Organic Chemistry Functional Groups

Overview

This lecture covers the most common organic chemistry functional groups, their structures, naming conventions, and examples essential for understanding and identifying them.

Alkanes, Alkenes, and Alkynes

• Alkanes are hydrocarbons with only carbon–hydrogen single bonds and end in “-ane.”
• Alkane examples: methane (1 C), ethane (2 C), propane (3 C), butane (4 C), pentane (5 C), etc.
• Alkenes have at least one carbon–carbon double bond; named with “-ene” and lowest double bond position.
• Alkynes have at least one carbon–carbon triple bond; named with “-yne” and lowest triple bond position.

Cyclic and Aromatic Compounds

• Cycloalkanes are ring structures of alkanes, e.g., cyclopentane (5 C), cyclohexane (6 C).
• Aromatic rings have conjugated double bonds; benzene is the most common example.

Halogenated Compounds & Ethers

• Alkyl halides (haloalkanes) have a halogen (X = Cl, Br, F, I) attached to a hydrocarbon (RX).
• Ethers have an oxygen atom connected to two alkyl groups (R–O–R); named by alkyl groups, e.g., dimethyl ether.

Alcohols, Ketones, and Aldehydes

• Alcohols contain an –OH group on a carbon; named by position (e.g., 1-butanol or 2-butanol).
• Ketones have a carbonyl (C=O) group between two carbons (R–CO–R); e.g., 2-pentanone.
• Aldehydes have a terminal carbonyl (R–CHO); always at chain end and named with “-al,” e.g., hexanal.

Carboxylic Acid Derivatives

• Carboxylic acids have a –COOH group; named with “-oic acid,” e.g., hexanoic acid.
• Esters have R–COO–R′ structure; named “alkyl alkanoate,” e.g., methyl ethanoate.
• Amides have R–CONH₂ structure; named by replacing “-e” with “-amide,” e.g., butanamide.
• Nitriles feature C≡N bond; named with “-nitrile,” e.g., ethanenitrile.
• Acid anhydrides (R–CO–O–CO–R) and acid chlorides (R–COCl) are carboxylic acid derivatives.
• Acid bromides substitute Cl with Br in acid chlorides.

Sulfur-containing Compounds

• Thiols have –SH group, analogous to alcohols; named with “thiol.”
• Thioethers (R–S–R) are similar to ethers with sulfur replacing oxygen.
• Thioesters are analogs of esters but with sulfur.

Unique & Mixed Functional Groups

• Enol: alcohol (–OH) group directly attached to a carbon–carbon double bond.
• Enamine: nitrogen bonded to an alkene carbon, two R groups on nitrogen.
• Imine: carbon double-bonded to a nitrogen atom (C=N).

Peroxides, Peroxy Acids & Nitro

• Peroxides: two oxygens bonded together (–O–O–).
• Peroxy acids: combination of carboxylic acid and peroxide.
• Nitro groups: contain –NO₂ attached to carbon.

Ions & Other Species

• Carbocation: positively charged carbon atom.
• Radical: carbon with an unpaired electron.
• Carbanion: negatively charged carbon atom.
• Carbene: neutral carbon species with two non-bonded electrons.

Key Terms & Definitions

• Alkane — hydrocarbon with only single bonds.
• Alkene — hydrocarbon with at least one double bond.
• Alkyne — hydrocarbon with at least one triple bond.
• Cycloalkane — ring-shaped alkane.
• Aromatic — ring with alternating double bonds (e.g., benzene).
• Alkyl halide — hydrocarbon with halogen substituent.
• Ether — molecule with R–O–R structure.
• Alcohol — molecule with an –OH group.
• Ketone — carbonyl group bonded to two carbons.
• Aldehyde — terminal carbonyl group.
• Carboxylic acid — –COOH functional group.
• Ester — R–COO–R structure.
• Amide — R–CONH₂ group.
• Nitrile — C≡N functional group.
• Acid anhydride — two acyl groups bonded to an oxygen.
• Acid chloride/bromide — acyl group with Cl/Br.
• Thiol — –SH group.
• Thioether — R–S–R structure.
• Enol — –OH on alkene carbon.
• Enamine — nitrogen attached to alkene.
• Imine — C=N double bond.
• Peroxide — –O–O– bond.
• Peroxy acid — carboxylic acid with peroxide.
• Nitro group — –NO₂ group.
• Carbocation — positively charged carbon.
• Radical — carbon with unpaired electron.
• Carbanion — negatively charged carbon.
• Carbene — neutral divalent carbon.

Action Items / Next Steps

• Review the structures and naming conventions for each functional group.
• Practice drawing and identifying functional groups in organic molecules.
• Prepare for quiz/exam by memorizing key functional group characteristics and suffixes.