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Organic Chemistry I > Alkene and Alkyne Mechanisms > Flashcards

Alkene and Alkyne Mechanisms Flashcards

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1
Q

Name this Alkene mechanism

A

Halogenation (X2 addition)

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2
Q

Name this Alkene overall transformation

A

Halohydrin formation (X2+H2O/ROH)

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3
Q

Name this Alkene overall transformation

A

Acid-Catalyzed Addition of Water

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4
Q

Name this Alkene overall transformation

A

Oxymercuration/Reduction

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5
Q

Name this Alkene overall transformation

A

Hydroboration/Oxidation

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6
Q

Name this Alkene overall transformation

A

Catalytic Hydrogenation. Stereospecific. Reduction of alkene to alkane

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7
Q

Name this Alkene overall reaction

A

Epoxidation

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8
Q

Name this Alkene overall transformation

A

Ozonolysis

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9
Q

Name this Alkene overall transformation

A

Cycloproponation

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10
Q

Name this Alkene overall transformation

A

Hydroxylation

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11
Q

Name this Alkene overall transformation

A

Oxidative Cleavage of syn-Glycols with HIO4

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12
Q

Alkene is a loose sea of electrons that reacts with a strong acid to break the bond from halide

A

H-X Addition

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13
Q

What is DCM?

A

Organic solvent dichloromethane (or methylene chloride) that does not participate in the rxn but gets the compounds into a reactive medium

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14
Q

If Cl and Cl or Br and Br atoms join, what happens to the electrons?

A

The partial (+) and partial (-) charges (dipole interactions) on both of the highly electronegative atoms will drive the electrons to one side and cause a chemical reaction

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15
Q

What makes this bromonium ring reactive, yet “happy”?

A

It wants to be broken open The bromonium ring structure is happy because it has a full octet, but it is highly reactive due to the 3-angle ring strain (bond angle about 60 degrees) and all electrons are eclipsed by each other. Also, bromine has a (+) charge. Since bromine is electronegative, so it wants electrons.

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16
Q

Does a bond become a dash or a wedge when you attack the back side of a wedge?

A

dash

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17
Q

Name this Alkene overall transformation

A

Halogenation (X2 addition)

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18
Q

What is regioselectivity?

A

rxn where one constitutional isomer is favored over the other

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19
Q

What is stereoselective rxn?

A

rxn where one stereoisomer is formed in preference (R/S)

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20
Q

Stereospecific rxn

A

What time of rxn results in one stereoisomer forming based on the mechanism alone (always san/anti or inversion of stereochemistry

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21
Q

Name this Alkene mechanism

A

Halogenation (X2 addition)

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22
Q

Halogenation (X2 addition) mechanisms produce a mixture of enantiomers. Why?

A

The molecule has 2 sigma* bonds (anti) which are empty space that can accept electrons.

Nucleophiles such as Br2 or Cl2 attack with filled MO. To break the sigma bond, you must attack the empty version of the sigma bond which is the sigma* bond. Then, put electrons in empty MO (sigma*).

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23
Q

Why don’t we use F2 or I2 in Halogenation (X2 addition)?

A

Both work, but F2 is explosive and I2 produces unstable products that decompose readily

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24
Q

Name this Alkene mechanism

A

Halohydrin formation (X2+H2O/ROH)

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25
Q

In a regioselective rxn, why does the nucleophile attack the more substituted carbon?

A

Nucleophile attacks the longer, weaker bond. The carbon on the weaker bond can handle the partial charge better because it is the most stable with more substitution and hyperconjugation.

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26
Q

Name this Alkene mechanism

A

Acid-Catalyzed Addition of Water

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27
Q

When a strong acid and water are mixed completely with an alkene, what is the product?

A

An alcohol

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28
Q

Properties of Acid-Catalyzed Addition of Water Alkene Mechanisms

A
  1. Markov. In the RDS: Acid being added to an alkene (Markov. - proton goes on the carbon with more protons) forming a carbocation
  2. Intermediate is a carbocation. *Look for carbocation rearrangements (1,2-methyl shift, 1,2- hydride shift, and ring expansion)
  3. Add water and remove the proton with solvent. Rxn is catalytic in hydronium or proton (does not officially get consumed in the reaction, regenerated in the product). There is a racemic mixture of products if there is stereochemistry on your substrate
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29
Q

H2SO4 + H2O dissociates completely to form

A

H3O+ (does the chemistry) and HSO4- (spectator)

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30
Q

What is the product of this Acid-Catalyzed Addition of Water Alkene mechanism?

A

tertiary alcohol

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31
Q

What are the 3 types of Alkene hydration (adding water across an alkene) mechanisms?

A
  • *1. Acid-Catalyzed Addition of Water** - Catalytic. Goes through a carbocation intermediate. First step is an acid addition, Markov.
  • *2. Oxymercuration/Reduction** - Goes through mercuronium ring, water attacks the more substituted carbon. No rearrangements. Alcohol ends up where starting alkene was, Markov. Mixture of enantiomers.
  • *3. Hydroboration/Oxidation** - Enantiomer of Syn addition of water, anti-Markov. Only + enant if there is stereochemistry
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32
Q

Name this Alkene mechanism

A

Oxymercuration/Reduction

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33
Q

What two mechanisms are being compared in this transformation?

A

oxymerization/reduction and acid-catalyzed addition of H2O

34
Q

Properties of Oxymercuration/Reduction

A

Properties:

  1. Markov-addition of water. H goes on carbon with more H’s (protons) and OH went on the carbon with less protons
  2. Goes through a Hg(+) mercuronium ring intermediate. Origin of regioselectivity when H2O attacks the more substituted carbon.
  3. Distereoselective= anti addiction of water. When the ring pops open after adding water, the thing added and the thing that popped open will be anti to each other.
  4. No carbocations, so no rearrangements.
35
Q

What two mechanisms are being compared in this transformation?

A

oxymerization/reduction and acid-catalyzed addition of H2O

36
Q

Name this Alkene mechanism

A

Hydroboration.
Boron lines up on carbon with more hydrogens and the hydride will line up with the carbon with less hydrogens. Syn insertion reaction because boron and hydrogen are being added to the same side of the alkene.

37
Q

Define Anti-Markov

A

when a proton gets added to the carbon with less hydrogens on it

38
Q

What is syn addition of water?

A 
The water (H and OH) get added on the same side (dash and dash). 
Opposite of anti where the addition of water are opposites (one on wedge and one on dash).
39
Q

In hydroboration, what are the 2 reasons boron chooses carbon with less hydrogens:

A
  1. Electronics - B is partial (-) and carbon with less hydrogens is partial (+)
  2. Sterics - boron will try to be as far away from a group as possible to avoid bumping electron clouds. The more sterically hindered alkene, the higher selectivity for anti-markov
40
Q

What is a concerted rxn?

A

all breaking/forming bonds happen at the same time (no intermediate step)

41
Q

3 ways of adding H2O and their transformations

  1. Acid-Catalyzed Addition of Water
  2. Oxymercuration/Reduction
  3. Hydroboration/Oxidation
A
42
Q

Name this Alkene reaction

A

Catalytic Hydrogenation.

43
Q

Is Benzene an alkene?

A

No, leave it alone.

44
Q

Drawing that represents the alkene interacting with a metal surface in catalytic hydrogenation

A

the metal catalyst (Pd) is a surface of atoms and the alkene can only interact with one side of the surface at a time which is the origin of diastereoselectivity.

45
Q

Properties of Catalytic hydrogenation reactions

A
  1. Syn addition of H2
  2. Common Catalysts: Pd/C, PtO2
  3. Using gas (H2) - typically reduces all alkenes (using an excess amount of hydrogen)
  4. Sensitive to sterics: Reduce the side of the alkene that is less blocked by sterics
46
Q

Define chemoselectivity

A

Reducing selectively one pi system over all others. Just reduces alkene.

47
Q

For surface rxns, such as catalytic hydrogenations, we reduce the side of the alkene that is less

A

sterically hindered

48
Q

Define catalyst

A

speeds up the reaction by lowering the activation energy/ barrier but is not consumed

49
Q

What is reduction/oxidation in General Chemistry?

A

oxidation is loss of electrons and reduction is the gain of electrons.

50
Q

What is reduction/oxidation in Organic Chemistry?

A

Reduction is a gain in hydrogens and oxidation is a gain in oxygens.

51
Q

Name this Alkene mechanism

A

Epoxidation

52
Q

Properties of epoxidation reactions

A
  1. Concerted (no carbocations, no intermediates)
  2. Substituents on alkene remain pointing the same way
53
Q

What are concerted reactions?

A

all breaking/forming bonds happen at the same time.

Substituents stay pointing in the same direction that they already were, or they will stay pointing in opposite directions if they already were.

DRAW ALL AT THE SAME TIME.

54
Q

What is MCPBA and what family does it belong to?

A

meta-chloroperoxybenzoic acid belonging to the peroxy acid family

55
Q

What causes the reaction to happen in a concerted epoxidation reaction?

A

In a concerted rxn, there is no time to equilibrate. MCPBA is what causes the concerted rxn, not structure. Cis-Alkenes to cis Alkenes or trans Alkenes to trans Alkenes

56
Q

Name this Alkene overall transformation

A

Ozonolysis

57
Q

Name this Alkene mechanism

A

Ozonolysis

58
Q

Examples of Ozonolysis

A

cut and oxidize the alkene bonds to make carbonyls

59
Q

Why is -78 degrees C a common temperature to perform reactions under in organic chemistry?

A

Cold temperature allows chemists to control the reaction and avoid overheating the reaction and potentially dissolving a solvent or exploding.

Equilibrium temp of ice in water is 0 degrees C.

The equilibrium temperature of dry ice in isopropanol (IPA) is -78 degrees Celsius.

60
Q

What does ozone O3 look like? How many resonance structures does it have?

A

2 resonance structures

61
Q

What is contained in ozonolysis steps 1&2?

A

Ozonolysis step 1 contains O3, MeOH, and it is at -78 degrees C

Ozonolysis step 2 contains Zn, AcOH, H2O OR DMS (CH3SCH3)

62
Q

What is the Simmons-Smith reaction?

A
63
Q

What type of formation is this?

A

Carbene formation

64
Q

Name this Alkene mechanism

A

Cyclopropanation

65
Q

What is a carbene?

A

A highly unstable intermediate because carbon only has 6 electrons, not a full octet. Carbenes are Sp2 hybridized.

66
Q

Carbenes plus an alkene make

A

3 membered rings or cyclopropane

67
Q

Name some properties of hydroxylation

A
  1. No rearrangements, every step is concerted
  2. Stereochemistry is retained (starts cis ends cis/starts trans ends trans)
  3. OsO4 very toxic reagent (chemists use a catalytic amount which is way less of an amount to endorse green chemistry).
68
Q

What is another way of naming glycol?

A

1,2 - diol

69
Q

What type of ring is necessary to make in oxidative cleavage of syn-glycols?

A

We must be able to make a 5 membered ring. The only way we can make a 5-membered ring is if the OH’s are pointing on the same side of the compound. Then, the ring decomposes and we get our product. Diols (glycols) pointing in opposite directions don’t react.

70
Q

Example of why it is geometrically impossible for anti-OH’s to make a 5-membered ring and undergo oxidative cleavage.

A

periodic acid is a way to take 2 OH and cut the bond in between and made a carbonyl. Have to be cis and adjacent

71
Q

Name this Alkene reaction

A

Oxidative Cleavage of syn-Glycols

72
Q

Rules for Alkyne Nomenclature

A
  1. Alkynes demand priority: Gets lowest number Carbon. Priority demanding group regardless of any other substituents 2. Name the longest chain that contains the Alkyne, drop “-and” and replace with the “-yne”
73
Q

Name this Alkyne overall transformation

A

Alkyne H-X Addition

74
Q

When a compound has both an Alkene and Alkyne, who gets priority?

A

Alkene priority = Alkyne priority, except in a tire alkene wins

75
Q

Hammond’s postulate states that TS is going to be most similar to the things closest in energy. If I know the relative energy of intermediates then I know

A

the relative rates of formation of those intermediates. TS is often closets in energy to the intermediate.

76
Q

Who is more thermodynamically stable, Alkene or Alkyne?

A

Alkene

77
Q

Just because an Alkyne has more internal energy than an alkene does not mean that it will react quicker. Instead, what do we look at to determine the relative reaction rates?

A

Activation barrier or activation energy

78
Q

Carbocation stability comes from what 2 things?

A

Hyperconjugation and resonance

79
Q

When comparing a secondary carbocation and a secondary vinyl carbocation, which is more stable and therefore quicker to form and why?

A

The secondary carbocation is more stable than the secondary vinyl carbocation because the vinyl carbocation sits in an empty Sp2 orbital with ZERO hyperconjugation. The secondary carbocation rate to form will require less energy and therefore be faster.

80
Q

Are alkene and alkyne reactions endo or exothermic?

A

Exothermic; they release heat from losing a pi bond.

81
Q

Name this Alkyne mechanism

A

H-X Addition to Alkynes

82
Q

Does H-X Addition to Alkynes participate in Markov.?

A

Yes!

Organic Chemistry I (12 decks)

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