MEDCHEM 11 Notes

These flashcards cover key concepts related to aldehydes and ketones in medicinal and pharmaceutical chemistry, including their structures, reactivity, mechanisms, and reactions.

What are the general structures of aldehydes and ketones?

Aldehydes have the functional group -CHO, while ketones have the functional group -C(=O)-R, where R can be an alkyl or aryl group.

What is the polarity of the carbonyl group?

The carbonyl group (C=O) is polar due to the difference in electronegativity between carbon and oxygen.

Which is generally more reactive toward nucleophiles, aldehydes or ketones?

Aldehydes are generally more reactive toward nucleophiles than ketones.

What is formed when an aldehyde reacts with an alcohol in the presence of an acid catalyst?

A hemiacetal is formed.

What types of nucleophiles react with carbonyl compounds?

Both oxygen nucleophiles (e.g., alcohols) and nitrogen nucleophiles (e.g., amines) can react with carbonyl compounds.

What is the characteristic structure of a ketone?

Ketones have a carbonyl group with two alkyl or aryl groups attached to the carbonyl carbon.

What is the significance of the carbonyl carbon's geometry?

The carbonyl carbon has trigonal planar geometry with bond angles around 120 degrees, influencing its reactivity.

Explain why carbonyl compounds have weak acidity.

Hydrogens on the alpha-carbon of carbonyl compounds are slightly acidic due to the polar C=O group.

What role does acid catalysis play in nucleophilic addition reactions?

Acid catalysis increases the electrophilicity of the carbonyl group, enhancing reaction rates.

What is a hemiacetal?

A hemiacetal has one ether and one alcohol functional group on the same carbon.

How is an acetal formed from a hemiacetal?

An acetal is formed from a hemiacetal in the presence of excess alcohol.

What is the role of hydroxylamine in reactions with carbonyl compounds?

Hydroxylamine acts as a nitrogen nucleophile to form oximes from carbonyl compounds.

What are the products when an aldehyde reacts with a hydrazine?

A hydrazone is formed when an aldehyde reacts with a hydrazine.

How do steric factors influence the reactivity of ketones compared to aldehydes?

Steric hindrance in ketones due to larger substituents makes them less reactive than aldehydes.

What happens during the nucleophilic addition of alcohol to a carbonyl compound?

The nucleophile (alcohol) adds to the electrophilic carbon of the carbonyl, forming a hemiacetal.

Describe the general mechanism of hemiacetal formation.

The mechanism includes protonation of the carbonyl, nucleophilic addition of alcohol, and formation of a hemiacetal.

What is a Schiff base?

A Schiff base is an imine formed when an aldehyde reacts with an amine.

What is the effect of electron-donating groups on the reactivity of carbonyl compounds?

Electron-donating groups decrease the electrophilicity of the carbonyl carbon, making it less reactive.

What type of reaction occurs when acetal formation is catalyzed by an acid?

Acetal formation is a condensation reaction, which involves elimination of water.

Can glucose form hemiacetals?

Yes, glucose can form cyclic hemiacetals due to its structure with both aldehyde and alcohol groups.

How do nitrogen nucleophiles react with carbonyl compounds?

Nitrogen nucleophiles can react to form imines or oximes depending on the reagent used.

What happens to hemiacetals in the presence of excess alcohol?

Hemiacetals can be converted to acetals when treated with excess alcohol.

What is a general characteristic of nucleophiles in relation to carbonyl compounds?

Nucleophiles attack the electrophilic carbon of the carbonyl group during reactions.

Why are aldehydes typically more reactive than ketones for steric reasons?

Aldehydes have less steric hindrance compared to ketones due to their structure.

What is the outcome when a carbonyl compound reacts with amines?

The outcome is the formation of an imine.

What structural feature distinguishes an oxime from an imine?

An oxime contains a hydroxyl (OH) group bonded to the nitrogen, while an imine does not.

What is the role of an acid catalyst in the reaction of carbonyl compounds with alcohol?

An acid catalyst increases the reactivity of the carbonyl compound by enhancing electrophilicity.

What type of compounds can be classified as carbonyl compounds?

Aldehydes and ketones are examples of carbonyl compounds.

How does the relative acidity of alpha-hydrogens influence carbonyl chemistry?

Alpha-hydrogens can participate in reactions that involve base catalysis due to their weak acidity.

What defines the functionality of a ketone?

A ketone is characterized by having a carbonyl group flanked by two carbon atoms.

In terms of connection to the carbon chain, how are aldehydes defined?

Aldehydes are connected to at least one hydrogen atom at the carbonyl carbon.

What is the electrophilicity of the carbonyl carbon influenced by?

Electrophilicity is influenced by the polarity of the carbonyl group and surrounding substituents.

What type of reaction products can be formed from nucleophilic attack on carbonyls?

Products can include hemiacetals, acetals, imines, and oximes.

What does an increase in acidity do to the electrophilicity of a carbonyl?

Increased acidity enhances the electrophilicity of the carbonyl and facilitates nucleophilic attack.

What is the typical bond angle around the carbonyl carbon?

The typical bond angle is approximately 120 degrees.

Who typically provides information on the reactivity and mechanisms involving aldehydes and ketones?

Prof. Marc Devocelle conveys this information in lectures on Medicinal & Pharmaceutical Chemistry.

What are the natural sources of aldehydes and ketones mentioned?

Examples include 11-cis-retinal and 4-(4-hydroxyphenyl)butan-2-one found in nature.

What is a common use of methanal?

Methanal (formaldehyde) is commonly used as a preservative in a 37% aqueous solution.

How are ketones distinguished structurally from aldehydes?

Ketones have two carbon groups attached to the carbonyl carbon; aldehydes have one.

What is the major driving force for the reactions of carbonyl compounds?

The polar nature of the carbonyl group provides a strong electrophilic center for nucleophilic attack.