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CHM 241 Dr. Erb > Final Exam > Flashcards

Final Exam Flashcards

1
Q

sulfonates

A
  • So3 groups
  • S is double bonded to two oxygens and single bonded to the third oxygen
  • very good leaving groups because of resonance
  • made from corresponding alcohol in a reaction
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2
Q

alcohols in elimination and substitution reactions

A

they are bad leaving groups so they get converted into good leaving groups by sulfonates or strong acids

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3
Q

-OH as a reagent

A

strong nucleophile and a strong base

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4
Q

pyridine

A

non-nucleophilic base

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5
Q

how is the alpha carbon respresented in sulfonate reactions?

A

with R

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6
Q

stereochemistry of OH and sulfonate reactions

A

stereochemistry does not change because the sulfur gets attacked

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7
Q

how are alcohols used as starting materials in reactions?

A

to make alkyl halides and alkenes

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8
Q

What needs to occur if an alcohol is the reactant?

A

strongly acidic conditions are needed to protonate OH into H2O because H2O is a good leaving group

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9
Q

HBr as a reagent

A

strong acid, not a nucleophile or base

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10
Q

Br as a reagent

A

strong nucleophile only, encourages substitution

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11
Q

HX mechanism for alcohols

A
  • results in a substitution reaction
  • primary alcohols react Sn2
  • secondary and tertiary alcohols react Sn1
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12
Q

what conditions are protic conditions?

A

strongly acidic

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13
Q

elimination of alcohols

A

-favored by H2SO4 because the byproduct of the first step
-favored by heat
-

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14
Q

what do protic conditions favor?

A

E1 for secondary and tertiary substrates

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15
Q

retrosynthesis

A

thinking and synthesizing backwards

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16
Q

addition reactions

A
  • opposite of elimination reactions
  • pi bonds act as lewis bases, nucleophiles or bronsted lowry bases
  • at temperature dependent equilibrium with elimination reactions
  • typically add 2 atoms across a pi bond
  • usually exothermic
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17
Q

what does 🔼G represent in elimination reactions?

A

competition between the enthalpy and entropy term

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18
Q

low temperature 🔼G reactions

A
  • entropy is small
  • enthalpy dominates
    • 🔼G
  • K>1
  • products favored
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19
Q

high temperature 🔼G reactions

A
  • entropy is large
  • entropy dominates
  • +🔼G
  • K<1
  • reactants favored
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20
Q

why are addition reactions usually exothermic?

A

a pi bond is broken and 2 sigma bonds are formed

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21
Q

enthalpy for exothermic addition reactions

A

neagtive

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22
Q

entropy of addition reactions

A

entropically unfavorable(- 🔼S) because 2 molecules become one

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23
Q

how can an addition reaction be favorable if the entropy is unfavorable?

A

enthalpy magnitude outweighs unfavorable affect of enthalpy

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24
Q

which types of addition reactions are most closely related?

A

halogenation and halohydrin formation

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25
Q

hydrohalogenation

A

a reaction where H and a halide are added across a pi bond

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26
Q

hydrohalogenation mechanism

A
  1. Proton transfer generates a carbocation

2. nucleophilic attack

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27
Q

rate determining step of hydrohalogenation reactions

A

proton transfer/carbocation generation step(the first step)

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28
Q

function of an alkene in hydrohalogenation

A

alkenes function as a base

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29
Q

how are alkenes able to function as bases if they arent basic?

A

in hydrohalogenation, the acid is so strong that the alkene can play the basic role

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30
Q

characteristics of carbocation intermediate in hydrohalogenation

A
  • flat
  • can be attack fromt he top or bottom
  • strong electrophile
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31
Q

Markovnikov’s rule

A

H is added to the vinylic C atom bearing more H atoms, or the less substituted carbon

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32
Q

regiochemistry of hydrohalogenation reactions

A

pro-markovnikov rule

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33
Q

why is markovnikov’s rule usually executed in addition reactions?

A

it creates the most stable possible carbocation, which stabilizes the transition state and allowing the product to form faster

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34
Q

What decides the activation energy of a reaction?

A

the transition state energy level

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35
Q

What stabilizes the carbocation intermediate in addition reactions?

A

hyperconjugation from the more substituted atom

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36
Q

When does hydrohalogenation result in a racemic mixture?

A

When a chiral center forms

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37
Q

What decides the regio and stereo chemistry of addition reactions?

A

the formation of the carbocation

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38
Q

methods of alkene hydration

A
  1. Acid catalyzed hydration
  2. Oxymercuration-demurcation
  3. Hydroboration-oxidation
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39
Q

acid-catalyzed hydration regiochemistry

A

markovnikov addition

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40
Q

stereochemistry of acid catalyzed reactions

A

racemic mixture of products

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41
Q

are rearrangements possible for hydrohalogenation?

A

yes

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42
Q

are rearrangments possible for acid catalyzed hydration?

A

yes

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43
Q

regiochemistry of oxymerucration-demercuration

A

markovnikov addition

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44
Q

stereochemistry of oxymercuration-demercuration

A

anti addition

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45
Q

are rearrangements possible in oxymercuration-demercuration reactions?

A

no

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46
Q

regiochemistry of hydroboration-oxidation reactions

A

anti-markovnikov

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47
Q

stereochemistry of hydroboration-oxidation reactions?

A

syn addition

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48
Q

are rearrangements possible for hydroboration-oxidation reactions?

A

no

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49
Q

What do acid catalyzed reactions do to a molecule?

A

add H2O to a bond by adding H to one side and OH to the other

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50
Q

how is the acid catalyst shown in acid catalyzed reactions

A

it is shown over the arrow and in brackets because it is regenerated rather than being a reactant

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51
Q

what is also present when H2SO4 is an acid catalyst?

A

H3O+

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52
Q

how do we know an acid catalyzed hydration has carbocation intermediates?

A

OH is added to the more substituted carbon of the alkene

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53
Q

Acid catalyzed hydration mechanism

A
  1. Proton transfer: alkene is protonated and carbocation intermediate is formed
  2. Nucleophilic attack: water functions as a nucleophile to attack the carbocation intermediate
  3. Proton transfer: water functions as a base to deprotonate the oxonium ion and give the product
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54
Q

purpose of the last proton transfer in acid catalyzed reactions

A

O+ is very unstable and is never the final product

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55
Q

what determines the rate of addition reactions with rearrangement?

A

carbocation stability

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56
Q

thermodynamics of acid catalyzed reaction

A

at equilibrium between alkene and addition product

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57
Q

what type of addition reaction do acid catalyzed reactions have the same thermodynamics as?

A

hydrohalogenation reactions

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58
Q

How can equilibrium be pushed toward addition products and away from alkenes in acid catalyzed hydration?

A
  1. Low temp: with a small entropy, enthalpy will dominate and a low temp will make △G negative
  2. Use dilute H2SO4 and a lot of water: this utilizes LeChatelier’s principle because water is on the elimination side of the reaction
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59
Q

why do acid catalyzed reactions produce racemic mixtures?

A

their carbocations are trigonal planar and therefore flat

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60
Q

what limits synthetic utility of Markovnikov reactions?

A

rearrangements produce a mixture of products

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61
Q

what is a solution to the limited synthetic ability of markovnikov reactions?

A

oxymercuration-demercuration reactions, no rearrangements

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62
Q

Oxymercuration-demercuration mechanism

A

Part 1-Oxymercuration
1. dissociation of mercuric acetate forming a mercuric cation: OAc leaves Hg+-OAc

  1. Pi bond attacks Hg+ forming two resonance structures(one with and one without a ring) as intermediates.

Part 2-Demercuration
3. NaBH4 replaces and reduces the HgoAc group

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63
Q

what role does a mercuric cation play oxymercuration-demercuration reactions?

A

it is an electrophile that gets attacked by a nucleophile(the alkene)

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64
Q

why don’t oxymercuration-demercuration reactions have carbocation intermediates?

A

in the mechanism, the resulting intermediate is not a carbocation because mercury has electrons that can interact with the nearby positive charge to form a bridge

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65
Q

oxymercuration-demercuration intermediate

A

2 resonance structures: one with and one without a ring. The lone pairs and + charge switch places in the resonance

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66
Q

Why don’t oxymercuration-demercuration reactions undergo carbocation rearrangments?

A

The more substituted carbon bears a partial positive charge instead of a full positive charge

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67
Q

types of stereochem in addition reactions

A
  1. Anti-addition: Nucleophile is added to the opposite side of the other added group
  2. Syn-addition: Added groups are added to the same side
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68
Q

What causes oxymercuration-demercuration reactions to undergo markovnikov addition?

A

the nucleophile is attracted to the more substituted side, resulting in a smaller activation energy barrier and a faster reaction due to the partial positive charge where the nucleophile is added

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69
Q

What happens to an oxymercuration-demercuration rings as a nucleophile gets close?

A

it opens up

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70
Q

Purpose of NaBH4 in oxymercuration-demercuration reactions

A

replace and reduce the HgOAc groups with a -H groups via a free radical mechanism, maintaining the stereochem of the starting molecule

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71
Q

which step of oxymercuration-demercuration governs the products?

A

oxymercuration

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72
Q

Which reaction is used to achieve anti-Markovnikov hydration?

A

hydroboration-oxidation

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73
Q

Hydroboration-Oxidation mechanism

A
  1. Hydroboration: Boron is added to the less substituted carbon
  2. Oxidation: OH replaces B H2
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74
Q

Similarities and differences between BH3 and a carbocation

A

Similar because they are both reactive, both BH3 is not asn reactive because it does not carry a formal charge

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75
Q

What process do BH3 molecules undergo and why?

A

intermolecular resonance to help fulfill their octets, since they have a broken octet. This results ins hybrid B2H6

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76
Q

Bonds in B2H6

A
  • different from bonding in BH3

- bonds are called banana bonds

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77
Q

purpose of THF

A

stabilize borane(BH3) in hydroboration-oxidation reactions

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78
Q

What is responsible for the anti-mark property of hydroboration-oxidation reactions?

A

the reagent

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79
Q

reagent for hydroboration-oxidation reactions

A

BH3●THF

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80
Q

Reasons Boron is added to the less substituted carbon in hydroboration-oxidation reactions

A
  1. Electronics: since B is less electronegative than H, the partially negative H attacks the partially positive carbon which adds the H to the more subsituted alkene bond
  2. Sterics: BH2 and H are added across the double. Since BH2 is bigger, there will be less steric crowding
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81
Q

what do electronegativity differences result in?

A

dipole moments

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82
Q

intermediate for hydroboration-oxidation reactions

A

4-membered ring

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83
Q

What do 1 or 2 chiral centers result in with hydroboration-oxidation reactions?

A

racemic mixtures

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84
Q

What type of mechanism is hydroboration?

A

concerted

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85
Q

What type of addition do hydroboration-oxidation reactions?

A

syn-addition

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86
Q

catalytic hydrogenation

A

addition of H2 across a C=C bond

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87
Q

What happens if a chirality center is observed in catalytic hydrogenation?

A

syn addition

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88
Q

catalyst for catalytic hydrogenation

A

H2 with a metal catalyst

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89
Q

purpose of metal catalyst in catalytic hydrogenation reactions

A

they make the reaction work and progress at a decently fast rate and absorb H atoms

90
Q

major product of catalytic hydrogenation

A

alkane

91
Q

regiochemistry of catalytic hydrogenation

A

there is no regiochem because H is being added to both side of the pi bond

92
Q

stereochem of catalytic hydrogenation

A

syn-addition

93
Q

where is H2 added in catalytic hydrogenation and why?

A

the top or bottom bc alkenes are flat

94
Q

meso compounds

A
  • plane of symmetry

- achiral, even if chiral centers are present within the molecule

95
Q

heterogeneous catalyst

A
  • catalyst where catalysis takes place on the surface of a solid surrounded by a solution
  • does not dissolve in the reaction medium
96
Q

homogeneous catalyst

A
  • soluble in the reaction medium

- syn-addition

97
Q

halogenation

A
  • addition of two halogens across a C=C bond

- only practical addition Cl and Br

98
Q

how do Br2 and Cl2 get partial charges when they are nonpolar?

A

they are polarizable, so an induced dipole is generated when a nucleophile is nearby and Br2/Cl2 become electrophilic since electrons are repelled by the nucleophile electron density

99
Q

product of halogenation

A

alkane with the halogens on it

100
Q

regiochem of halogenation

A

no regiochem

101
Q

halogenation mechanism

A
  1. nucleophilic attack: pi bond attack Br, 3-membered ring bronomium ion forms
  2. loss of a leaving group: Br-Br bond broken
  3. nucleophilic attack: Cl/Br attacks the partially positive carbons bronium ion in an Sn2 process, Cl/Br add to the opposite side of the other Br/Cl
102
Q

how is halogenation similar to oxymercuration-demercuration?

A

they both have a 3-membered ring as a key intermediate

103
Q

stereochem of halogenation

A
  • anti because the cyclic intermediate has anti stereochem and intermediates decide the products. rings are similar in structure and reactivity
  • enantiomers are formed of the inverse stereochem doesn’t end up being identical
104
Q

why does a 3-membered ring form in halogenation?

A
  • same as Hg
  • additional lone pair
  • more stable than a carbocation bc of the partial charge compared to the full +1 charge of a carbocation
105
Q

difference between halogenation and halohydrin

A
  • the nucleophile

- solvents

106
Q

electron activity of 3-membered halogenation ring

A

electrophile

107
Q

nucleophile in halogenation

A

bromide

108
Q

halogenation

A

alkene with 2 anti Br/Cl instead of the pi bond

109
Q

solvents for halogenation

A
  • inert solvents that aren’t nucleophiles

- CH2Cl-

110
Q

halohydrin formation

A

formed when Br2/Cl2 are added to an alkene with a nucleophilic solvent(water, methanol, alcohol)

111
Q

Halohydrin mechanism

A
  1. Bronomium ion forms form Br2 + alkene
  2. ion is attacked by water
  3. proton transfer produces neutral halohydrin product
112
Q

halohydrin formation products

A

addition of -X and -OH across a C=C bond

113
Q

regiochemistry of halohydrins

A
  • regioselective because of water attacking the bromonium ion
  • OH adds to more substituted group
  • transition state with partial positive charge on Carbon that is more stable than a +1 carbocation as nucleophile gets closer
  • markovnikov addition
114
Q

regiochemistry of onzonolysis

A

no regiochemistry

115
Q

dihydroxylation

A

two -OH groups being added across a double bond

116
Q

How many steps is hihydroxylation?

A

2

117
Q

hi hydroxylation reaction intermediate

A
  • 3-membered ring with O

- allowed to fomr by O-O bond

118
Q

anti-dihydroxylation mechanism

A
  1. epoxide formed(3 membered ring with O): unstable O-O bond is replaced
  2. H is added to the epoxide O through a proton transfer
  3. nucleophilic attack of water from opposite side in an Sn2 process
  4. Proton transfer of H2O attached to ring to H2O in solution
119
Q

peroxy acid

A

have C-O-O bonds

120
Q

what is the reason for protonating the epoxide?

A

make it a stronger nucleophile so it can be attacked

121
Q

purpose of water in anti-dihydroxylation reactions

A

nucleophile

122
Q

why do anti-dihydroxylation reactions need a neutral nucleophile?

A

the product is not neutral

123
Q

what makes 3-membered ring intermediate good nucleophiles?

A

+1 formal charge and ring strain

124
Q

what products do 3-membered intermediate rings yield and why?

A

anti products because the nucleophile attacks in an Sn2 fashion

125
Q

what type of molecule is MCPBA

A

peroxyacid

126
Q

reagent of dihydroxylation reactions

A

peroxyacids followed by H3O+

127
Q

Syn-dihydroxylation mechanism

A
  1. adds across the C=C bond in one concerted step-no intermediate
  2. converts osmate ester into a diol by adding Na2SO3 or NaHSO3
128
Q

what is needed for syn dihydroxylation?

A

KMnO4 and cold temperatures

129
Q

What type of mechanism is syn-dihydroxylation?

A

concerted

130
Q

Ozonolysis process

A

ozone(O3) reacts with an alkene to form an initial primary ozonide which rearranges to a more stable ozonide. The pi bond is oxidized

131
Q

reagents in ozonolysis and their role

A
  • a mild reducing agent is used to reduce

- DMS and Zn/H2O

132
Q

how can you tell if the reactant was a ring in ozonolysis

A

if the product double bonds are on the same molecule, and there aren’t multiple molecules

133
Q

process for synthesis problelms

A
  1. determine whether the reaction is single or multi-step
  2. consider the reagents you know and which reactions might bring about the transformation
  3. determine any relevant regiochemistry and stereochemistry
  4. be as efficient as possible
134
Q

what 2 things do you look for when starting a synthesis problem?

A

whether or no the carbon skeleton changed and whether or not the functional group changed

135
Q

process for relocating a group in synthesis problems

A

eliminate then add a group

136
Q

alkynes as nucleophiles

A

similar to alkenes because of their 2 pi bonds and electron density

137
Q

types of alkynes

A
  1. terminal: useful for reactions because of their acidic H, some bases will take it
  2. Internal: sandwiched by R groups
138
Q

alkyne p orbitals

A
  • 2 p-orbitals

- 2 pi bonds, each in a different plane

139
Q

Physical properties of alkynes(goemetry and mobility)

A
  • linear
  • rigid
  • no free rotation
140
Q

alkyne naming rules

A
  1. parent chain must include C-C triple bond
  2. name subsitutents
  3. assign a locant giving the C-C triple bond the lowest number possible
  4. list numbered substituents before parent name in alphabetical order. Ignore prefixes except iso when ordering alphabetically
  5. C-C triple bond locant is plced just before the parent name or -yne
    - higher priority than alkenes
141
Q

terminal alkyne pKa and meaning

A

lower than other hydrocarbons, a strong base is needed to deprotonate it

142
Q

How can you tell if a base is strong enough to deprotonate alkynes?

A

if its conjugate acid has a higher pKa(25 for terminal alkynes)

143
Q

common bases that can deprotonate alkynes

A
  1. C-
  2. N-
  3. H-
144
Q

What mechanism can be used to prepare alkynes and why?

A

E2, they need a strong base in excess and an alkane

145
Q

what is required for E2?

A

beta H atoms

146
Q

geminal vs vicinal dihalide

A

both have 2 Cs
Geminal: 2 halides on the same Br

Vicinal: 2 Halides next to each other on different carbons

147
Q

NaNH2 strength

A

very strong base

148
Q

role of strong bases in elimination

A

shift equilibrium toward elimination products

149
Q

What is needed to acquire a neutral and charged alkyne?

A

Charged: strong base in excess
Neutral: proton transfer from proton source

150
Q

what does alkylation add?

A

addition of carbon chains

151
Q

what does hydrohalogenation of alkynes add?

A

HX

152
Q

what does hydration of alkynes add?

A

H and OH with tautomerization

153
Q

what does reduction/hydrogenation of alkynes add?

A

H atoms

154
Q

what does halogenation of alkynes add?

A

addition of excess BR2 or Cl2

155
Q

ozonolysis of alkynes reactions and results

A

reaction of ozone and water for carboxylic acids

156
Q

What is required to convert a terminal alkyne to a good nucleophile?

A

a strong enough base must deprotonate it

157
Q

why are terminal alkynes converted to good nucleophiles?

A

create a nucleophile that can react with a methyl or primary alkyl halide

158
Q

Alkynide ion reactivity

A

act as bases with secondary or tertiary alkyl halides to cause elimination instead of substitution

159
Q

alkylation mechanism

A
  • proton transfer first
  • alkyne loses H in proton transfer
  • results in strong, small, nuc/base that can undergo Sn2 and add what ever group there is to add
  • stepwise
160
Q

why cant the substrate be hindered for alkylation?

A

E2 will happen

161
Q

is hydrohalogenation of alkynes mark or anti mark?

A

mark addition

162
Q

termolecular equation and when it us used

A

Rate=k[alkyne][HX]^2

for alkyne hydrohalogenation

163
Q

What does excess HX result in for hydrohalogenation?

A

geminal dihalide(add 2 X groups to the carbon)

164
Q

difference between alkene and alkyne hydrohalogenation

A

rate equation and excess mechanism

165
Q

similarity between alkene and alkyne hydrohalogenation

A

same regiochemistry

166
Q

does hydrohalogenation of alkynes have stereochem?

A

no

167
Q

why can alkynes add multiple X groups in hydrohalogenation?

A

multiple pi bonds

168
Q

terminal alkynes as acids

A

weak acids

169
Q

is alkyne catalyzed hydration mark or anti mark?

A

mark hydration

170
Q

solvent for alkyne acid catalyzed hydration

A

HgSO4 to compensate for the slow reaction rate that results from a vinylic carbocation

171
Q

result of alkyne acid catalyzed hydration

A

mark addition of H and OH across pi bond

172
Q

alkyne acid catalyzed hydration reagent(s)

A

H2SO4 and H2O

173
Q

taumtomer

A

constitutional isomers that rapidly interconvert via proton migration in equilibrium with one another

174
Q

tautomers vs resonance

A

resonance structures are not in equilibrium and the resonance structures are different compounds

175
Q

tautomerization in acid catalyzed hydration of alkynes

A
  • cant be prevented
  • favors ketone a lot because C=O is more stable than C=C
  • between enol and ketone
  • breaks bonds and moves them around the molecule
176
Q

what type of chemical reaction is acid catalyzed hydration of alkynes?

A

acid-base reaction

177
Q

Is hydroboration/oxidation of alkynes mark or anti mark?

A

anti mark

178
Q

result of hydroboration/oxidation of alkynes

A

an enol that will quickly tautomerize

179
Q

tautomerization in hydroboration/oxidation of alkynes

A

-catalyzed by base

180
Q

difference between tautomerization in hydroboration/oxidation of alkynes and acid catalyzed hydration of alkynes

A

in hydroboration/oxidation it is catalyzed by a base and in acid catalyzed hydration it is catalyzed by an acid

181
Q

what happens to the resonance stabilized intermediate in acid catalyzed hydration of alkynes?

A

it is deprotonated to yield a ketone

182
Q

Function of OH in hydroboration/oxidation of alkynes

A

deprotonate enol to generate enolate ion

183
Q

function of H2O in hydroboration/oxidation of alkynes

A

protonate enolate ion to generate an aldehyde

184
Q

hydroboration/oxidation of alkynes reagents and solvents

A

1) BH3 THF

2) H2O2, NaOH

185
Q

result of hydroboration/oxidation of alkynes

A

Add H and BH2 across a pi bond

186
Q

purpose of bulky borane reagents in hydroboration/oxidation of alkynes

A

to prevent the second unit of BH3 from reacting with the intermediate and prevent yield of undesirable side products

187
Q

Hydration of terminal alkynes guidelines

A
  • mark hydration leads to a ketone

- anti-mark hydration leads to an aldehyde

188
Q

hydrogenation of alkynes reagent and solvent

A

2H2

Pt

189
Q

Result of hydrogenation of alkynes

A

alkane

190
Q

hydrogenation of alkynes intermediate and explanation

A

Cis intermediate because of syn addition

191
Q

What type of catalyst is used in hydrogenation of alkynes?

A

a heterogenous catalyst

192
Q

Why cant hydrogenation of alkynes result in chiral products?

A

2 hydrogens are added to a carbon

193
Q

How can alkynes be made into cis alkenes?

A
  • a poisoned or deactivated catalyst
  • the catalyst will catalyst the frist, but not the second hydrogenation reaction
  • syn addition
  • lindlar’s catalyst and P-2(NI2B complex)
  • gives 2 instead of 4 H
  • stops reaction halfway
194
Q

How can alkenes be made into trans alkenes?

A
  • single radical electron transfer
  • NH3(l) solvent
  • single electron goes to one side of triple bond, that atom has a pair and other atom is a radical because the 2 bonded electrons split
195
Q

halogenation of alkynes mechanism

A

still unknown

196
Q

products of halogenation of alkynes

A

both syn and anti addition

197
Q

how are products of halogenation of alkynes different than alkenes?

A

only anti addition is observed in alkenes

198
Q

Ozonolysis of alkynes

A
  • pi system is completely broken
  • alkyne carbons are fully oxidized
  • for internal alkynes: cleavage followed by addition of water yields carboxylic acids, split down left side of bond but yields symmetrical product
  • for terminal alkynes: split down middle of the bond, results in assymetrical product. Cleavage then addition of water results in terminal side being converted into CO2
199
Q

What is unique about ozonolysis of alkynes?

A

only way to make carboxylic acid so far

200
Q

how do free radicals form?

A

homolytic bond cleavage-one electron goes to each atom

201
Q

hybridization of free radicals

A

sp2 hybridized quickly interconverting between sp3 hybridized due to the number of non-bonding electrons

202
Q

free radical geometry

A

trigonal planar

203
Q

free radical stereochem

A
  • flat
  • resemble carbocations
  • can be attacked from either face
  • stereoselective-makes both enantiomers
204
Q

role of hyperconjugation with free radicals

A

groups that donate electrons to free radicals will help stabilize it due to hyperconjugation

205
Q

role of resonance with free radicals

A

allylic and benzylic radicals are especially stable due to radicals

206
Q

which radicals are not stablilized by resonace?

A

vinylic and aryl radicals

207
Q

relationship between homolytic BDE and stability of the radical

A

indirect

208
Q

Relationship between BDE and ability of homolytic cleavage to occur

A

indirect

209
Q

why does hyperconjugation stabilize radicals?

A

more R groups

210
Q

why are vinylic and aryl rings more uncommon with radicals?

A

it takes a lot of energy to remove hydrogens from them

211
Q

most common radical forming mechanism

A

H abstraction

212
Q

is resonance or hyperconjugation more stabilizing?

A

resonance

213
Q

BDE of weak bonds

A

low

214
Q

how do weak bonds react when forming radicals?

A
  • hard to pull off H atom

- leads to unstable intermediate

215
Q

Radical mechanism patterns

A

Initiation: no radical to radical through homolytic cleavage

Propogation: location of unparied electron is move about the molecule

Termination: 2 radicals annihilate each other by forming a bond-radical to no radical

216
Q

Reactions that result in radicals

A
  1. Halogenation of alkene: tertiary radical intermediate, X2 and hv
  2. halogenation of alkene: hv and NBS(to avoid addition reaction), adds Br, radical intermediates with resonance, pi bond doesn’t allow for normal bromination, has resonance which can yield multiple products
  3. Hydrohalogenation of alkene in the presence of peroxides(ROOR): anti mark, tertiary radical intermediate, O-O bond is radical initiator bc bond is weak
217
Q

initiators

A
  • required by radical reactions

- can be heat

218
Q

regioselectivity of radical halogenation

A
  • occurs at most substituted C because that will form the most stable radical intermediate
  • bromination is significantly more selective than chlorination
  • Cl is regioselective and Br is regiospecific
  • Br has 1 major product, Cl has 1 major and 1 minor product
219
Q

Hammond postulate in radical reactions

A
  • Br has higher preference in secondary halogenation product
  • large energy differences in bromination, smaller energy differences in chlorination
  • Chlorination is exergonic, bromination first propogation is endergonic
  • both endergonic overall
  • in chlorination, energy is close to starting material
220
Q

anti-mark hydrohalogenation of alkenes reagents

A

Hbr, ROOR

CHM 241 Dr. Erb (4 decks)

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