Unit 4 — Carbonyl Compounds (Aldehydes & Ketones) — Study Notes Summary & Study Notes

🧪 Introduction — Carbonyl Compounds

Carbonyl group: a functional group with a double bond between carbon and oxygen, written as $C=O$. This group is the defining feature of aldehydes and ketones and strongly influences their reactivity.

Aldehydes vs Ketones: In aldehydes the carbonyl carbon is at the end of the chain and carries at least one hydrogen, represented as the formyl group $-CHO$. In ketones the carbonyl carbon is bonded to two carbon groups (alkyl $R$ or aryl $Ar$): generally written as $R-CO-R'$.

🔬 Structure & Key Properties

• Polarity: The $C=O$ bond is polar (oxygen is more electronegative), making the carbonyl carbon electrophilic and susceptible to nucleophilic attack.
• Reactivity: Both classes undergo nucleophilic addition at the carbonyl carbon. Aldehydes are typically more reactive than ketones toward nucleophiles because they have fewer electron-donating alkyl groups and less steric hindrance.
• Oxidation: Aldehydes can be oxidized to carboxylic acids; ketones are generally resistant to mild oxidation.

🧾 Nomenclature — Aldehydes (from image content)

Common names: Often derived from the corresponding carboxylic acid by replacing the acid ending with an aldehyde name. Examples:

• Formaldehyde: oxidizes to formic acid.
• Acetaldehyde: oxidizes to acetic acid.
• Benzaldehyde: oxidizes to benzoic acid.

IUPAC names: Select the longest chain containing the aldehyde. Replace the terminal alkane "-e" ending with "-al". The aldehyde carbon is always carbon-1 (the functional group is terminal), so no locant is needed for the carbonyl position in a simple chain.

⚙️ Practical notes & applications

• Uses: Aldehydes and ketones are important in organic synthesis, pharmaceuticals, fragrances, and biological systems.
• Identification: Aldehydes often give positive tests with mild oxidizing agents (e.g., Tollens or Fehling tests) while ketones usually do not.

✳️ Quick summary

• Carbonyl = $C=O$; aldehyde = $-CHO$ (terminal); ketone = internal $C=O$ between two carbons.
• Aldehydes: more reactive to nucleophiles, oxidizable to acids.
• Nomenclature: common names from acids; IUPAC ends with -al and assigns the aldehyde carbon as C-1.

📝 Supplementary Notes (Text Input)

Core concepts: Remember that the behavior of carbonyl compounds stems from the polarized $C=O$ bond. The partial positive charge on carbon makes it a target for nucleophiles, while the oxygen can stabilize negative charge through resonance and induction.

Mnemonic: "Aldehyde = At the end (A)" helps recall the terminal position ($-CHO$) and that it is readily oxidized.

Naming tip: When naming an aldehyde by IUPAC, always choose the longest chain that contains the aldehyde carbon; replace the alkane suffix with -al and number from the aldehyde end so the carbonyl is C-1.

Short practical reminder: Aldehydes often give positive Tollens/Fehling results; ketones usually do not — a useful diagnostic in the lab.