Chapter 7 Flashcards
(75 cards)
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)
2
Q
T/F
Alkyl halides are polar and have dipole dipole forces.
A
True
3
Q
Methyl halide?
A
CH3X
4
Q
1 alkyl halide?
A
RCH2X
5
Q
2 alkyl halide?
A
RRCHX
6
Q
3 alkyl halide?
A
RRRCX
7
Q
What factors lead to a higher melting/boiling point?
A
- larger surface area
- more polarizable halogen
8
Q
Which atom is more polarizable, F or I?
A
Iodine, charge can spread out more
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
10
Q
Why are alkyl halides good solvents?
A
weakly polar
11
Q
What is Acutumine?
A
- produced from hanging vine
- can use it as analgesic, antipyretic
12
Q
What is Freon 11?
A
CFCl3, used for refrigeration
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
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
15
Q
What is used instead of Freon 11 now?
A
HFCs or HCFCs- destroyed before they reach ozone, less efficient
16
Q
What is DDT?
A
-insecticide-kills bugs (malaria, typhus)
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
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
19
Q
What is substitution?
A
Nucleophile replaces halide
20
Q
What are examples of good leaving groups?
A
Cl, Br, I, OH2+, N2+, OTs
21
Q
What are some characteristics of Nucs?
A
- negatively charged
- salts (NaOH)
22
Q
What is needed for a neutral Nuc to substitute?
A
excess is needed
23
Q
Good LGs are inversely correlates with _______.
A
basicity
-weaker base is better LG
24
Q
Why cant OH be a LG?
A
too strong of a base
25
Going across the PT, basicity _______.
decreases
26
Going down the PT, basicity _______.
decreases, better LGs
27
What does pKa tell you about LGs?
- if less than 0, good LG
| - CB of strong acids are good LGs
28
Basicity?
- related to Eq constant
- thermodynamics property
- high pKa, low Ka
29
Nucleophilicity?
- kinetic property
- how fast does it go
- good Nuc= rapid rate
30
If Nuc atoms are identical, stronger Nuc is the ______.
stronger base
31
Negatively charged Nuc will always be stronger than its _____.
CA
32
Across PT, Nuc will always _____ with basicity.
correlate
33
NH2 vs OH, better Nuc?
NH2 is stronger base
34
When is Nuc and Basicity not correlated?
when there is a bulky group, it is slower, not a good Nuc, steric hindrance
35
Steric hindrance?
decrease in reactivity due to presence of bulky groups
36
Going down PT, what is most solvated?
F most
| I least
37
Higher solvated = ______ Nucleophilicity.
decreased
38
In polar protic solvents, going down PT, Nucleophilicity _______.
increases
| -I is better than F
39
What happens in polar protic as opposed to polar aprotic solvents?
- protic- both cation and anion are solvated
| - aprotic- only cation is solvated
40
what are some examples of polar aprotic solvents?
```
acetone
DMSO
Ethers
THF
DMF
CH3CN
acetonitrile
```
41
In polar aprotic solvents, going down PT, Nucleophilicity ______.
decreases
- F is better than I
- correlates with basicity
42
Usually the stronger base is a better Nuc, what are two exceptions?
1. steric hindrance
2. polar protic solvents
Negative Nuc= strong
Neutral Nuc= NH3 is strong
43
A concerted substn is _____ order kinetics.
2nd
| -one step
44
What is the rate law for concerted substn?
rate = k[Nuc][C-X]
45
A stepwise substn is ______ order kinetics.
1st
| -two step (endo)
46
What is the rate law for stepwise substn?
rate = k[C-X]
47
Sn2 is a _____ mechanism.
concerted, bimolecular, 2nd order
48
Sn1 is a ____ mechanism.
stepwise, unimolecular, 1st order, only depends on reactants
49
Which mechanism has inverted configuration of products? why?
- Sn2
| - backside attack
50
How does rate correlate with Me, 1, 2, 3 alkyl halides in Sn2?
Me is the fastest, 3 is essentially unreactive b/c of increasing Ea
rates are proportional to Ea
51
In Sn2, when steric hindrance increases, reactivity ______.
decreases
52
What are two important Sn2 reactions?
- Myambutol- TB drug
| - Prozac
53
What is good to use in the lab for Sn2 reactions? why? is it good for the body?
CH3I
- I is good LG
- not good for body, not soluble, toxic
54
What is good in for the body for Sn2 reactions?
SAM
- whole thing is LG except CH3
- good LG, weak base, +sulfur
- building block for protein, DNA
- good for adrenaline synthesis
55
What type of reaction is mustard gas? why is it bad for body?
- Sn2
- Nuc and Electro in same molecule
- your DNA attacks sulfur
- causes crosslinks in DNA
- temporary blindness (Hitler, WW1)
56
What did Lt. Col. Alexander find out about Mustard Gas?
- 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
In Sn1, rate doesnt include ______.
Nucleophile
58
What type of intermediate is created in Sn1?
carbocation
59
Characteristics of carbocation intermediates?
- high energy intermediates
- never isolated
- form slowly, react quickly, consumed fast
60
What is the stereochem of Sn1 rxns?
racemic mix of products 1:1
61
Why is Sn1 racemic?
achiral carbocation intermediate that can be attacked equally from both sides
62
Solvolysis?
solvent is Nuc in substn
63
What type of geometry does the carbocation intermediate have in Sn1?
trigonal planar
64
How does rate correlate with Me, 1, 2, 3 alkyl halides in Sn1?
3 is the fastest, Me is the slowest
| -opposite trend of Sn2
65
Generally which mechanism is slower, Sn1 or Sn2?
Sn1
66
Carbocation stability?
3>2>1>Me
67
There is a stronger inductive effect the more ____ groups are attached to a C.
R
68
Stronger inductive effect = ______ _______. Why?
carbocation stability
| -electrons are donated to center, able to spread out positive charge with more R groups
69
Hyperconjugation?
- spreading out charge by overlap of an empty P orbital with adjacent sigma bond
- more stable
70
Hammonds Postulate?
- 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
More stable carbocation always forms ______.
faster
72
What is an important Sn1 reaction?
spam
- NaNO2- preservative, kills botulism, can react with amines in body to generated carbocations in Sn1 rxns, causes cancer
- benefits outweigh risks
73
Polar protic solvent favors _____.
Sn1
74
Polar aprotic solvent favors _____.
Sn2
| -Nuc not solvated
75
Why doesnt vinyl halide undergo substn?
- sp2 hybridized
| - carbocation highly unstable
