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Organic Chemistry 1 > Chapter 8 > Flashcards

Chapter 8 Flashcards

(85 cards)

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1
Q

What is the opposite of the addition reaction?

A

Elimination reaction

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2
Q

What happens to the C-C double bond (pi bond) in an addition reaction?

A

The C-C double bond (pi bond) is converted to two new sigma bonds

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3
Q

Where does the H go in an addition reaction?

A

H is attached to the carbon with the most H’s (least substituted)

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4
Q

Where does the positive charge (+) go in an addition reaction?

A

The positive charge (+) is added to the other carbon (that the H is not attached to) that is most substituted (has the most C’s)

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5
Q

How are alkenes present in nature?

A
  • Responsible for many different odors
  • Can be used for signals of reproduction
  • Double bonds can be found in oil in the ground (petroleum)
    • Propylene and ethylene (both containing double bonds) can be made from cracking petroleum
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6
Q

What is an isolated double bond?

A

A double bond that is not near/next to any other double bonds

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7
Q

What is a conjugated double bond?

A

A double bond that is next to another/other double bonds

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8
Q

What kind of double bond has special character- isolated double bonds or conjugated double bonds?

A

Conjugated double bonds

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9
Q

What are the steps for giving IUPAC names to alkenes?

A
  1. Identify the parent chain that INCLUDES the double bond
  2. Identify and name the substituents
  3. Assign a locant (number and prefix if necessary) to each substituent
    • Give the C-C double bind the lowest number possible
  4. List the numbered substituents before the parent name in alphabetical order (ignoring the prefixes for order)
  5. The C-C double bond locant is placed before the parent name or just before the -ene suffix
    • The Z and S should be added to the beginning to describe the orientation in parenthesis
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10
Q

What does Z configuration mean?

A

Z means cis configuration

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11
Q

What does S configuration mean?

A

S means trans configuration

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12
Q

True or false: The parent chain must include the C-C double bond, so the shorter chain including the double bond should be chosen over the longer chain that doesn’t include the double bond

A

True

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13
Q

How do you know which number to give the C-C double bond since it is in between two C’s? (How do you know if the double bond is labeled 2 vs. 3?)

A

The double bond should always be listed as the lower number carbon that it is between (if it is between carbon 2 and 3, it should be listed as 2)

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14
Q

True or False: Addition and elimination reactions are in equilibrium

A

False: Addition and elimination are equilibrating reactions, and a side is favored is depending on temperature

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15
Q

When temperature is increased, is entropy or enthalpy more important?

A

Entropy- means a bigger entropy term

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16
Q

When entropy is positive, does it favor or disfavor delta G?

A

Favors

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17
Q

What kind of reaction is favored by enthalpy- addition or elimination?

A

Addition

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18
Q

Why is it that addition reactions are favored by enthalpy?

A

Addition reactions are favored by enthalpy because sigma bonds are strong/more stable than pi bonds
-Lower energy when bonds form–> more stable

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19
Q

What kind of reaction occurs when the energy harvested is more than the energy used?

A

Exothermic

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20
Q

What kind of reaction is favored by entropy- addition or elimination?

A

Elimination

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21
Q

Why is it that elimination reactions are favored by entropy?

A

When one molecule is broken into two molecules, entropy increases
-Goes from low entropy to high entropy

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22
Q

What is enthalpy (delta H)?

A

The total energy of a system

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23
Q

What is entropy (delta S)?

A

The disorder of a system

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24
Q

Summary of addition and elimination based on temperature

A
  • At LOW temperatures, ENTHALPY dominates, and ADDITION reactions are favored
  • At HIGH temperatures, ENTROPY dominates, and ELIMINATION reactions are favored
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25
What is hydrohalogenation?
The addition of a halogen and a H to an alkene | -HCl, HBr, or HI
26
When an alkene is symmetrical, where does the hydrogen go and where does the halogen go?
Doesn't matter | -Both sides are the same
27
When an alkene is not symmetrical, what determines where does the hydrogen and the halogen go?
Regioselectivity
28
What is regioselectivity?
When a process favors a bond formation over any other possible formation
29
What are regioisomers?
Isomers of a compound with the same atom-makeup but different connectivity of the atoms
30
What is Markovnikov addition?
A pattern that Markovnikov observed in unsymmetrical alkenes - H atoms tend to add to the carbon with more H atoms - Halogen goes to the more substituted carbon
31
What happens when peroxides are used with a hydrogalogenation (hydrogen peroxide= ROOR)?
Anti-Markovnikov regioselectivity
32
What is Anti-Markovnikov addition?
When the opposite regioselectivity is observed in an addition reaction - The H atoms add to the more substituted carbon - Halogen goes to the carbon with more H atoms
33
What does the presence of peroxide in a hydrohalogenation reaction allow us to do?
It allows the regioselectivity of the hydrohalogenation addition to be controlled by either its presence or absence - Can force Markovnikov addition (without ROOR) - Can force Anti-markovnikov addition (with ROOR)
34
What are the steps of hydrohalogenation?
1. Proton transfer (hydration) - The alkene is protonated, forming a carbocation intermediate and a bromide ion 2. Nucleophilic attack - The bromide ion functions as a nucleophile and attacks the carbocation intermediate
35
Which step has a higher energy barrier- proton transfer or nucleophilic attack, making it the rate determining step?
Proton transfer
36
What are the two possible products of hydrohalogenation?
1. Anti-Markovnikov pathway - Forms a secondary carbocation 2. Markovnikov pathway - Forms a tertiary carbocation
37
Which product is formed (generally) for hydrohalogenation: Anti-Markovnikov or Markovnikov and why?
Markovnikov product is formed because the carbocation is more stable than the anti-markovnikov - Tertiary vs. secondary carbocations - Faster reaction
38
When hydrohalogenation forms a chiral center, which enantiomer is formed more?
Neither- they form in equal amounts - The carbocation is flat (trigonal planar) - Allows for attack from either side of the empty orbital with equal probability
39
What is a hydride shift?
When a carbocation rearranges a hydrogen to become more stable - Rearrange from secondary to a tertiary carbocation - More stable form will be formed more
40
What is a methyl shift?
When a carbocation rearranges a methyl group to become more stable - Rearrange from a secondary to a tertiary carbocation - More stable form will be formed more
41
What is acid-catalyzed hydration?
When the components of water (H and OH) are added across the pi bond - Acids have lots of protons - Follows Markovnikov regioselectivity
42
Where is the OH added in an acid-catalyzed hydration?
OH is added to the more substituted carbon of the alkene
43
What are the steps of an acid-catalyzed hydration?
1. Proton transfer (hydration) - The alkene is protonated, forming carbocation intermediate 2. Nucleophilic attack - Water functions as a nucleophile and attacks the carbocation intermediate - Creates an oxonium ion 3. Proton transfer (deprotonation) - Water functions as a base and deprotonates the oxonium ion, yielding the alcohol product
44
What is an oxonium ion?
An oxygen cation with 3 bonds
45
True or false: The reactants and products of acid-catalyzed hydration are in equilibrium?
True
46
When water is added to an alkene, what is created?
An alcohol
47
If you wanted to synthesize an alcohol from an alkene, what would you do?
Use excess water (hydration)
48
If you wanted to synthesize an alkene from alcohol, what would you use?
A concentrated acid | -Would not add water to the reaction (dehydration)
49
If a chiral center is formed in hydrohalogenation, what fraction of R and S is formed?
50/50 | -Racemic mixture (mixture of R and S)
50
What is syn-addition?
When the H and X are added from the same side
51
What is anti-addition?
When the H and X are added from opposite sides
52
When a chiral center is formed, what is the stereoselectivity? -Is the reaction syn-addition or anti-addition?
Both - X can be added from either side(s) of the carbocation - Since it is flat from trigonal planar
53
What is stereoselectivity?
When a stereoisomer is formed in greater amounts that the other possible stereoisomers
54
What is oxymercuration-demercuration?
A form of hydration in which no rearrangements occur - Markovnikov addition of H and OH - No mixture of products
55
What acts as the acid in an Markovnikov acid-catalyzed hydration reaction?
H+
56
What acts as the acid in an oxymercuration-demercuration reaction?
Mercuric cation | -A cation of mercury (Hg)
57
What is the difference between a pi bond attack on a proton (H+) and on a mercuric cation?
``` Proton: -Carbocation formed that can rearrange Mercuric cation: -The carbocation will be stabilized by the same mercury (forming a cyclic intermediate), where it is no longer a carbocation -No rearrangements occur ```
58
What is a mercurinium ion?
The intermediate formed during oxymercuration-demercuration | -Contains mercury (Hg)
59
Is the mercurinium ion formed during an oxymercuration-demercuration reaction an electrophile or a nucleophile?
It is an electrophile | -Easily attacked by a nucleophile
60
What is commonly used in a oxymercuration-demercuration reaction to replace the HgOAc group?
NaBH4
61
What are the two common reagents used for a oxymercuration-demercuration reaction?
1. ) Mercury acetate, H2O - Hg(OAc)2 2. ) NaBH4
62
What is hydroboration-oxidation?
The addition of borane (BH3) followed by oxidation
63
What kind of regioselectivity does hydroboration-oxidation undergo: Markovikov addition or anti-markovnikov addition?
Anti-markovnikov addition because of steric strain - The boron goes to the less substituted carbon - The hydrogen will undergo a hydride shift onto the more substituted carbon
64
How is hydroboration-oxidation stereospecific?
Only syn-addition occurs
65
What are the common reagents used in a hydroboration-oxidation reaction?
1. ) Borane (BH3 x THF) | 2. ) Hydrogen peroxide (H2O2), Sodium hydroxide (NaOH)
66
What are the steps of hydroboration-oxidation?
1.) Hydroboration 2. ) Proton transfer - A hydroxide ion functions as a base and deprotonates hydrogen peroxide, creating a hydro peroxide 3. ) Nucleophilic attack - The hydroperoxide functions as a nucleophile and attacks the borane 4. ) Rearrangement - An alkyl group migrates, losing a hydroxide ion 5. ) Nucleophilic attack - A hydroxide ion functions as a nucleophile and attacks a trialkoxyborane (a boron atom attached to 3 oxygens) 6. ) Loss of a leaving group - An alkoxide ion is lost, removing the negative charge from the boron 7. ) Proton transfer - The alkoxide ion is protonated
67
When chiral centers are formed from a hydroboration-oxidation reaction, what are the products that are formed?
A pair of enantiomers
68
What is catalytic hydrogenation?
The addition of H2 across a C=C double bond | -Uses a catalyst in a solid or powder form
69
What kind of catalyst is required for catalytic hydrogenation?
A metal catalyst such as platinum or nickel
70
What does the alkene turn into when undergoing a catalytic hydrogenation?
An alkane
71
What is the stereospecifity observed during catalytic hydrogenation?
Only syn addition is observed
72
Why is only syn addition observed?
The metal surface binds the H2 and the alkene, so the H atoms must be added to the same side of the alkene
73
When a symmetrical alkene is undergoing catalytic hydrogenation, what will the product be?
A meso compound
74
What is a heterogeneous catalyst?
A kind of catalyst that does not dissolve in reaction medium | -Pt or Pd metal
75
What is a homogeneous catalyst?
A kind of catalyst that does dissolve in reaction mediums | -Serves as a solvent`
76
True or false: If a chiral catalyst is used, it is possible to synthesize only one enantiomer as the major product
True
77
What is halogenation?
The addition of two halogen atoms across a C=C double bond
78
What halogens are good for halogenation?
Chlorine (Cl2) and Bromine (Br2)
79
Why are halogens iodine and fluorine bad to use for halogenation?
- Iodine (I2) is too slow | - Fluorine (F2) is too fast
80
What is the stereoselectivity of halogenation?
Anti-addition | -Halogens added from opposite sides
81
What happens when a nucleophile reaches a halogen during halogenation? (Br2)
It will induce a dipole between the two halogen atoms
82
What acts as a nucleophile in halogenation?
The alkene
83
Why is only anti-addition observed for halogenation?
The attachment of one of the halogens will block the other halogen from adding to the same side
84
What kind of intermediate is formed during halogenation (Br2)?
A bromonium ion intermediate
85
What steps create a bromonium ion intermediate?
Nucleophilic attack & loss of leaving group (SN2: concerted) - The alkene functions as a nucleophile and attacks bromine, expelling the other bromine as a leaving group - A bridged intermediate is formed called a bromonium ion

Organic Chemistry 1 (3 decks)

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