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Reactivity At Carbon Centers > carbonyl compounds > Flashcards

carbonyl compounds Flashcards

1
Q

what is the difference between stereoselective and stereospecific?

A

stereospecific is mechanistically bound to produce 1 outcome (can be a mixture of products or only 1 ) while stereoselective produces either or products which is dependent on the conditions

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2
Q

why does hyperconjugation induce partial negativity on one end of the molecule?

A

orbital overlap between the C-H bonds and the pi star of the double bond pushes the electron density to the other end of the molecule

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3
Q

how to determine which alkene is more nucleophilic

A

draw out resonance structures and greater no. of resonance structures = more nucleophilic

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4
Q

what are the 2 types of reaction that are possible with carbonyl substituted alkenes?

A
  1. conjugate addition/1,4- addition
  2. 1,2- addition
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5
Q

what are species with 2 sites of attack called?

A

ambident electrophiles/nucleophiles

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6
Q

what determines the oxidation level of carbons and what effect does it have?

A

if a carbon is bonded to a more electronegative element, then it is more oxidised as electrons are being drawn away from the carbon
and oxidation is known as the loss of electrons

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7
Q

what is the burgi dunitz angle?

A

107 degree of attack of nucleophile to planar C=O pi star orbital

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8
Q

why does a ketone have slower nucleophilic attack compared to aldehydes

A
  1. more steric hindrance at the pi* C=O
  2. due to hyperconjugation the C-H bonds from the methyl groups donate electron density into the pi* of the C=O bond and stabilize it thus making it less prone to nucleophile attack

3.

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9
Q

what is the problem with adding a nucleophile to ketones?

A

sometimes if the R group makes the molecule too sterically hindering, the nucleophile turns into a base instead and deprotonates the molecule to become the enolate ion instead (which is negatively charged thus nu will definitely not attack it anymore)

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10
Q

what happens to the H in C-H when in the presence of a carbonyl group?

A

hyperconjugation donation of electron density into the pi* orbital of the C=O thus the hydrogen loses electron density and becomes more acidic (available for deprotonation)

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11
Q

why would a nucleophilic attack on a carbonyl compound turn from addition to deprotonation?

A
  1. bulky R group
  2. bulky/basic Nu
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12
Q

which is more electron withdrawing, O+ or O

A

O+ because it is more electron deficient thus more willing to draw electrons from the carbon

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13
Q

how to get from a carbonyl to a hemiacetal? 2 reactions

A

acid catalysed reaction: acid that is added to the oxygen then alcohol is added and hydrogen is kicked out in the end
the O in carbonyl is protonated because it is in an acid medium

base catalysed reaction: base deprotonates alcohol to product RO- (alcoxide) and that is added to the carbon in the carbonyl and the H from an ROH is added after

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14
Q

how is the equilibrium between hemiacetals and carbonyl compounds?

A

very little hemiacetal formed

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15
Q

what is the general term for hemiacetals and in what form is the hemiacetal the more produced product?

A

lactol and in an intramolecular addition of hydroxy groups to carbonyl groups

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16
Q

is the hydrogen in hydrides electrophilic or nucleophilic? give an example and reagents it requires

A

“nucleophilic” -> behave like H- but are not actually H-
NaBH4 with methanol
LiAlH4 with diethyl ether

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17
Q

why do organometallic compounds require ether solvents?

A

they can solvate the organometallic compound without reacting with it

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18
Q

what is a grignard reagent?

A

an organometallic compound that consists of a carbon atom bonded to a metal (typically magnesium) and one or more alkyl or aryl groups.

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19
Q

what reagents are used to reduce aldehydes and ketones?

A

organometallic compounds or grignard’s reagent with THF or diethylether (ether containing compound)

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20
Q

what is the difference between organometallic compounds and grignard’s reagent

A

organolithium is a slightly stronger base thus possible deprotonation may occur (grignard is chosen instead because it is a weaker base)

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21
Q

what is formed when organometallic compounds are added to aldehydes and ketones?

A

aldehydes -> secondary alcohol

ketone-> tertiary alcohols

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22
Q

how does a hemiacetal form an acetal? what are the reagents required?

A
  1. protonation
  2. loss of water molecule
  3. add hydroxide
  4. deprotonation

acid catalysed process (less efficient with bases but still possible)

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23
Q

draw out the mechanism for hemiacetal to acetal

A

L18 S8

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24
Q

why is acid based catalyst for hemiacetals better than base?

A

the acid can protonate the OH making it a good leaving group (H2O)

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25
Q

draw out the general structure of an acetal

A

L18 S8

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26
Q

what are the different ways to push the reaction from carbonyls to acetals?

A
  1. increasing the reagents (however if the reagent becomes in excess it is difficult to remove)
  2. remove water using drying agents (MgSO4), molecular sieves or azeotropic distillation
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27
Q

what is the function of producing acetals?

A

because the carbon in acetal is less electrophilic than carbons in carbonyls then conversion occurs to prevent a reaction with carbonyl

(the acetal is then converted back to a carbonyl group after the reaction is complete -> deprotection)

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28
Q

what does deprotectin of acetal to carbonyl involve?

A

acid based catalyst and water

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29
Q

what does the reaction between carbonyls and amines produce? + draw out the mechanism

A

imines L18 S13

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30
Q

what is the pH reaction required for imine and enamine formation and why?

A

pH 4-6 because if it is any more acidic the amine will become protonated

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31
Q

what product does carbonyl and secondary amine produce and why?

A

produces an enamine rather than an imine because it the nitrogen does not have a hydrogen it can lose thus the hydrogen from another carbon atom is lost instead (forms a double bond between a carbon and carbon rather than with carbon and nitrogen)

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32
Q

how does nitrogen effect the polarization of a double cc bond?

A

the lone pair on nitrogen donates electron density into the double bond and polarizes it (good for site of reactivity for electrophiles)

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33
Q

what is the function of the wittig reaction?

A

regiospecificity of double bond formation in a molecule

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34
Q

how is a phosphonium ylide formed?

A

deprotonation of phosphonium salt with a base

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35
Q

draw out the mechanism for wittig reaction

A

L18 S15

36
Q

how is the phosphonium salt made?

A

SN2 reaction with alkyl halide and triphenylphosphene

37
Q

what products are formed for a reaction between a phosphonium ylide and aldehyde?

A

if unstable ylide (strong base): z-alkene formed
if stable ylide (weak base): e-alkene formed
selective not specific reaction

38
Q

what does the stabilization of phosphonium ylides depend on?

A

whether the R group is electron withdrawing or electron donating

39
Q

what is more reactive: ketones or aldehydes and why?

A

ketones are less reactive as they have greater steric hindrance and there is more electron donation into the anti-bonding orbital of the C=O through hyperconjugation (thus the site of reactivity becomes less electrophilic)

40
Q

what are the issues with the wittig reaction?

A
  1. isomeric alkenes (especially if the R’ and R groups are similar) are difficult to separate and produces yield problems)
  2. by product triphenylphosphine can be difficult to separate
41
Q

what is the type of reaction that occurs with carboxylic acid derivates and nucleophiles?

A

stepwise reaction with addition then elimination

42
Q

what is the addition step required for reactions between carboxylic acid derivates and nucleophiles if the nucleophile is neutral rather than charged?

A

deprotonation with a base
Nu-H

43
Q

why are there 2 bands shown in IR for anhydrides?

A

antisymmetric and symmetric stretch

44
Q

why IR value of a carbonyl bonded to a nitrogen less than a carbonyl bonded to an oxygen?

A

nitrogen is less electronegative thus more willing to donate its electron density into the pi star orbital of C=O which weakens it into less than double and more single-like bond

  • they can donate because the orbitals invovled (nb and pi antibonding align almost syncoplanar to each other)
44
Q

why is the C=O bond with chlorine resembling a triple bond?

A

alignment of non bonding oxygen to C-Cl antibonding allows for electron donation into the orbital creating a semi-triple bond between C and O

45
Q

what is the reaction site for electrophiles in amides and why?

A

on the oxygen due to the loss of nucleophilicity of nitrogen as lone pairs are being partially donated into the antibonding of the C=O pi star

*for this reason oxygen in an amide is also more basic than the nitrogen

46
Q

how does the pKa effect the relationship between the leaving group and the molecule’s reactivity towards nucleophiles

A

if the pKa of an acid is low, then it will more likely dissociate into its ions (aka leaving group becomes more stable) thus has higher reactivity towards nucleophiles

eg. HCl readily dissociates into H+ and Cl- thus Cl- is a good leaving group

47
Q

what do acid chlorides react with alcohols to make (+reagents required) and what is the mechanism?

A

acid achloride + hydroxide + base -> ester + HCl that is neutralized

A BASE IS REQUIRED BECAUSE HCL IS A STRONG ACID WHICH CAN FURTHER REACT WITH THE MOLECULE

and L19 S10

48
Q

what do acid chlorides and amines react to make and what is the mechanism?

A

2 amine molecules with 1 acid chloride to form amide + salt

49
Q

why do 2x the amine need to be added?

A

amine is not only a nucleophile but also a good base, thus can deprotonate the molecule instead (more reagent added for more product)

50
Q

what catalyst can be used in the acid chloride and amine reaction and what is its benefits?

A

pyridine is used because it can also act as a base and it is easy to get rid of the pyridinium chloride salt formed (either through washing with copper sulfate or acid washing)

51
Q

how are acid chlorides made? + draw mechanism

A

carboxylic acids and thionyl chloride

L19 S12

52
Q

how are carboxylic esters synthesized? what are the reagents?

A

condensation reaction between carboxylic acids and alcohols

alcohol + carb acid and acid catalyst

53
Q

draw mechanism of esterification with carboxylic acids, is the reaction reversible or irreversible?

A

L19 S13

in equilibrium

54
Q

what is the mechanism/reagents used for hydrolysis of carboxylic esters?

A
  1. acid catalyst and water and L19 S14
  2. basic catalyst with water L19 S15
55
Q

what is more reactive, esters or aldehydes and ketones and why?

A

esters are less reactive as the oxygen donates electron density into the pi star of the carbonyl bond making the carbon less electrophilic

56
Q

what is the problem with doing SN2 on alkyl halides to form tertiary amines and what is the other way to do it?

A

overalkylation of amine because amine itself is a good nucleophile when regenerated so it reacts with another alkyl halide again

an alternative method is to react acid chloride with base to form a amine and reduce the amine with lithium aluminium hydride to form the tertiary amine

57
Q

why is THF not used as a solvent?

A

it readily forms peroxides which are explosive

58
Q

draw the mechanism for the oxidation of primary alcohols to carboxylic acids with chromic acid catalyst

A

L20 S12

59
Q

is chromic acid selective towards oxidation reactions?

A

no primary alcohol will not stop after aldehyde is formed normally goes straight to carboxylic acid

60
Q

what reagents can we use if we want the reaction to stop at aldehyde instead of carboxylic acid? why is it milder?

A

pyridinium dichromate or pyridinium chlorochromate
there is a base so acid is not as strong (buffers the acidic proton) and doesnt further react with the aldehyde to form the second chromate ester

61
Q

what is the RDS of the oxidation of alcohols?

A

redox reaction when the chromate ion is spit out

62
Q

when can tertiary alcohols be oxidized

A

when there is an allylic hydroxyl group (the hydroxyl group is 2 carbons away from a double bond)

63
Q

what are the 2 rules with turning ketones to esters?

A

the more substituted side of the carbon will make room for the oxygen

the C-O migration is stereospecific thus the configuration of the products and reactants is the same

64
Q

what happens when a tertiary alcohol is reacted with a stronger acid?

A

OH group is protonated to form a good leaving group in water and elimination reaction occurs to form double bond

65
Q

what are the 2 ways to produce nitriles?

A
  1. from primary amides and lose water (using dehydrating agents eg. POCl3 and P2O5)
  2. from haloalkanes and sodium cyanide (SN2) reaction
66
Q

what is a reaction that adds a new C-C bond called?

A

homologation reaction

67
Q

draw our the mechanism for the dehydration and hydration of primary amides to form nitriles

A

L21 S8-9

68
Q

can you draw the mechanism behind converting a haloalkane to a ketone

A

L21 S9

69
Q

compare DIBAL to LiAlH4

A

DIBAL is more selective compared to LiAlH4 thus less reductive

LiAlH4: nitrile to primary amine
DIBAL: nitrile to aldehyde

70
Q

what is the word for reversible polarity?

A

umpolung

71
Q

what is the relationship between the enol tautomer and the enolate anion?

A

enol tautomer (neutral) is the conjugate acid of the enolate anion (negatively charged)

72
Q

draw out the mechanisms for acid and base catalysed keto-enol tautomerism

A

L21 S14-15

73
Q

what are the relative acidities and basicities required by reactants and products for a carbonyl to form the enolate anion?

A

B-H must be a weaker acid than the carbonyl

B must be a stronger base than the enolate anion

74
Q

what are the 2 types of reaction that can occur on an enolate anion?

A

O-alkylation: enol ether
C-alkylation: carbonyl compound

75
Q

how does electropositivity of a metal effect the alkylation in an enolate anion reaction?

A

more electropositive -> more ionic -> more likely to react on oxygen -> O-alkylation

less electropositive -> more covalent -> more likely to react on double bond -> C-alkylation

76
Q

how do soft/hard leaving group effect the type of alkylation reaction for enolate anion?

A

soft: C-alkylation
hard: O-alkylation

77
Q

why do ether solvents work well with lithium enolates and how does that help with C-alkylation?

A

lithium loves oxygen so it surrounds the electronegative oxygen, it is relatively small in size so it can solvate the oxygen which decreases the reactivity of the oxygen so the alkylation occurs at the carbon instead

78
Q

how does the size of the base effect the alkylation site?

A

sterically hindered/bulky base would be a bad nucleophile thus would not react with the carbon in the carbonyl and would deprotonate the hydrogen instead to form enolate anion

79
Q

what are the 2 ways to react nucleophilic enolates with carbonyl compounds and what is their mechanism?

A

L22 S12

80
Q

what synthetic benefits would there be to use a beta ketoester instead of a ketone only?

A

beta ketoester enolate anion is easier to generate and more stable (due to more delocalization of electrons)

the enolate is much less basic compared to the ketone enolate

81
Q

what is the benefit of lowering the basicity of a nucleophile?

A

remove the probability of an elimination reaction

82
Q

how can you make an alkene electrophilic?

A

adding an EWG next to it

83
Q

what are the 2 types of anions that can be formed with adding a nucleophile to unsaturated carbonyl

A

1-4 addition: enolate anion
1-2 addition: alkoxide

84
Q

what determines the electrophilicity of the carbon in the carbonyl?

A

the substituents next to it

bond strength of carbonyl depends on:
if more donation from double bond to single bond anti then more triple bond behaviour

if more donation from single bond to double bond anti then more single bond behaviour

85
Q

draw out the baeyer villiger reaction (ketone to ester)

A

check L20 second lasts slide

86
Q

enamine soft or hard and what does it mean that it can react with?

A

enamine is classified as soft therefore it can react with unsaturated compounds (aka the carbon)

Reactivity At Carbon Centers (8 decks)

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