chemistry

Front 1

What is a Weinreb amide used for? Draw the mechanism.

Back 1

Attach a nucleophile to a carbonyl.
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Front 2

How would a hydroxyl group be converted to a bromide? Draw the mechanism.

Back 2

PBr3
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Front 3

How would one attach a methyl carbonyl to a molecule?

Back 3

Attach nucleophilic alkyne (LiCCH)
FGI to methyl carbonyl with HgO and H2SO4

Front 4

What reagent is used to reduce carboxylic acids to alcohol? Draw the mechanism.

Back 4

BH3 (in THF)
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Front 5

What reagent is used to reduce an amide to an amine? Draw the mechanism.

Back 5

BH3 (in THF)
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Front 6

What reagent is used for reductive amination? Draw the mechanism.

Back 6

NaBH3(CN)
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Front 7

How would one reduce an ester to an aldehyde? Draw the mechanism.

Back 7

DIBAL
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Front 8

How would one attach an aldehyde to a molecule? Draw the mechanism.

Back 8

Use nucleophilic cyanide (NaCN) to attach to molecule and reduce with DIBAL
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Front 9

How would one oxidise an alcohol to an aldehyde? Draw the mechanism.

Back 9

Add TPAP in catalytic amounts. Regenerate with NMO.
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Front 10

How would one oxidise a molecule completely?

Back 10

Na2Cr2O7 or KMnO4

Front 11

What is OsO4 used for? Draw the mechanism.

Back 11

Syn-dihydroxylation of alkenes.
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Front 12

Draw the mechanism for epoxidation.

Back 12

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Front 13

Draw the mechanism for ozonolysis. Which reagents yield which products?

Back 13

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Me2S => aldehyde
H2O2 => carboxylic acid
NaBH4 => alcohol

Front 14

How are ketones and aldehydes protected? Draw the mechanism.

Back 14

With diols, catalysed by para-toluene sulphonic acid and removal of water.
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Front 15

What would one react a dithiol with? Why is this useful?

Back 15

A carbonyl to form a dithiane.
Dithiane can then react with BuLi to reverse polarity of carbon. Dithiane removed with Hg2+/H2O.
Overall reaction = electrophile added to carbonyl carbon.

Front 16

How are alcohols protected? Give the mechanism.

Back 16

With trialkylsilylchlorides, activated by imidazole. Removed with TBAF.
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Front 17

How are phenols protected?

Back 17

With MeBr. Remove with HBr.

Front 18

How are amines protected? Draw the mechanism.

Back 18

With BOC. Removed with TFA.
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Front 19

What do the benzyl and carboxybenzyl groups protect? How are they removed? Draw the mechanism.#s.

Back 19

Amines and alcohols.
Removed with H2 and Pd/C.
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Front 20

Draw the mechanism of the Diels-Alder reaction. What type of molecules can be disconnected back to the Diels-Alder product? Draw the disconnection.

Back 20

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1,6-dicarbonyls
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Front 21

Which isomer is the major product in a Diels-Alder reaction? Why?

Back 21

Endo isomer.
Reaction is irreversible so is kinetically controlled. Endo forms faster due to stabilisation caused by secondary orbital overlap.

Front 22

What are Baldwins rules? Which rings reactions are favourable?

Back 22

Endo = broken bond in ring, Exo = broken bond outside ring.
tet = sp3, trig = sp2, dig = sp

6/7-endo-trig, 3/4/5/6/7-endo-dig
3/4/5/6/7-exo-tet, 3/4/5/6/7-exo-trig, 3/4-exo-dig

Front 23

What is the Felkin-Ahn model?

Back 23

Explains the relative stereochemistry of products from nucleophilic addition to a carbonyl.
Put largest/most electronegative group 90 degrees to carbonyl, nucleophile approaches 107 from carbonyl from least hindered side.

Front 24

How can the stereoselectivity of nucleophilic attack of carbonyls be reversed? Give an example.

Back 24

Chelation control. Metal ion chelates carbonyl and other heteroatom with lone pair.

Reduction of phenyl ketone adjacent to thioether by LiBH4 yields syn product, reduction with Zn(BH4)2 yields anti product

Front 25

How is the stereochemistry of the aldol reaction controlled?

Back 25

Cis enolates yield syn-products
Cis enolate made from Bu2BOTf and iPr2NEt

Trans enolates yield anti-products
Trans enolate made from c-hex2BCl and NEt3

Front 26

Draw the reaction mechanism for the Wittig reaction. How is stereochemistry controlled?

Back 26

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Stabilised ylides favour the trans isomer.
Unstabilised ylides favour the cis isomer.

Front 27

How is the Horner-Wadsworth-Emmons reaction different from the Wittig reaction? What advantages does it have?

Back 27

Uses phophonate ester instead of ylid. Is E-selective.

Purification easier.

Front 28

Draw a general metathesis mechanism.

Back 28

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Front 29

What are the formula of Grubb's first catalyst?

Back 29

1st: Ru(Cl)2(PCy3)2(CHPh)

Front 30

What types of chirality exist?

Back 30

Central chirality
Planar chirality
Axial chirality

Front 31

What is the equation for enantiomeric excess?

Back 31

%e.e. = ((S-R)/(S+R))*100

Front 32

What are the equations for specific rotation and optical purity?

Back 32

[alpha] = alpha/(c*l)
OP = ([alpha(measured)]/([alpha(pure)])*100

where alpha = measured rotation, [alpha] = specific rotation

Front 33

Why is iodolactonisation stereospecific? Draw the mechanism.

Back 33

Iodonium has to be behind plane of ring.
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Front 34

How is the Evans auxiliary added/removed? What reactions can it be used in? Why does it only give enantiomer in these cases?

Back 34

Deprotonate auxiliary with BuLi, add reactant in form of acyl chloride. Remove with NaOMe.

Diels Alder - Lewis acid induces conformational lock such that diene can only approach from one side.
Aldol - carbonyl can only approach from one side do to sterics.

Front 35

How are ketones asymmetrically reduced? Draw the mechanism.

Back 35

CBS and BH3

Front 36

How is asymmetric syn-dihydroxylation acheived?

Back 36

Reaction with OsO4 and either DHQD or DHQ

Front 37

Draw the mechanism of the diselenide radical MCR.

Back 37

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Front 38

Draw the mechanism of the boronate MCR.

Back 38

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Front 39

Draw the mechanism of isocyanide formation.

Back 39

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Front 40

What reactants does the Passerini reaction involve? Draw the mechanism.

Back 40

Carboxylic acid, aldehyde, isocyanide
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Front 41

What reactants does the Ugi reaction involve? Draw the mechanism.

Back 41

Isocyanide, carboxylic acid, amine, carbonyl
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Front 42

Draw the mechanism of the thermal azide/alkyne reaction.

Back 42

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Front 43

What triazole is formed using a Cu(I) catalyst? Draw the mechanism.

Back 43

1,4-triazole
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Front 44

What triazole is formed using the Ru catalyst? Draw the mechanism.

Back 44

1,5-triazole
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Front 45

What does Heck coupling do? What catalyst is normally used? What bases are used? Draw the mechanisms.

Back 45

Couple an alkene and a halide/triflate.
Pd(OAc)2
Et3N or Ag3PO4
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Front 46

What does Stille coupling do? Draw the mechansim.

Back 46

Links a halide with alkyl tin.
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Front 47

What does Suzuki coupling do? How is the reactant activated? Draw the mechanism.

Back 47

Couple a halide with organoboron.
Boron activated by OH-
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Front 48

What does Sonogashira coupling do? Draw the mechanism.

Back 48

Couple a halide with a terminal alkyne.
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Front 49

What does the Buchwald-Hartwig coupling do? Draw the mechanism.

Back 49

Couple an amine with a halide.
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Front 50

What does Negishi and Kumada coupling do? Draw the mechanism.

Back 50

Couples a Grignard reagent with an aryl halide.
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Front 51

Draw the mechanism of Pd-catalysed allylic substituion. What catalyst is used?

Back 51

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Pd(PPh3)4 pre-catalyst, Pd(PPh3)3 catalyst

Front 52

What reagents are used to convert alcohols to sulfides? Draw the mechanism.

Back 52

Harpp's reagent (succinimide anion and SPh cation)
PBu3
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Front 53

What type of reaction is the Sommelet rearrangement? What conditions are used? Draw the mechanism.

How is the Stevens reaction different? Draw the mechanism.

Back 53

[2,3]-sigmatropic rearrangement
-78 degrees
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Performed at warm temperatures.
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Front 54

What reagents are used to interconvert between allylic alcohols and sulphenic esters? What is the sulphenic ester in equilibrium with? Draw the mechanism.

Back 54

Forward: base, ArSCl
Reverse: MeOH

Sulfoxide
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Front 55

What is produced by heating a sulfoxide? What type of reaction is this? Draw the mechanism.

Back 55

Alkene
Syn-elimination
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Front 56

What intermediate is characteristic of the Pummerer rearrangement? Draw the mechanism.

Back 56

C=S+
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Front 57

What does Kornblum oxidation do? Draw the mechanism.

Back 57

Convert an alkyl halide to an aldehyde.
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Front 58

What does Swern oxidation do? What conditions are used? Why? Draw the mechanism.

Back 58

Converts an alcohol to an aldehyde.
-60 degrees.
Otherwise Pummerer rearrangement occurs.
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Front 59

What does the Julia reaction do? Draw the mechanism.

Back 59

Make an E-alkene from sulphone.
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Front 60

What does the Ramburg-Backlund reaction do? What are advantages and disadvantages? Draw the mechanism.

Back 60

Converts a sulphone with built in leaving group into an alkene.
Can form strained or highly substituted double bonds. But is not stereoselective.
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Front 61

What is the cheletropic elimination of SO2? Draw the mechanism.

Back 61

Heating of some sulphones results in elimination of SO2, giving a 1,3-diene.
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Front 62

How do different types of sulphur ylid result in different products? Draw the mechanism of reaction with an enone.

Back 62

Stabilised ylids giving thermodynamic product, while unstabilised ylids give kinetic product.
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Front 63

What does the Baeyer-Villiger reaction do? Draw the mechanism.

Back 63

Converts carbonyl to ester by alkyl migration.
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Front 64

What does the Corey-Winter reaction do? What is this the opposite of? Draw the mechanism.

Back 64

Converts a syn-diol into a cis-alkene.
Opposite of OsO4 syn-dihydroxylation.
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Front 65

Which carbon ions does silicon stabilise?

Back 65

alpha-carbanion
beta-carbenium

Front 66

Draw the mechanism of the sila-Pummerer reaction.

Back 66

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Front 67

What does the Peterson reaction? How are different eliminations acheived? Draw the mechanism.

Back 67

Make an alkene by elimination of Si and O.
Use NaH for syn-elimination, use H3O+ for anti-elimination.
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Front 68

What does the Shapiro reaction do? How is this useful? Draw the mechanism.

Back 68

Makes a vinyl anion.
Making vinyl silanes.
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Front 69

How are allyl silanes made?

Back 69

Allyl halides. Make anion using Na, add Me3SiCl.

Front 70

What is the difference in reactivity between vinyl and allyl silanes?

Back 70

Vinyl silanes are resistant to nucleophilic cleavage.
Allyl anions are relatively stable so allyl silanes can be cleaved.

Front 71

Which two methods are used to make vinyl silanes from silyl acetylenes? What is the stereochemistry of the products in both cases? Draw the reaction scheme.

Back 71

H2/Pd or DIBAL
Cis
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Front 72

What is the Ireland-Claisen reaction? Draw the mechanism.

Back 72

A modification of the Claisen reaction using a silane to control specificity, which is equatorial in the transition state.
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Front 73

How does silicon affect ozonolysis?

Back 73

Silyl enol ether reacts prefentially over other alkenes.

Front 74

How does silicon affect epoxidation? Draw the mechanism.

Back 74

Silyl enol ethers can be alpha-oxidised.
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Front 75

How are enones made from silyl enol ethers?

Back 75

Oxidation with Pd(OAc)2 catalyst.

Front 76

What is the Mukiaiyama reaction? Draw the mechanism.

Back 76

Reaction of acetal with TiCl4 to make electrophile for silyl enol ether.
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Front 77

How are selenium electrophiles and nucleophiles made?

Back 77

Both from diselenide.
Electrophile: reaction with Br2 to give PhSeBr
Nucleophile: reaction with NaBH4 to give PhSeNa

Front 78

Draw the mechanism using selenium to make an enone from a ketone.

Back 78

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Front 79

How are alcohols converted to selenides? Draw the mechanism.

Back 79

Activation of selanocyanate with PBu3.
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Front 80

Draw the mechanism for electrophilic selenium attacking an alkene.

Back 80

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Front 81

How is SeO2 converted to a syntheically useful compound?

Back 81

Hydration with H2O or ROH to give selenious acid.

Front 82

Draw the mechanism of allylic hydroxylation.

Back 82

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Front 83

Draw the mechanism of using selenious acid to make alpha-diketones.

Back 83

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Front 84

What does the Mitsunobu reaction do? Draw the mechanism.

Back 84

Invert alcohol stereochemistry.
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Front 85

What is the Corey-Fuchs reaction? Draw the mechanism.

Back 85

A special case of the Wittig reaction used to make a terminal alkyne from CBr4.
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Front 86

What does the Seyferth-Gilbert reaction do? Draw the mechanism.

Back 86

Convert aryl ketones to substituted alkynes.
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Front 87

What reaction is the Bestmann modification a modification of? Why is it better? What is it commonly used for? Draw the reaction scheme.

Back 87

Seyferth-Gilbert reaction.
Milder conditions.
Making terminal alkynes from aldehydes.
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