Organic Functional Groups and Their Reactions: Study Guide

Organic Functional Groups

Overview of Functional Groups

Organic chemistry involves a variety of functional groups, each with characteristic structures, naming conventions, and chemical reactivity. Understanding these groups is essential for predicting chemical behavior and reaction products.

• Alkanes: Saturated hydrocarbons with only single bonds.

• Alkenes: Unsaturated hydrocarbons containing at least one carbon-carbon double bond.

• Alkynes: Unsaturated hydrocarbons with at least one carbon-carbon triple bond.

• Aromatics: Compounds containing benzene rings (delocalized pi electrons).

• Phenols: Aromatic compounds with a hydroxyl group attached to the benzene ring.

• Alcohols: Compounds with a hydroxyl (-OH) group attached to a saturated carbon.

• Thiols: Compounds with a sulfhydryl (-SH) group.

• Ethers: Compounds with an oxygen atom connected to two alkyl or aryl groups.

• Aldehydes: Compounds with a carbonyl group (C=O) bonded to at least one hydrogen.

• Ketones: Compounds with a carbonyl group bonded to two carbon atoms.

• Carboxylic Acids: Compounds with a carboxyl group (-COOH).

• Esters: Derived from carboxylic acids and alcohols; contain -COOR group.

• Amines: Compounds with a nitrogen atom bonded to one or more alkyl or aryl groups.

• Amides: Compounds with a carbonyl group bonded to a nitrogen atom.

Classification of Amines and Alcohols

Amines and alcohols are classified based on the number of carbon-containing groups attached to the nitrogen or oxygen atom, respectively.

• Primary (1˚): Attached to one carbon group.

• Secondary (2˚): Attached to two carbon groups.

• Tertiary (3˚): Attached to three carbon groups.

Example: Ethanol (CH3CH2OH) is a primary alcohol; dimethylamine (CH3NHCH3) is a secondary amine.

Reactions of Functional Groups

Alkenes and Alkynes

Alkenes and alkynes undergo characteristic addition and combustion reactions.

• Hydrogenation: Addition of H2 across double or triple bonds to form alkanes. $\ce{RCH=CH2 + H2 ->[Pt] RCH2CH3}$

• Hydration: Addition of water (H2O) to form alcohols. $\ce{RCH=CH2 + H2O ->[H^+] RCH(OH)CH3}$

• Combustion: Complete oxidation to CO2 and H2O. $\ce{C_nH_{2n} + (3n/2)O2 -> nCO2 + nH2O}$

Example: Ethene reacts with hydrogen to form ethane.

Reactions of Alcohols

• Dehydration: Removal of water to form alkenes. $\ce{RCH2CH2OH ->[H^+, \Delta] RCH=CH2 + H2O}$

• Oxidation: Primary alcohols oxidize to aldehydes, then to carboxylic acids; secondary alcohols to ketones. $\ce{RCH2OH ->[O] RCHO ->[O] RCOOH}$ (primary) $\ce{R2CHOH ->[O] R2CO}$ (secondary)

Example: Ethanol oxidizes to acetaldehyde, then to acetic acid.

Reactions of Thiols

• Oxidation: Two thiol molecules form a disulfide bond. $\ce{2RSH ->[O] RSSR + 2H^+ + 2e^-}$

Example: Cysteine residues in proteins form disulfide bridges.

Aldehydes and Ketones

• Oxidation: Aldehydes oxidize to carboxylic acids; ketones generally do not oxidize further. $\ce{RCHO ->[O] RCOOH}$

• Reduction: Both can be reduced to alcohols. $\ce{RCHO + H2 ->[Pt] RCH2OH}$ (aldehyde) $\ce{RCOR' + H2 ->[Pt] RCH(OH)R'}$ (ketone)

Example: Acetone reduces to isopropanol.

Carboxylic Acids

• Deprotonation: Carboxylic acids lose a proton to form carboxylate ions. $\ce{RCOOH + H2O <=> RCOO^- + H3O^+}$

• Neutralization: Reaction with bases to form salts and water. $\ce{RCOOH + NaOH -> RCOONa + H2O}$

• Esterification: Reaction with alcohols to form esters and water. $\ce{RCOOH + R'OH <=>[H^+] RCOOR' + H2O}$

Example: Acetic acid reacts with ethanol to form ethyl acetate.

Esters

• Acid Hydrolysis: Esters react with water and acid to form carboxylic acids and alcohols. $\ce{RCOOR' + H2O ->[H^+] RCOOH + R'OH}$

• Base Hydrolysis (Saponification): Esters react with base to form carboxylate salts and alcohols. $\ce{RCOOR' + NaOH -> RCOONa + R'OH}$

Example: Methyl acetate hydrolyzes to acetic acid and methanol.

Amines

• Alkylammonium Formation: Amines react with water or acids to form alkylammonium ions. $\ce{RNH2 + H2O <=> RNH3^+ + OH^-}$ $\ce{RNH2 + HCl -> RNH3^+Cl^-}$

• Neutralization: Amines react with acids to form ammonium salts. $\ce{RNH2 + H^+ -> RNH3^+}$

• Amine Formation via Alkylammonium: Alkylammonium ions can be converted back to amines by base.

• Amide Formation: Amines react with carboxylic acids to form amides and water. $\ce{RCOOH + R'NH2 -> RCONHR' + H2O}$

Example: Methylamine reacts with acetic acid to form acetamide.

Amides

• Acid Hydrolysis: Amides react with acid and water to form carboxylic acids and ammonium ions. $\ce{RCONH2 + H2O + H^+ -> RCOOH + NH4^+}$

• Base Hydrolysis: Amides react with base to form carboxylate ions and ammonia. $\ce{RCONH2 + NaOH -> RCOO^-Na^+ + NH3}$

Example: Acetamide hydrolyzes to acetic acid and ammonia.

Summary Table: Functional Groups and Key Reactions

Functional Group	Key Reactions	Example Product
Alkene/Alkyne	Hydrogenation, Hydration, Combustion	Alkane, Alcohol, CO2 + H2O
Alcohol	Dehydration, Oxidation	Alkene, Aldehyde/Ketone
Thiol	Oxidation	Disulfide
Aldehyde/Ketone	Oxidation, Reduction	Carboxylic Acid, Alcohol
Carboxylic Acid	Deprotonation, Neutralization, Esterification	Carboxylate, Salt, Ester
Ester	Acid/Base Hydrolysis	Carboxylic Acid, Alcohol, Carboxylate
Amine	Alkylammonium Formation, Neutralization, Amide Formation	Ammonium Salt, Amide
Amide	Acid/Base Hydrolysis	Carboxylic Acid, Ammonia

Additional info: For thiols, nomenclature is not required; focus on structure and oxidation. For all other groups, be able to draw, name, and predict products of key reactions as outlined above.