Organic Functional Groups Overview

Overview

This lecture introduces the most important functional groups in organic chemistry, focusing on their structures, properties, and relevance for typical course content.

Introduction to Functional Groups

• Functional groups are specific atom arrangements in molecules that give characteristic properties and reactions.
• About 15–25 key functional groups cover most needs in introductory organic chemistry.
• Understanding names and connecting them to structures is crucial for learning organic chemistry.

Hydrocarbon Functional Groups

• Alkanes: Only single bonds; very non-polar, low boiling points, sp³ hybridized carbons.
• Alkenes: Contain at least one C=C double bond; sp² hybridized, trigonal planar geometry.
• Alkynes: Contain at least one C≡C triple bond; sp hybridized, linear geometry.
• Aromatic rings: Six-membered rings with delocalized electrons (e.g., benzene); unusually stable, sp² hybridized.

Polar Functional Groups: Alcohols, Ethers, Amines, Thiols, Alkyl Halides

• Alcohols: R–OH group; capable of hydrogen bonding, weak acids and Lewis bases.
• Ethers: R–O–R'; can’t hydrogen bond as donors, moderate polarity, common solvents.
• Amines: R–NH₂, R–NHR', or R–NR'₂; basic due to nitrogen lone pair; some can hydrogen bond.
• Thiols: R–SH; structurally related to alcohols, more acidic, strong odors.
• Alkyl halides: R–X (X = F, Cl, Br, I); higher boiling points than alkanes due to dipole-dipole interactions.

Carbonyl-Based Functional Groups: Aldehydes, Ketones, Carboxylic Acids, Esters

• Carbonyl group (C=O) is polar with partial positive carbon.
• Aldehydes: R–CHO; C=O bonded to at least one H.
• Ketones: R₂C=O; C=O bonded to two carbons.
• Carboxylic acids: R–COOH; carbonyl bonded to hydroxyl, weak acids, hydrogen bonding.
• Esters: R–COOR'; like acids but O–H replaced by O–C, often have sweet smells.

Carboxylic Acid Derivatives: Amides, Acid Halides, Anhydrides, Nitriles

• Amides: Carbonyl bonded to nitrogen; important in peptides; can hydrogen bond if N–H is present.
• Acid halides: Carbonyl with –Cl, –Br, –I, or –F replacing –OH.
• Anhydrides: Two carbonyls bonded to the same oxygen; formed from carboxylic acids.
• Nitriles: R–C≡N; strongly polar, can be derived from amides.

Miscellaneous Functional Groups

• Epoxides: Three-membered cyclic ethers, reactive due to ring strain.
• Thioethers: R–S–R' (sulfides); sulfur analogs of ethers.
• Nitro groups: R–NO₂, strongly electron-withdrawing.
• Imines: C=N in place of the carbonyl oxygen; nitrogen analogs of aldehyde/ketone.
• Azides: R–N₃; common in organic synthesis.

Key Terms & Definitions

• Functional group — a specific grouping of atoms that determines the chemical behavior of the molecule.
• Alkane — hydrocarbon with only single bonds.
• Alkene — hydrocarbon with at least one double bond.
• Alkyne — hydrocarbon with at least one triple bond.
• Aromatic ring — a stable, cyclic, conjugated ring system (ex: benzene).
• Alcohol — contains a hydroxyl (–OH) group.
• Ether — contains an oxygen bonded to two carbons (R–O–R').
• Amine — contains nitrogen with single bonds to carbon and/or hydrogen.
• Thiol — contains an –SH group.
• Carbonyl group — a C=O double bond.
• Aldehyde — carbonyl attached to at least one hydrogen.
• Ketone — carbonyl attached to two carbons.
• Carboxylic acid — carbonyl attached to –OH group.
• Ester — carbonyl attached to an –OR group.
• Amide — carbonyl attached to a nitrogen atom.
• Nitrile — carbon triple-bonded to nitrogen (–C≡N).

Action Items / Next Steps

• Draw and memorize the structures of each functional group listed above.
• Practice identifying functional groups in sample molecules.
• Review the table of functional group priorities for nomenclature.
• Read advanced articles on electronegativity and resonance for deeper understanding.