Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Organic Chemistry > Carbonyls > Flashcards

Carbonyls Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

what does a carbonyl bond consist of?

A

one strong σ bond + a weaker π bond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

lactone

A

cyclic ester

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

lactam

A

cyclic amide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Burgi-Dunitz angle

A

Nu approaches @ 107

more efficient + reduced repulsion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Nu addition to carbonyl - electronics

A

Nu donates pair of electrons into π* orbital of C=O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

how does delocalisation affect reactivity?

A

more delocalisation = less reactive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

delocalisation definition for carbonyls

A

ability for heteroatom’s lone pair to donate into carbonyl carbon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is the balance between when comparing different carbonyl systems?

A

electronegativity of leaving group (δ+ on carbonyl) and donation of e- back into pi system

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

why are esters more reactive than amides?

A

N = less electronegative -> donates much more e- density back into pi system
= smaller δ+ on carbonyl

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

link between pKa and leaving groups

A

lower pKa = more stable conjugate base = better leaving group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

why are aldehydes more reactive than ketones?

A
  1. INDUCTIVE EFFECT

R groups = inductive
ketone has 2 R groups
more e- density pushed back on C=O
smaller δ+ on carbonyl carbon

  1. STERICS

carbonyl carbon on ketone = more statically hindered

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is acid strength affected by?

A
  1. strength of HX bond
  2. stability of conjugate base
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

reactivity of carbonyls - δ+ carbon

A

electrophilic - Nu reacts here

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

reactivity of carbonyls - δ- oxygen

A

lewis basic - reacts with acids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

reactivity of carbonyls - acidic alpha-proton

A

deprotonates to form v. stable bases

remaining base = nucleophilic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

oxidation level

A

no. of heteroatoms attached to carbon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

problem with Jones oxidation

A

use of chromium = v. toxic (2 eq of waste)

acidic conditions - chemoselectivity issues [acid could react with other FGs]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

problem with potassium permanganate

A

2 eq of manganese waste - not as toxic though

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

chemoselectivity

A

which FG will react

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

regioselectivity

A

where it will react

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

stereoselectivity

A

how it will react

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

why is it difficult to stop oxidation at aldehyde?

A

water -> forms hydrate, which can oxidise further

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

problem with PCC reaction?

A

not very green - chromium waste

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

advantage of Ley oxidation

A

organic oxidising material -> waste easier to deal with

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

disadvantage of Ley oxidation

A

stoichiometric DMP waste

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

temperature + reasoning of Swern oxidation

A

-78

must be v. cold as the reaction is v. exothermic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what happens if a molecule has x2 different carbonyl groups?

A

only 1 will react (the more reactive one)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

metal hydrides

A

source of H-

LiAlH4 - LiBH4 - NaBH4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Lewis acid hydrides

A

neutral Lewis acids

only become source of H- when they form Lewis acid-base complex

useful for reduction of e- rich derivatives

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

why won’t a carboxylic acid never reduce to just an aldehyde?

A

intermediate = too reactive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

organometallic reagents

A

lithium/magnesium derived

make new C-C bonds

not ionic but covalent

v. strong nucleophiles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

which compound will not work with organometallic reagents?

A

alkyl halides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

which functional groups need to be protected when using organometallic reagents?

A

carbonyls + acids

because grignards = v. nucleophilic and basic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Wittig reaction - forming E alkenes

A

stabilised phosphorus ylid - has EWG adjacent to P group

approach of ylid + aldehyde = key (ORBITAL SYMMETRY)

keeps large sub. apart - STERICS [reduces energy]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Wittig reaction - forming Z alkenes

A

unstabilised phosphorus ylid - has NO EWG adjacent to P group

electrostatics keep sub. apart (less repulsion = lower in energy)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

carboxylic acids - properties

A

lewis basic lone pair -> more delocalisation into π system

acidic proton -> more EW R groups = more acidic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

why might we want to convert an acid chloride to an acid anhydride?

A

although acid chloride = more reactive, it’s prone to hydrolysis

[acid anhydride]

-delocalisation over more atoms
-resonance on one of C=O is less strong (therefore inductive effect is stronger, larger δ+)

= MORE STABLE BUT LESS REACTIVE

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

ester - properties

A

electrophilic @ C=O

more e- withdrawing R group = more acidic the proton

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

problems with condensation reaction to produce ester?

A

requires v. harsh conditions - high heat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

problems with Steglich reaction?

A

urea = product

v. insoluble and hard to remove

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

benefits of protonating ester in acid hydrolysis?

A

O has given up 2 e- to form bond -> wants e- density back

pulls e- back from C=O = INCREASED ELECTROPHILICITY

LUMO lower in E = easier reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

benefits of v. low or high pH in acid hydrolysis?

A

[specific acid/base catalysis]

rate = fastest @ extremes

low pH = more oxonium
high pH = lots of -OH = better Nu than H2O (HOMO higher in E)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

which ester is stable against both acid and base catalysis?

how can it be removed?

A

tera-butyl esters

act as PROTECTING GROUP

removed under dry acid conditions

44
Q

why does using DIBAL stop reduction at aldehyde?

A

forms tetrahedral intermediate

@-78C tetrahedral intermediate won’t react until H+ work up (will then collapse)

45
Q

amide - properties

A

electrophilic @ C=O

acidic α-proton => pKa ~ 35

acidic N-H => pKa ~ 25

46
Q

evidence for addition with loss of oxygen reaction

A

isotopic labelling of O (e.g. using O18)

47
Q

acetals / hemiacetals

A

1 mol of alcohol -> hemi-acetal

2 mol of alcohol -> acetal

48
Q

ketone equivalent of acetal

A

ketal

49
Q

how to increase rate of formation of hemiacetals

A

base or acid catalysis

ACID - reacts with Lewis base l.p. on carbonyl to protonate it = OXONIUM formation [v. electrophilic; increased δ+ = more susceptible to nucleophilic attack]

BASE - deprotonates alcohol -> alkoxide [= more nucleophilic]

50
Q

what is the rate determining step of hemiacetal formation?

A

nucleophilic attack @ C=O

by increasing reactivity of C=O, RoR also increases

51
Q

how to prevent reaction from reversible when forming acetals

A

removal of water

e.g. molecular sieves, MgSO4, Dean-Stark

52
Q

Baeyer-Viliger reaction -> what would happen if an unsymmetrical ketone was used?

A

more sub. group attached to alpha-carbonyl = better at stabilising C+ = better at migrating

53
Q

problems with protecting groups

A

each additional step reduces atom economy

= reduction in efficiency of reaction

= reduced yield

54
Q

removal of acetal protecting group

A

acid hydrolysis

55
Q

removal of dithiane protecting group

A

[stable to acid hydrolysis]

Raney Ni; H2 -> alkane

HgCl2; H2SO4; H2O -> original carbonyl

56
Q

problem with diamines

A

v. difficult to remove

57
Q

imine formation

A

aldehyde/ketone + primary amine

58
Q

optimum pH for imine/enamine formation

A

[4-6]

too acidic = protonates amine -> ammonium salt = no longer nucleophilic

too basic = favours forward reaction, not enough acid to protonate intermediate for loss of water

59
Q

what must be present for an imine/enamine to form?

A

alpha-hydrogen in carbonyl species

otherwise, iminium ion is formed instead

60
Q

what do enamines behave like?

A

alkenes

61
Q

problem with mixing an amine with an alkyl halide

A

not controlled

alkylated amine = more nucleophilic than starting amine (will react instead)

62
Q

why is the ketone/imine form favoured over the enol/enamine?

A

C=O bond is more stable (stronger) than the C=C

63
Q

why is it beneficial to form 1,3-dicarbonyl?

A

shifts the keto-enol equilibrium to the right (enol = spectroscopically visible)

[reasons]

  • additional C=O bond = more stability
  • OH group can H bond to oxygen in C=O (forms 6-membered ring) - CONJUGATION
64
Q

what other way can we force the keto-enol equilibrium to the RHS?

A

acid catalysis

65
Q

where is the largest orbital in the ground state structure of the enol?

A

on oxygen (where -ve charge is)

66
Q

where is the largest orbital in the reactive state structure of the enol?

A

on carbon (reacts via carbonyl)

67
Q

enolate + hard electrophile =

A

addition to oxygen

68
Q

enolate + soft electrophile =

A

addition to carbon

69
Q

what must happen for deprotonation to occur?

A

C-H bond must align with p-orbital of C=O pi-bond

70
Q

kinetic enolate

A

[LHS of eq]

less sub. + stable

PREFERS -
strong, hindered base
low temp (-78)
short reaction time

71
Q

reasoning for kinetic enolate conditions

A

trying to make reaction irreversible

by adding ketone to base, base is always in excess => reaction is one-way

72
Q

thermodynamic enolate

A

[RHS of eq]

more sub. + stable

PREFERS -
excess ketone
higher temp.
long reaction time

73
Q

consequences of enolisation

A
  1. CONJUGATION
    -enolate in conjugation with alkene ∴ addition occurs at γ rather than α/β
    -product = more stable than starting carbon

2.RACEMISATION
-any stereogenic centre next to C=O would be destroyed (like in Sn1 reactions)

74
Q

α-halogenation - ACIDIC CONDITIONS

A

MONO-α-halogenation

[reason]
-reaction happens via l.p. on C=O
-after 1st halogenation, l.p. = less Lewis basic/nucleophilic
-slows down RDS further
-having Br (EWG) disfavours enol formation -> pushes eq. LHS

  • acid regenerated
75
Q

α-halogenation - BASIC CONDITIONS

A

MULTIPLE-α-halogenation

[reason]
- x2 α protons = more acidic than 3 in starting material
-adding I drops acidity
-end product = I3 = v. good leaving group (can therefore directly produce carboxylic acid)

76
Q

where will polar aprotic solvents promote reactions?

A

@ oxygen

77
Q

where will ethereal solvents promote reactions?

A

@ carbon

78
Q

where will larger enolate counter ion promote reactions?

A

@ oxygen

79
Q

which enolate will Li form?

A

kinetic / 1,2

80
Q

enolate formation in aldehydes?

A

aldehydes = too reactive

self-condense

81
Q

how to prevent esters reacting with themselves (i.e. Claisen condensation)

A

keep cool (-78C)

82
Q

which proton will react first in carboxylic acids?

A

OH (more acidic than CH)

produce double deprotonated compound = Iwanow intermediate

83
Q

where will acyl chlorides + aldehydes favour attack?

A

@ C=O [1,2]

84
Q

where will ketones favour attack?

A

form mixture of regioisomers of 1,2 and 1,4

85
Q

where will esters + amides favour attack?

A

1,4

86
Q

what can you use to to force NaBH4 to reduce C=O instead of the alkene in the molecule?

A

CeCl3

= Luche reduction

87
Q

which enolate will K / Na form?

A

thermodynamic / 1,4

88
Q

what is an aldol reaction?

A

new C-C bond formed from α-carbon to carbonyl carbon

89
Q

what does an aldol reaction require?

A

enolate/enol + electrophilic carbon species

90
Q

why is the alcohol deprotonated first in acid catalysed aldol reaction?

A

more basic

91
Q

when can self-condensation occur?

A

carbonyl group (C=O) acts both as the electrophile and the nucleophile in an aldol condensation

more than 1 set of acidic protons

92
Q

cross-condensation

A

aldol reaction between 2 different carbonyl species

4 possible aldol products

93
Q

for crossed condensation to work well, what are the conditions that must be met?

A
  1. one carbonyl must be capable of enolisation
  2. the other carbonyl must be incapable of enolisation + MORE electrophilic than its enolisable partner
94
Q

specific enol equivalents

A

have reactivity of enols/enolates

helps form enol in one sitting + then react with choice of electrophile to stop at aldol product

95
Q

lithium enolate + aldehydes

A

too reactive - will quickly self-condense

96
Q

why does the Makaiyama aldol reaction / silyl enol ether reaction need a lewis base

A

less reactive than lithium enolates

lowers LUMO of C=O

97
Q

when can an intermolecular aldol reaction occur?

A

when a molecule contains x2 ketones

98
Q

when there is >1 enolisation site, which ring size is most likely to form?

A

5 or 6 membered rings = most thermodynamically stable

as ring size gets smaller, strain on carbons = greater

99
Q

requirements for Robinson annulation

A
  1. enolisable carbon derivative
  2. Michael acceptor
100
Q

what to look out for when choosing which product/enolisable site to use during Robinson annulation (usually >1)

A

make sure there’s acidic protons in dehydration step

think about conjugation -> pi system must be planar to carbonyl

101
Q

benefit of using non-enolisable ester molecule in Claisen reaction?

A

only forms 1 product

102
Q

why is oxalate the most reactive non-enolisable ester?

A

2 EWGs (EtO)

combination of the 2 LUMOs
-> one raises in energy
-> other drops in energy

103
Q

Dieckmann condensation - reagents

A

alcohol and base must match esters on either side of starting molecule

prevents transesterification reactions

104
Q

Knoevenagel reaction - choice of amine

A

primary/secondary forms iminium with aldehyde/ketone

tertiary doesn’t react

105
Q

why is the cyclic form of D-glucose most favourable?

A

usually for acetal reactions, it is entropically unfavourable (decreased disorder; -ve ΔS)

cyclic = intramolecular reaction (ΔS is no longer negative) = favourable reaction

Organic Chemistry (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions