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Chem 351 > Chapter 7 > Flashcards

Chapter 7 Flashcards

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1
Q

What types of halides do not undergo nucleophilic substitution?

A

vinyl (halide attached to double bond)

aryl (halide attached to double bond in ring)

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2
Q

T/F

Alkyl halides are polar and have dipole dipole forces.

A

True

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3
Q

Methyl halide?

A

CH3X

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4
Q

1 alkyl halide?

A

RCH2X

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5
Q

2 alkyl halide?

A

RRCHX

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6
Q

3 alkyl halide?

A

RRRCX

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7
Q

What factors lead to a higher melting/boiling point?

A
  • larger surface area

- more polarizable halogen

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8
Q

Which atom is more polarizable, F or I?

A

Iodine, charge can spread out more

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9
Q

Why doesnt food stick to teflon?

A
  • repeating chain of F’s
  • not very polarizable
  • high electroneg pulls electrons tight
  • F doesnt interact with other molecules
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10
Q

Why are alkyl halides good solvents?

A

weakly polar

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11
Q

What is Acutumine?

A
  • produced from hanging vine

- can use it as analgesic, antipyretic

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12
Q

What is Freon 11?

A

CFCl3, used for refrigeration

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13
Q

Why is Freon 11 good for fridges?

A
  • very easily vaporized, absorbs heat, thats how it cools fridge
  • nonflammable
  • also used as a propellant for aerosol cans
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14
Q

What is the problem with Freon 11?

A
  • degrades ozone layer
  • stable enough to make it to upper atmosphere
  • gives off Cl- atoms which destructures ozone

-ozone converts UV light to heat, protects against skin cancer

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15
Q

What is used instead of Freon 11 now?

A

HFCs or HCFCs- destroyed before they reach ozone, less efficient

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16
Q

What is DDT?

A

-insecticide-kills bugs (malaria, typhus)

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17
Q

What is the problem with DDT?

A
  • not water soluble
  • moves up food chain, cannot excrete
  • not harmful to humans
  • makes birds egg shells very thin, kills them
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18
Q

What are some properties of alkyl halides?

A
  • polar bond between C and halogen group
  • partial + on C, partial - on halo
  • lewis basic on halo
  • electrophilic C dominates reactivity
  • electrons always go to halo
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19
Q

What is substitution?

A

Nucleophile replaces halide

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20
Q

What are examples of good leaving groups?

A

Cl, Br, I, OH2+, N2+, OTs

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21
Q

What are some characteristics of Nucs?

A
  • negatively charged

- salts (NaOH)

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22
Q

What is needed for a neutral Nuc to substitute?

A

excess is needed

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23
Q

Good LGs are inversely correlates with _______.

A

basicity

-weaker base is better LG

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24
Q

Why cant OH be a LG?

A

too strong of a base

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25
Q

Going across the PT, basicity _______.

A

decreases

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26
Q

Going down the PT, basicity _______.

A

decreases, better LGs

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27
Q

What does pKa tell you about LGs?

A
  • if less than 0, good LG

- CB of strong acids are good LGs

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28
Q

Basicity?

A
  • related to Eq constant
  • thermodynamics property
  • high pKa, low Ka
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29
Q

Nucleophilicity?

A
  • kinetic property
  • how fast does it go
  • good Nuc= rapid rate
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30
Q

If Nuc atoms are identical, stronger Nuc is the ______.

A

stronger base

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31
Q

Negatively charged Nuc will always be stronger than its _____.

A

CA

32
Q

Across PT, Nuc will always _____ with basicity.

A

correlate

33
Q

NH2 vs OH, better Nuc?

A

NH2 is stronger base

34
Q

When is Nuc and Basicity not correlated?

A

when there is a bulky group, it is slower, not a good Nuc, steric hindrance

35
Q

Steric hindrance?

A

decrease in reactivity due to presence of bulky groups

36
Q

Going down PT, what is most solvated?

A

F most

I least

37
Q

Higher solvated = ______ Nucleophilicity.

A

decreased

38
Q

In polar protic solvents, going down PT, Nucleophilicity _______.

A

increases

-I is better than F

39
Q

What happens in polar protic as opposed to polar aprotic solvents?

A
  • protic- both cation and anion are solvated

- aprotic- only cation is solvated

40
Q

what are some examples of polar aprotic solvents?

A 
acetone
DMSO
Ethers
THF
DMF
CH3CN
acetonitrile
41
Q

In polar aprotic solvents, going down PT, Nucleophilicity ______.

A

decreases

  • F is better than I
  • correlates with basicity
42
Q

Usually the stronger base is a better Nuc, what are two exceptions?

A
  1. steric hindrance
  2. polar protic solvents

Negative Nuc= strong
Neutral Nuc= NH3 is strong

43
Q

A concerted substn is _____ order kinetics.

A

2nd

-one step

44
Q

What is the rate law for concerted substn?

A

rate = k[Nuc][C-X]

45
Q

A stepwise substn is ______ order kinetics.

A

1st

-two step (endo)

46
Q

What is the rate law for stepwise substn?

A

rate = k[C-X]

47
Q

Sn2 is a _____ mechanism.

A

concerted, bimolecular, 2nd order

48
Q

Sn1 is a ____ mechanism.

A

stepwise, unimolecular, 1st order, only depends on reactants

49
Q

Which mechanism has inverted configuration of products? why?

A
  • Sn2

- backside attack

50
Q

How does rate correlate with Me, 1, 2, 3 alkyl halides in Sn2?

A

Me is the fastest, 3 is essentially unreactive b/c of increasing Ea

rates are proportional to Ea

51
Q

In Sn2, when steric hindrance increases, reactivity ______.

A

decreases

52
Q

What are two important Sn2 reactions?

A
  • Myambutol- TB drug

- Prozac

53
Q

What is good to use in the lab for Sn2 reactions? why? is it good for the body?

A

CH3I

  • I is good LG
  • not good for body, not soluble, toxic
54
Q

What is good in for the body for Sn2 reactions?

A

SAM

  • whole thing is LG except CH3
  • good LG, weak base, +sulfur
  • building block for protein, DNA
  • good for adrenaline synthesis
55
Q

What type of reaction is mustard gas? why is it bad for body?

A
  • Sn2
  • Nuc and Electro in same molecule
  • your DNA attacks sulfur
  • causes crosslinks in DNA
  • temporary blindness (Hitler, WW1)
56
Q

What did Lt. Col. Alexander find out about Mustard Gas?

A
  • kills WBC’s which divide rapidly
  • might kill cancer
  • Goodman/Gilman- created Mustargen which was the first anticancer drug
  • Cytoxan- less side effects than Mustargen
57
Q

In Sn1, rate doesnt include ______.

A

Nucleophile

58
Q

What type of intermediate is created in Sn1?

A

carbocation

59
Q

Characteristics of carbocation intermediates?

A
  • high energy intermediates
  • never isolated
  • form slowly, react quickly, consumed fast
60
Q

What is the stereochem of Sn1 rxns?

A

racemic mix of products 1:1

61
Q

Why is Sn1 racemic?

A

achiral carbocation intermediate that can be attacked equally from both sides

62
Q

Solvolysis?

A

solvent is Nuc in substn

63
Q

What type of geometry does the carbocation intermediate have in Sn1?

A

trigonal planar

64
Q

How does rate correlate with Me, 1, 2, 3 alkyl halides in Sn1?

A

3 is the fastest, Me is the slowest

-opposite trend of Sn2

65
Q

Generally which mechanism is slower, Sn1 or Sn2?

A

Sn1

66
Q

Carbocation stability?

A

3>2>1>Me

67
Q

There is a stronger inductive effect the more ____ groups are attached to a C.

A

R

68
Q

Stronger inductive effect = ______ _______. Why?

A

carbocation stability

-electrons are donated to center, able to spread out positive charge with more R groups

69
Q

Hyperconjugation?

A
  • spreading out charge by overlap of an empty P orbital with adjacent sigma bond
  • more stable
70
Q

Hammonds Postulate?

A
  • The transition state of reaction resembles the structure to which it is closest in energy
  • more stable forms faster
  • if rxn is endo, transition state resembles products
  • doesnt explain exo
71
Q

More stable carbocation always forms ______.

A

faster

72
Q

What is an important Sn1 reaction?

A

spam

  • NaNO2- preservative, kills botulism, can react with amines in body to generated carbocations in Sn1 rxns, causes cancer
  • benefits outweigh risks
73
Q

Polar protic solvent favors _____.

A

Sn1

74
Q

Polar aprotic solvent favors _____.

A

Sn2

-Nuc not solvated

75
Q

Why doesnt vinyl halide undergo substn?

A
  • sp2 hybridized

- carbocation highly unstable

Chem 351 (5 decks)

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