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How to use the (E)-(Z) system?
How to use the (E)-(Z) system?
- Examine the two groups attached to one carbon atom of the double bond, figure out which of the two has the higher priority. 2. Do the same at the other carbon atom. 3. Compare the group of high priority on one carbon atom with the group of high priority on the other carbon atom. If the two groups of high priority are on the same side, they are Z; if not, they are E.
What does Z mean in the context of the (E)-(Z) system?
What does Z mean in the context of the (E)-(Z) system?
Means 'together'; the two groups of higher priority are on the same side of the double bond.
What does E mean in the context of the (E)-(Z) system?
What does E mean in the context of the (E)-(Z) system?
Means 'opposite'; the two groups of higher priority are on opposite sides of the double bond.
Are cis or trans isomers of alkenes more stable?
Are cis or trans isomers of alkenes more stable?
What is hydrogenation?
What is hydrogenation?
What affects the relative stabilities of alkenes?
What affects the relative stabilities of alkenes?
What is the nature of cycloalkenes with five carbon atoms or fewer?
What is the nature of cycloalkenes with five carbon atoms or fewer?
What are elimination reactions in organic chemistry?
What are elimination reactions in organic chemistry?
What are methods for alkene synthesis?
What are methods for alkene synthesis?
What are the best conditions to synthesize an alkene by dehydrohalogenation?
What are the best conditions to synthesize an alkene by dehydrohalogenation?
What conditions favor an E2 mechanism?
What conditions favor an E2 mechanism?
What is Zaitsev's rule?
What is Zaitsev's rule?
What happens when you use a small base like ethoxide or hydroxide?
What happens when you use a small base like ethoxide or hydroxide?
What is meant by kinetic control of product formation?
What is meant by kinetic control of product formation?
What happens if you use a bulky base like t-BuOK/t-BuOH?
What happens if you use a bulky base like t-BuOK/t-BuOH?
What is Hofmann's Rule?
What is Hofmann's Rule?
What must be the orientation of five atoms involved in the transition state of an E2 reaction?
What must be the orientation of five atoms involved in the transition state of an E2 reaction?
Why do the molecules have to be coplanar in an E2 reaction?
Why do the molecules have to be coplanar in an E2 reaction?
What is the preferred transition state geometry in E2 reactions?
What is the preferred transition state geometry in E2 reactions?
What is a syn coplanar transition state?
What is a syn coplanar transition state?
What is dehydration in organic chemistry?
What is dehydration in organic chemistry?
What type of reaction is acid-catalyzed dehydration of alcohols?
What type of reaction is acid-catalyzed dehydration of alcohols?
What do the temperature and concentration of acid required to dehydrate an alcohol depend on?
What do the temperature and concentration of acid required to dehydrate an alcohol depend on?
Which alcohols are the most difficult to dehydrate?
Which alcohols are the most difficult to dehydrate?
Which alcohols are easier to dehydrate?
Which alcohols are easier to dehydrate?
Which alcohols dehydrate most easily?
Which alcohols dehydrate most easily?
What is the order of ease for alcohols undergoing dehydration?
What is the order of ease for alcohols undergoing dehydration?
What happens when some 1° and 2° alcohols undergo dehydration?
What happens when some 1° and 2° alcohols undergo dehydration?
What type of reaction is the mechanism for dehydration of 2° and 3° alcohols?
What type of reaction is the mechanism for dehydration of 2° and 3° alcohols?
What is the order of stability of carbocations?
What is the order of stability of carbocations?
What is the slowest step in the dehydration of 2° and 3° alcohols?
What is the slowest step in the dehydration of 2° and 3° alcohols?
What describes the reactions where carbocations are formed from protonated alcohols?
What describes the reactions where carbocations are formed from protonated alcohols?
What stabilizes the transition state and also the carbocation?
What stabilizes the transition state and also the carbocation?
Why does the dehydration of 1° alcohols proceed through an E2 mechanism?
Why does the dehydration of 1° alcohols proceed through an E2 mechanism?
What mechanism does dehydration of a primary alcohol occur by?
What mechanism does dehydration of a primary alcohol occur by?
What is a methyl shift?
What is a methyl shift?
What is a 1,2 shift?
What is a 1,2 shift?
How does acid-catalyzed dehydration of alcohols follow Zaitsev's Rule?
How does acid-catalyzed dehydration of alcohols follow Zaitsev's Rule?
What is a hydride shift?
What is a hydride shift?
What is ring expansion?
What is ring expansion?
What is terminal alkyne acidity?
What is terminal alkyne acidity?
From what can alkynes be synthesized?
From what can alkynes be synthesized?
What are vicinal dihalides?
What are vicinal dihalides?
How can you form vicinal dibromide?
How can you form vicinal dibromide?
What is sodium amide NaNH2?
What is sodium amide NaNH2?
If the product of the dehydrohalogenation reactions is going to be an alkyne, how many molar equivalents of sodium amide are required?
If the product of the dehydrohalogenation reactions is going to be an alkyne, how many molar equivalents of sodium amide are required?
What is a geminal dihalide?
What is a geminal dihalide?
Geminal halides can be converted to alkynes by what process?
Geminal halides can be converted to alkynes by what process?
How can you turn ketones into alkynes?
How can you turn ketones into alkynes?
How can you remove the really really acidic H of a terminal alkyne?
How can you remove the really really acidic H of a terminal alkyne?
What are alkynide ions good for?
What are alkynide ions good for?
What does alkylation of alkynide ions illustrate?
What does alkylation of alkynide ions illustrate?
What is hydrogenation of alkenes?
What is hydrogenation of alkenes?
What is heterogeneous catalysis?
What is heterogeneous catalysis?
What is homogeneous catalysis?
What is homogeneous catalysis?
Catalytic hydrogenation reactions are a type of what?
Catalytic hydrogenation reactions are a type of what?
What are saturated compounds?
What are saturated compounds?
What are unsaturated compounds?
What are unsaturated compounds?
Unsaturated compounds can be _____ to saturated compounds by ______.
Unsaturated compounds can be _____ to saturated compounds by ______.
Even though hydrogenation is exothermic, why is a catalyst needed?
Even though hydrogenation is exothermic, why is a catalyst needed?
What type of addition reaction is catalytic hydrogenation?
What type of addition reaction is catalytic hydrogenation?
What is syn addition?
What is syn addition?
What is anti addition?
What is anti addition?
What is Lindlar's catalyst?
What is Lindlar's catalyst?
What is Lindlar's catalyst good for?
What is Lindlar's catalyst good for?
When does anti addition of hydrogen to the triple bond of alkynes occur?
When does anti addition of hydrogen to the triple bond of alkynes occur?
What is dissolving metal reduction?
What is dissolving metal reduction?
What does a dissolving metal reduction produce?
What does a dissolving metal reduction produce?
What does organic synthesis consist of?
What does organic synthesis consist of?
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Study Notes
The (E)-(Z) System
- Priority is determined by the groups attached to each carbon of a double bond.
- If the higher priority groups are on the same side of the double bond, the configuration is Z; if on opposite sides, it is E.
Definitions of Z and E
- Z (zusammen) means "together," indicating the higher priority groups are on the same side.
- E (entgegen) means "opposite," indicating the higher priority groups are on opposite sides.
Stability of Isomers
- Trans isomers of alkenes are generally more stable than cis isomers due to reduced steric strain from crowding.
Hydrogenation
- The addition of hydrogen to an alkene, categorized as an exothermic reaction.
Alkene Stability
- More substituted carbons in a double bond lead to increased stability of the alkene.
Cycloalkenes
- Cycloalkenes with up to five carbons must adopt a cis configuration.
Synthesis of Alkenes
- Key methods include elimination reactions, particularly the dehydrohalogenation of alkyl halides and dehydration of alcohols.
Conditions for Dehydrohalogenation
- Favorable conditions include using secondary or tertiary alkyl halides, bulky bases, strong, nonpolarizable bases, and high temperatures.
Zaitsev's Rule
- In eliminations, the major product tends to be the more stable, more highly substituted alkene.
Kinetics of Alkene Formation
- Kinetic control favors quicker product formation due to lower activation energy.
Mechanisms of Dehydration
- Primary alcohols usually undergo dehydration via an E2 mechanism, while secondary and tertiary alcohols typically follow an E1 mechanism.
Carbocation Stability
- The order of stability is tertiary > secondary > primary; methyl carbocations are the least stable.
Dehydration Temperature and Acidity
- Temperature and acid concentration for alcohol dehydration depend on the alcohol’s structure, with primary alcohols being most difficult to dehydrate.
Rearrangements during Dehydration
- Some primary and secondary alcohols may undergo carbon skeleton rearrangements during dehydration.
Shifts in Carbocations
- Methyl shifts and hydride shifts can stabilize carbocations by redistributing charge.
Terminal Alkyne Acidity
- Terminal alkynes have more acidic hydrogens than alkenes or alkanes, allowing for deprotonation with strong bases.
Alkyne Synthesis from Dihalides
- Vicinal dihalides and geminal dihalides can be converted to alkynes through dehydrohalogenation.
Use of Sodium Amide
- Sodium amide (NaNH2) acts as a strong base in the synthesis of alkynes, requiring three equivalents for alkyne formation.
Alkynide Ions
- Alkynide ions are effective nucleophiles for carbon-carbon bond formation, reacting with primary alkyl halides.
Catalytic Hydrogenation
- Hydrogenation of alkenes involves adding hydrogen across the double bond, typically using metal catalysts for reaction facilitation.
Addition Reactions
- Hydrogenation is categorized under syn addition, where added components are positioned on the same side.
Lindlar's Catalyst
- Used to selectively convert alkynes to cis-alkenes.
Dissolving Metal Reduction
- Results in anti addition to alkynes, generating E or trans-alkenes through radical mechanisms.
Organic Synthesis Types
- Involves reactions that either convert functional groups or generate new carbon-carbon bonds.
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