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Organic Chemistry > Reaction Mechanisms > Flashcards

Reaction Mechanisms Flashcards

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1
Q

Strong Nucleophiles

A

want positivity
CH3ONa - Methoxide
NaOH - Hydroxide
NaOR - Alkoxide
NaX - Halide
NaSH - Thiolate
R2C=CR2 - Alkene
T-BuO - Tertbutoxide (bulky)

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2
Q

Weak Nucleophile

A

CH3CH2OH - ethanol
H2O
CH3OH - methanol
T-BuOH - tert-butanol

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3
Q

Electrophiles

A

Alkyl halides
Carbocations

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4
Q

SN2 Reactions are
reagents are

A

concerted substitution reactions
involves a strong nucleophile (weak base) and a 1° or 2° (minor)

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5
Q

reaction when there is a weak base and a weak nucleophile

A

no reaction

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6
Q

E2 reactions are

A

concerted elimination reaction (H removed to form alkene)
involves a strong base (weak or strong nucleophile) and a 2° (major) or 3° alpha carbon
or any reaction with heat

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7
Q

SN2 products stereochemistry

A

enantiomeric configuration of reagent

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8
Q

E2 products stereochemistry

A

most stable alkene will be major product (Zaitsev) and less stable will be minor (Hoffman)
Unless there is a bulky base, then Hoffman product is favored

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9
Q

Stereospecificity of E2 reactions

A

H that forms bond must be anti from leaving group

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10
Q

SN1/E1 intermediate is
when to rearrange

A

carbocation
find the most stable intermediate

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11
Q

in solvolysis the solvent is

A

the nucleophile

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12
Q

E2 reagents

A

Strong base, weak nucleophile
NaH
DBN
DBU

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13
Q

SN2/E2 reagents

A

Strong base, strong nucleophile
-OH, MeO-, EtO-

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14
Q

SN1/SN2 reagents

A

Weak base, strong nucleophile
Halide ions, RS-, HS-, RSH, H2S

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15
Q

SN1/E1 reagents

A

weak base, weak nucleophile
H2O, MeOH, EtOH

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16
Q

With a strong base/weak nucleophile and 1°/2°/3° the reaction will be

A

E2

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17
Q

With a strong base, strong nucleophile 1° reaction will be

A

SN2 major, E2 minor unless heat is applied

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18
Q

With a strong base, strong nucleophile 2° reaction will be

A

E2 major, SN2 minor

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19
Q

With a strong base, strong nucleophile 3° reaction will be

A

E2

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20
Q

With a weak base, strong nucleophile 1°/2° reaction will be

A

SN2

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21
Q

With a weak base, strong nucleophile 3° reaction will be

A

SN1

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22
Q

With a weak base, weak nucleophile 1°/2° reaction will be

A

no reaction!

23
Q

With a weak base, weak nucleophile 3° reaction will be

A

SN1/E2

24
Q

Aryl halide

A

connected to aromatic ring

25
Q

Vinyl halide

A

connected to sp2 hybridized C

26
Q

Allylic carbocation

A

adjacent to double bond

27
Q

why is the backside attack necessary in SN2 reactions?

A

because in the intermediate step both bonded molecules have a partial negative charge and must be 180° away from each other

28
Q

aprotic solvents

A

acetone
DMSO
DMF
Acetonitrile

29
Q
A

Acetonitrile

30
Q
A

acetone

31
Q
A

DMSO

32
Q
A

DMF

33
Q

Alkene Hydrohalogenation mechanism and product

A

2 step processes
HX used as reagent
1. Pi bond acts as nucleophile, and grabs H
2. Most stable carbocation is made
3. X takes electrons
4. X- acts as nucleophile and attacks carbocation in Markovnikov fashion
Forms alkyl halide, enantiomers can form if a new chiral center is formed,

34
Q

Alkene Hydrohalogenation with ROOR product

A

Anti-markovnikov product because no carbocation is formed

35
Q

Why can chirality happen when there is a carbocation intermediate?

A

because attack can come from either side

36
Q

When you see a change in constitutional structure, what has likely occurred?

A

carbocation rearrangement

37
Q

Alkene Acid Catalyzed Hydration Mechanism and Product

A

Requires addition of a strong (non halogen) acid
Protonated water (hydronium) acts as electrophile
1. Pi bond grabs H
2. Carbocation is formed (can rearrange)
3. Water gains electrons
4. Water acts as nucleophile in Markovnikov fashion and attacks carbocation form oxonium ion
5. water picks up H to restore hydronium ion and neutralize + charge
Forms alcohol, check for stereochemistry/enantiomers

38
Q

Alkene Hydroboration-oxidation reagents and products

A

Reagents: 1) BH3, THF 2) H2O2, NaOH
BH3 blocks Markovnikov addition, proceeds as anti-Markovnikov
H and OH follow syn addition or are cis to each other (trans from any existing substituents on double bond)
Products can be enantiomers or diastereomers

39
Q

Hydroboration-oxidation product for an E or Z alkene

A

E alkene: syn addition gives RS configuration
Z alkene: syn addition gives RR or SS configuration

40
Q

When to use Hydroboration-oxidation?

A

when you specifically want the anti-markovnikov product of an asymmetrical alkene
when you want to avoid rearrangement

41
Q

Alkene Hydrogenation reagents and products

A

Reagents: H2 and inert metal (Pt)
H add to metal and stabilize alkene
Syn addition of 2 H
Can create meso compounds for symmetrical alkenes

42
Q

Alkene Halohydrin formation reagents and products and mechanism

A

Reagents: X2 and water as solvent
X2 separates, X- nucleophilic attack on the alkene forming a X tent
Water acts as second nucleophile forming trans OH-X product on adjacent carbons
Water picks up H from OH substituent
Forms enantiomers

43
Q

Alkene Halohydrin formation for a non-symmetric alkene

A

Markovnikovian - halide goes to the less substituted carbon, OH goes to more substituted

44
Q

Alkene Oxidative cleavage reagents and products

A

Reagents: O3 and DMS
each carbon in the double bond forms an oxygen double bond (is oxidized)
No E/Z considerations

45
Q

Acid-Base Alkyne (Carbon Chain Extension) reagents, products and mechanism

A

Reagents: 1) NaNH2 2) R-X
Strong base used to deprotonate acetylene into alkynide ion
Alkynide ion acts as strong nucleophile for SN2 to form a longer alkyne
No 3° halides can be used
Can be done for both H of acetylene

46
Q

Alkyne Preparation reagents and products

A

Reagents: 1) xs NaNH2/NH3 2) H2O
xs reagent to remove both X
can use germinal (same C) or vicinol (adjacent C) halides
E2 reaction x 2

47
Q

Hydrogenation of Alkynes reagents and products

A

Reagents: xs H2 with Pd/Pt inert metal to form alkane
To form cis alkene use Lindlar’s catalyst
To form trans alkene use Na (s) and NH3 (l)

48
Q

Hydrohalogenation reagents, products and mechanism

A

Reagents Markovnikov: xs HX
1 mol HX to stop at alkene
Reagents Anti-Markovnikov: xs HX and ROOR
Pi bond attacks H forming carbocation, X accepts electrons
X does nucleophilic attack on carbocation

49
Q

Reverse hydrohalogenation is

A

alkyne preparation using xs NaNH2/NH3 and H2O

50
Q

Hydration of Terminal Alkynes reagents and products

A

Reagents: H2SO4, H2O and HgSO4
From a terminal alkene forms enol intermediate R-C(OH)=C
and then forms ketone only
AKA acid tautomerization

51
Q

Hydroboration of Terminal Alkynes reagents and products

A

Reagents: 1) R2BH 2) H2O2, NaOH
Products: forms aldehyde only
R2BH = disiamylborane

52
Q

Halogenation of Alkynes reagents and products

A

1 mol X2 produces trans vicinal dilhalide (major product) and cis vicinal dihalide (minor product)
xs X2 –> tetrahalide

53
Q

Ozonolysis of alkynes reagents and products

A

Reagents: 1) O3 2) H2O
Produces carboxylic acids R-C(OH)=O

Organic Chemistry (4 decks)

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