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Questions and Answers
In electrophilic addition reactions of HX to an alkene, which of the following statements accurately describes the regioselectivity observed, based on Markovnikov's rule?
In electrophilic addition reactions of HX to an alkene, which of the following statements accurately describes the regioselectivity observed, based on Markovnikov's rule?
- The halogen atom is captured by the alkene carbon having the fewest substituents.
- The hydrogen atom is captured by the alkene carbon having the fewest hydrogens.
- The hydrogen atom is captured by the alkene carbon having the most hydrogens. (correct)
- The halogen atom demonstrates no regioselectivity; the products are formed in equal amounts.
Tertiary carbocations are generally less stable than primary carbocations due to reduced hyperconjugation and inductive effects.
Tertiary carbocations are generally less stable than primary carbocations due to reduced hyperconjugation and inductive effects.
False (B)
What is the driving force behind anti-addition in the addition of halogens to alkenes, and why does it favor the formation of trans products?
What is the driving force behind anti-addition in the addition of halogens to alkenes, and why does it favor the formation of trans products?
Steric strain
In alkene hydrogenation, a reaction defined as a reduction, alkenes react readily with ______ gas in the presence of a metal catalyst, leading to a gain of electron density.
In alkene hydrogenation, a reaction defined as a reduction, alkenes react readily with ______ gas in the presence of a metal catalyst, leading to a gain of electron density.
Match each method of alkene hydration with its corresponding regioselectivity.
Match each method of alkene hydration with its corresponding regioselectivity.
Why is brute-force hydration not considered ideal for research or undergraduate laboratory environments?
Why is brute-force hydration not considered ideal for research or undergraduate laboratory environments?
In the oxymercuration-demercuration process, the treatment of an alkene with sodium borohydride (NaBH4) in the second step is essential for Markovnikov addition of water.
In the oxymercuration-demercuration process, the treatment of an alkene with sodium borohydride (NaBH4) in the second step is essential for Markovnikov addition of water.
In hydroboration of alkenes, what term describes the stereochemistry of the -H and -OH addition to the double bond?
In hydroboration of alkenes, what term describes the stereochemistry of the -H and -OH addition to the double bond?
During alkene hydrogenation, the addition of hydrogen occurs in a specific manner referred to as ______, indicating that both hydrogen atoms add to the same side of the alkene.
During alkene hydrogenation, the addition of hydrogen occurs in a specific manner referred to as ______, indicating that both hydrogen atoms add to the same side of the alkene.
Match the reagents used in alkene hydrogenation with their description or composition:
Match the reagents used in alkene hydrogenation with their description or composition:
Which of the following is true regarding the selectivity of alkene hydrogenation?
Which of the following is true regarding the selectivity of alkene hydrogenation?
In the context of alkene ozonolysis, the initial step involves the addition of ozone (O3) to the alkene, typically at high temperatures to accelerate the reaction.
In the context of alkene ozonolysis, the initial step involves the addition of ozone (O3) to the alkene, typically at high temperatures to accelerate the reaction.
What specific functional groups are produced when an alkene undergoes ozonolysis?
What specific functional groups are produced when an alkene undergoes ozonolysis?
Alkene oxidative cleavage involves the addition of ______ solution to an alkene, resulting in the splitting of the alkene and the full oxidation of the resulting fragments.
Alkene oxidative cleavage involves the addition of ______ solution to an alkene, resulting in the splitting of the alkene and the full oxidation of the resulting fragments.
Match the ozonolysis reagents with their role in the reaction:
Match the ozonolysis reagents with their role in the reaction:
What products are produced when an alkene group is terminal during oxidation with KMnO4?
What products are produced when an alkene group is terminal during oxidation with KMnO4?
In alkene oxidation using KMnO4, the purple color of the KMnO4 solution remains unchanged if the solution reacts with an alkene.
In alkene oxidation using KMnO4, the purple color of the KMnO4 solution remains unchanged if the solution reacts with an alkene.
What characteristic of alkyl groups makes carbocations more stable in terms of electron donation?
What characteristic of alkyl groups makes carbocations more stable in terms of electron donation?
According to Markovnikov's rule, in the addition of HX to an asymmetric alkene, the ______ atom from HX attaches to the alkene carbon with the most hydrogen atoms already connected to it.
According to Markovnikov's rule, in the addition of HX to an asymmetric alkene, the ______ atom from HX attaches to the alkene carbon with the most hydrogen atoms already connected to it.
Match each type of carbocation with its relative stability:
Match each type of carbocation with its relative stability:
Which statement correctly describes the role of carbocation stability in Markovnikov's rule?
Which statement correctly describes the role of carbocation stability in Markovnikov's rule?
Addition of a halogen to a cyclic alkene gives exclusively the syn product due to minimal steric strain.
Addition of a halogen to a cyclic alkene gives exclusively the syn product due to minimal steric strain.
Name the three main methods used to achieve the hydration of an alkene.
Name the three main methods used to achieve the hydration of an alkene.
In alkene hydrogenation, the reaction is considered a ______ because the alkene carbon atoms gain electron density during the process.
In alkene hydrogenation, the reaction is considered a ______ because the alkene carbon atoms gain electron density during the process.
Match the specific type of bond with its behavior during alkene hydrogenation:
Match the specific type of bond with its behavior during alkene hydrogenation:
Why is alkene oxidation considered an oxidation reaction?
Why is alkene oxidation considered an oxidation reaction?
During ozonolysis, only ketones can be formed as products due to the reaction mechanism.
During ozonolysis, only ketones can be formed as products due to the reaction mechanism.
Why does the carbon atom lose electron density when it forms a C-O bound during oxidation?
Why does the carbon atom lose electron density when it forms a C-O bound during oxidation?
The driving force for anti-addition in halogenation of alkenes is ______ strain, which causes halogens to add on opposite sides of the molecule.
The driving force for anti-addition in halogenation of alkenes is ______ strain, which causes halogens to add on opposite sides of the molecule.
Associate the number of alkyl groups attached to the carbocation center with its relative stability.
Associate the number of alkyl groups attached to the carbocation center with its relative stability.
Flashcards
Markovnikov's Rule
Markovnikov's Rule
In electrophilic addition, the hydrogen atom attaches to the carbon with the most hydrogens, and the halogen attaches to the more substituted carbon.
Regiospecific Reaction
Regiospecific Reaction
A reaction where atoms go in specific positions.
Carbocation Stability
Carbocation Stability
Stability of carbocations increases with alkyl substitution due to electron-donating properties.
Halogen Addition and Induced Dipoles
Halogen Addition and Induced Dipoles
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Anti-Addition
Anti-Addition
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Stereospecific Reaction
Stereospecific Reaction
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Addition of Water to Alkenes
Addition of Water to Alkenes
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Brute-Force Hydration
Brute-Force Hydration
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Oxymercuration
Oxymercuration
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Hydroboration
Hydroboration
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Alkene Hydrogenation
Alkene Hydrogenation
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Reduction
Reduction
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Syn Addition
Syn Addition
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Oxidation
Oxidation
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Ozonolysis
Ozonolysis
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Alkene Oxidative Cleavage
Alkene Oxidative Cleavage
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Study Notes
Electrophilic Addition of HX and Markovnikov's Rule
- An electrophilic addition reaction is regiospecific
- Regiospecific reactions mean atoms attach to specific positions.
- In electrophilic addition of HX to an alkene, the hydrogen atom is captured by the alkene carbon with the most hydrogens.
- The halogen atom bonds to the most highly substituted alkene carbon atom.
- Carbocation stability determines the major product in such reactions.
- Alkyl groups (-R) are electron-donating, increasing carbocation stability.
- Carbocation stability order: tertiary > secondary > primary > methyl.
- Even if a primary carbocation is chemically reactive it has a higher activation energy than a tertiary carbocation.
- Because the first step is faster with a tertiary carbocation, the major product forms from a faster formation
Addition of Halogens to Alkenes
- Elemental halogens (X₂) are symmetrical and nonpolar.
- As bromine approaches the double bond, electrons are repelled, creating an induced dipole.
- The bromine molecule becomes polarized.
- The mechanism forming an induced-dipole is identical to London dispersion forces.
- Halogen addition to alkenes is stereospecific, resulting in particular 3-dimensional orientations.
- This is called anti-addition.
- Steric strain is the driving force
- When bromine atoms are trans, there is less steric strain.
Addition of Water to Alkenes
- Hydration is a reaction is when water is added to alkenes, forming alcohols.
- Three methods of hydration:
- Brute-force hydration follows Markovnikov addition.
- Oxymercuration follows Markovnikov addition.
- Hydroboration follows anti-Markovnikov addition.
Brute-Force Hydration
- Acid-catalyzed hydration of alkenes requires an acid catalyst
- A typical hydration medium is 50% H₂SO₄ and 50% H₂O
- Problems with brute-force hydration:
- Highly acidic conditions
- High temperatures
- Is ideal for industrial settings but is not suitable for research or undergraduate laboratory environments.
Oxymercuration
- Step 1 uses mercuric acetate.
- Step 2 uses sodium borohydride.
- Tetrahydrofuran (THF) is used as a solvent.
- Oxymercuration follows Markovnikov addition.
Hydroboration
- Anti-Markovnikov hydration occurs
- Syn-addition happens, where -H and -OH are added on the same side of the ring.
Alkene Hydrogenation
- Alkenes react with H₂ gas using a metal catalyst.
- Hydrogenation is reduction
- A reduction is defined as a gain of electrons or electron density.
- In >C=C< to >CH-CH<, carbon gains electron density.
- Reagents include: H₂ gas, Pt/C, Pd/C, and PtO₂.
- Platinum/Carbon catalyst (Pt/C): platinum powder spread over activated charcoal.
- Palladium/Carbon catalyst (Pd/C): palladium powder spread over activated charcoal.
- PtO₂ is Adam's reagent.
- Hydrogenation is a syn addition.
- Degrees of Unsaturation
- The number of degrees of unsaturation includes rings and double bonds
- Only C=C absorbs hydrogen, allowing determination of double bonds and rings in a compound.
- Hydrogenation Specificity:
- C=C bonds are reduced by H₂ on Pt/C.
- C=O, C=N, and benzene rings are not reduced this way.
Oxidation of Alkenes
- Oxygen to a carbon is oxidation.
- Oxidation is loss of electrons or electron density.
- C electronegativity is 2.5, and O electronegativity is 3.5.
- When making a C-O bond, electrons flow from the carbon to the oxygen, resulting in the oxidation of the carbon.
- Two types of oxidation:
- Ozonolysis
- Treatment with KMnO₄
Ozonolysis
- Aldehydes or ketones are formed.
- Reagents for the two-step reaction:
- O₃, CH₂Cl₂
- Zn/H⁺ or (CH₃)₂S
- It is possible to work backwards, beginning with the ozonolysis products.
Alkene Oxidative Cleavage
- Adding KMnO₄ to an alkene causes it to split -up and become fully oxidized.
- If the alkene group is terminal, bubbles of CO₂ are released
- Ketones cannot be further oxidized.
- A ketone cannot be further oxidized KMnO₄ solution is purple, but decolorizes when it reacts with an alkene.
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