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Organic Chemistry I > CHP 10 - 11 > Flashcards

CHP 10 - 11 Flashcards

1
Q

What are the 3 steps in radical chain rxn mechanisms?

A
  1. Initiate
  2. Propagation (rxn)
  3. Terminate (radicals go away)
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2
Q

What happens in the initiation step of a radical chain mechanism?

A

homolysis

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3
Q

What happens in the propagation step of a radical chain mechanism?

A

Product always ends up in propagation step

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4
Q

What happens in the termination step of a radical chain mechanism?

A

The radicals (terminate) go away

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5
Q

What is Heterolysis?

A

The movement of 2 full electrons

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6
Q

What is homolysis?

A

The movement of 1 electron at a time. Energy introduced into the system to create a radical. AKA homolytic bond cleavage when the bond breaks, each atom will add 1 electron.

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7
Q

Name this overall reaction

A

Reaction of Radical: Halogenation of Alkanes

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8
Q

Why is there selectivity (differenced in reactivity) between Br and Cl?

A

Reaction Kinetics.
The rxn of Cl2 has exothermic intermediates
The rxn of Br2 has endothermic intermediates

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9
Q

How to predict the major product of the following reaction

A
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10
Q

What is N-bromosuccinimide (NBS) and N-chlorosuccinimideused (NBS) for?

A

NBS and NCS are specifically used for brominating and chloronating allylic/benzylic positions

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11
Q

What radical initiators can be used with NBS?

A

peroxides ROOR

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12
Q

Name this overall reaction

A

Halogenation at the allylic/benzylic position

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13
Q

Name this overall transformation

A

Addition of radicals to Alkenes

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14
Q

Properties of Addition of radicals to Alkenes

A
  1. Anti-Markov addition of H-Br
    1. Radicals do not rearrange ( remember carbocations do rearrange)
    2. Reaction does not work w/ HI or HCl
      Stereochemistry (50/50 mixture)
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15
Q

What is the initiation step of the radical chain reaction mechanism for Addition of radicals to Alkenes?

A
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16
Q

What is the propagation step of the radical chain reaction mechanism for Addition of radicals to Alkenes?

A
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17
Q

What is the termination step of the radical chain reaction mechanism for Addition of radicals to Alkenes?

A
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18
Q

What are the following examples?

A

Examples of stereochemistry in Addition of Radicals to Alkene mechanisms

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19
Q

Solve this Addition of Radicals to Alkenes synthesis

A

What’s changed? New C-C bond

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20
Q

What are the two organometallic compounds to know for this class?

A

organolithium (R-Li) and Grignard organomagnesium (RMgBr)

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21
Q

What is the reactivity of R-Li and RmgBr?

A

Carboanion Reactivity:
1. Very strong base
2. Strong nucleophile

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22
Q

Name this organometallic mechanism

A

R-Li
Conjugate acid is a stronger acid because pka is greater that 8 points so the rxn is R->P irreversible

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23
Q

Name this organometallic mechanism

A

RMgBr Grinard

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24
Q

What type of solvents should be used for R-Li and RMgBr reactions?

A

Anhydrous or “dry” solvents such as Et2O to avoid H2O ruining the reaction

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25
Q

How does RMgBr react with epoxides?

A

RMgBr acts as a strong nucleophile (base)

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26
Q

What are the two main coupling reactions that we are learning?

A

Gilman- Organocuprates (CuLi) and Suzuki-Miyaura Reaction (B(OH)2 and Pd(0))

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27
Q

Name this coupling mechanism

A

Organocuprates
Gilman Reagent + alkyl halide=stitched compound

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28
Q

Name this coupling mechanism

A

Organocuprates
Gilman Reagent + alkyl halide=stitched compound

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29
Q

Name this coupling mechanism

A

Suzuki-Miyaura Reaction (B(OH)2 and Pd(0))

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30
Q

What type of reaction with B(OH)2 and Pd(0) always make?

A

coupling reaction

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31
Q

What does this overall transformation represent?

A

General scheme for substitution nucleophilic 2nd order biomolecular (SN2) reactions. The overall reaction is in 2nd order and rate=k[Nu][R-L.G]

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32
Q

What does this overall transformation represent?

A

General scheme for substitution nucleophilic 2nd order biomolecular (SN2) reactions. The overall reaction is in 2nd order and rate=k[Nu][R-L.G]

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33
Q

Name this mechanism

A

SN2 mechanism

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34
Q

In SN2 reactions, how does attacking the backside of a leaving group change the stereochemistry?

A

We get an inversion of stereochemistry a the carbon

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35
Q

What does the rate of SN2 reactions depend on?

A

The class of L.G, sterics of beta carbon (carbon right next to the carbon with the alkyl halide), and L.G. ability to leave (weaker the better)
methyl» 1 > 2&raquo_space; 3 (tertiary cannot happen)

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36
Q

What is the rate of leaving trend for L.G. in a SN2 rxn?

37
Q

Define Nucleophiles

A

Nucleophiles (electron rich substance that want to share electrons with a nucleus) are electron pair donors (Lewis base) and react with a nucleus (carbon nucleus)

38
Q

Define Electrophile

A

Electrophile (electron deficient willing to accept electrons) is an electron pair acceptor (Lewis acid)

39
Q

Define Leaving groups (L.G)

A

Leaving groups (L.G): typically stable ions or neutral species when they leave. Conjugate bases of strong acids (pKa<5)

40
Q

Strong nucleophiles go SN2. Compounds with negative charges are more nucleophilic than neutral species because

A

they want to share electrons to relieve the negative charge.

41
Q

pKa of alcohols

42
Q

pKa of phenols

43
Q

pKa of carboxylic acids

44
Q

Polar Aprotic solvents used in SN2 reactions where strongest base = strongest Nu

A

DMSO
DMF
DMA
HMPA
acetone
THF

If the solvent is polar aprotic then it is SN2 because we can dissolve the SM, stabilizes the charge better, and stabilizes the TS.

45
Q

Polar Protic solvents used in SN1, E2, and E1 reactions where the strongest base = weakest Nu

A

H2O
EtOH, MeOH
NH3
AcOH

46
Q

How are nucleophiles affected by sterics?

A

More sterics = bad nucleophile
Less sterics = good nucleophile

47
Q

Predict the product and state whether this is SN1, SN2, E1, or E2

48
Q

Predict the product and state whether this is SN1, SN2, E1, or E2

49
Q

Predict the product and state whether this is SN1, SN2, E1, or E2

50
Q

Predict the product and state whether this is SN1, SN2, E1, or E2

51
Q

How many steps are in SN1?

52
Q

Name the reaction of this general scheme

53
Q

Show the mechanism for this SN1 reaction

54
Q

What is the rate trend of the L.G. class in SN1 reactions?

55
Q

What is the pKa L.G. trend for SN1?

56
Q

Predict the product of this SN1 reaction

57
Q

Predict the product of this SN1 reaction

58
Q

Predict the product of this SN1 reaction

59
Q

Predict the product of this SN1 reaction

60
Q

Predict the product of this SN2 reaction

61
Q

Predict the product of this SN1 reaction

62
Q

Predict the product of this SN2 reaction

63
Q

Predict the product of this SN1 reaction

64
Q

What is Zaitsev’s rule and when is it used?

A

The major product is the more substituted/stable product. Used in E2 reactions

65
Q

What are the exceptions to Zaitsev’s Rule?

A

All follow Hoffman’s which is anti=Zaitsev
Conjugated Alkenes
Big Bulky Bases
Fluorine L.G.

66
Q

Predict the product of the following E2 reaction

67
Q

Predict the product of the following E2 reaction

68
Q

Predict the product of the following E2 reaction

69
Q

Predict the product of the following E2 reaction

70
Q

Predict the product of the following E2 reaction

71
Q

Predict the product of the following E2 reaction

72
Q

Predict the product of the following E2 reaction

73
Q

What are the rates of leaving groups I, Br, Cl, F in E2 reactions?

74
Q

Strong charged bases such as NaOH, KOH, NaOCH3 and KOEt can do both SN2 and E2 rxns. How do we determine which way the rxn will go?

A

pKa values and the class of L.G.
When pKa > 11 then E2 because basic
When pKa < 11 then SN2 because nucleophilic

75
Q

Write the mechanism for the following E1 rxn

76
Q

Does heat favor E1 or SN1? Do warm conditions favor E1 or SN1?

A

Heat favors E1 and warm conditions favor SN1

77
Q

How many steps are there in E1 rxns?

78
Q

What reaction is described below?
Properties:
1. Rate depends on formation of carbocation. 3 > 2 >(1 does not form)
2. The alkene formed is on the most substituted and thermodynamically stable carbon
3. Mechanism has rearrangments
4. Rate of L.G. = I > Br > Cl > (F does not form) and H2O (dehydration)

79
Q

Write the mechanism for the following E1 reaction

80
Q

Write the mechanism for the following E1 reaction

81
Q

Predict the product of the following rxn

82
Q

Predict the product of the following rxn

83
Q

Predict the product of the following rxn

84
Q

Predict the product of the following rxn

85
Q

Complete this radical halogenation mechanism

86
Q

Complete this Gilman reaction

87
Q

Why would concentrated HBr be an inappropriate catalyst for the dehydration of alcohols?

A

The conjugate base Br is a good nucleophile and it would attack the carbocation to form an alkyl bromide.

88
Q

What would be the first step in the dehydration of cyclohexanol in sulfuric acid?

A

protonation of the alcohol

89
Q

What time of reaction is a one step process with inversion of configuration?

Organic Chemistry I (12 decks)

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