Orgo 2 Wittig reaction flashcards

What is the Wittig reaction?

A chemical reaction that converts carbonyl compounds into alkenes using phosphonium ylides.

Wittig reaction mechanism involves which key step?

Formation of a four-membered ring intermediate called an oxaphosphetane.

True or False: The Wittig reaction can only form Z-alkenes.

False. It can produce both E- and Z-alkenes depending on the ylide used.

Fill in the blank: The Wittig reaction uses __________ to generate alkenes.

Phosphonium ylides.

Compare E-alkenes and Z-alkenes in the context of the Wittig reaction.

- E-alkenes: Trans configuration, generally more stable. - Z-alkenes: Cis configuration, often less stable.

What types of carbonyl compounds can participate in the Wittig reaction?

Aldehydes and ketones are the primary carbonyl compounds used.

What is a phosphonium ylide?

A compound formed by the reaction of a phosphonium salt with a strong base, containing a positively charged phosphorus and a negatively charged carbon.

True or False: The stereochemistry of the starting material always dictates the stereochemistry of the product.

False. The stereochemistry of the ylide can lead to different alkene configurations.

What role does the base play in the Wittig reaction?

The base deprotonates the phosphonium salt to generate the ylide, which is essential for the reaction.

Example: Write a simple reaction equation for a Wittig reaction.

RCHO + Ph3P=CH2 → RCH=CHPh + Ph3PO

What is the purpose of using a stabilizing group in ylides?

Stabilizing groups enhance the reactivity and selectivity of the ylide, affecting the outcome of the reaction.

List key features of the oxaphosphetane intermediate.

- Formed during the Wittig reaction - Contains a phosphorus atom - Isomerizes to produce the alkene

Cause → Effect: Why are Wittig reactions valuable in organic synthesis?

They allow for the formation of specific alkenes, facilitating the construction of complex molecules.

What are common solvents used in the Wittig reaction?

Common solvents include dichloromethane (DCM), tetrahydrofuran (THF), and benzene.

True or False: The Wittig reaction is limited to non-polar solvents.

False. The reaction can occur in a variety of solvents depending on the desired outcome.

What is the significance of the ylide's structure?

The structure determines the nucleophilicity and stability, which influence the reaction's regioselectivity and stereochemistry.

What is a common phosphonium salt used in the Wittig reaction?

Methyltriphenylphosphonium bromide (MePPh₃Br) is a common phosphonium salt.

True or False: Strong bases are always required in the Wittig reaction.

False. While strong bases like n-BuLi are common, milder bases like NaH can also be used.

Fill in the blank: The typical base used in the Wittig reaction is _______.

n-Butyllithium (n-BuLi) is often used.

How does temperature affect the Wittig reaction?

Increased temperature can favor product formation but may lead to side reactions.

Compare n-BuLi and NaH as bases in Wittig reactions.

n-BuLi is stronger, leading to faster reactions; NaH is milder, better for sensitive substrates.

What type of solvent is preferred for Wittig reactions?

Polar aprotic solvents like DMF or DMSO are preferred for better solubility.

List two modifications to improve Wittig reaction yields.

- Use of higher concentrations - Employing microwave irradiation to speed up reactions.

What is the role of the reagent triphenylphosphine (PPh₃)?

PPh₃ stabilizes the phosphonium salt and facilitates the nucleophilic attack on the carbonyl.

True or False: Wittig reactions can only produce alkenes.

True. The primary product of a Wittig reaction is an alkene.

What can be used to protect sensitive functional groups during the reaction?

Protecting groups like TMS (trimethylsilyl) can be employed to safeguard groups.

What happens when the wrong base is used in the Wittig reaction?

Using an inappropriate base can lead to poor yields or completely inhibit the reaction.

Which phosphonium salt often leads to E/Z stereochemistry control?

Using specific phosphonium salts can favor the formation of E or Z alkenes based on sterics.

What is a major application of the Wittig reaction?

Synthesis of alkenes from aldehydes or ketones, facilitating complex organic synthesis.

True or False: The Wittig reaction can only synthesize linear alkenes.

False. It can synthesize branched and cyclic alkenes.

Fill in the blank: The Wittig reaction is commonly used in the synthesis of __________.

pharmaceuticals, agrochemicals, and natural products.

What type of compounds can be synthesized using the Wittig reaction?

Alkenes from carbonyl compounds like aldehydes and ketones.

Cause → Effect: Why is the Wittig reaction important in organic synthesis?

It creates carbon-carbon double bonds, enabling the formation of complex molecules.

Compare the Wittig reaction to traditional alkene synthesis methods.

Wittig is more selective and can form alkenes with specific stereochemistry.

What is a real-world example of Wittig reaction application?

Synthesis of vitamin A derivatives using the Wittig reaction to form crucial double bonds.

Fill in the blank: The Wittig reaction can help in creating __________ used in perfumes.

aldehydes and ketones.

True or False: The Wittig reaction is limited to laboratory use only.

False. It is applied in industrial settings for large-scale syntheses.

What is a key benefit of the Wittig reaction in synthesis?

It allows for the creation of alkenes without rearrangement of the carbon skeleton.

Give a short example of a compound synthesized via Wittig reaction.

Synthesis of stilbene from benzaldehyde and a phosphonium ylide.

What type of ylide is often used in the Wittig reaction?

Stabilized ylides, which can produce alkenes with better selectivity.