Study Guide: Ethers, Epoxides, Aldehydes, Ketones, and Carboxylic Acids

Chapter 17: Chemistry of Ethers, Epoxides, and Sulfides

Ether Nomenclature

Ethers are organic compounds containing an oxygen atom connected to two alkyl or aryl groups. Their nomenclature follows two main systems:

• Functional (IUPAC) Nomenclature: The ether is named as an alkoxy substituent on the main chain. For example, methoxyethane for CH3OCH2CH3.

• Substitutive (Common) Nomenclature: The names of the two groups attached to oxygen are listed alphabetically, followed by the word "ether" (e.g., ethyl methyl ether).

Common Names for Cyclic Ethers

• Oxirane: The simplest epoxide (three-membered cyclic ether).

• THF (Tetrahydrofuran): A five-membered cyclic ether commonly used as a solvent.

Alcohol Condensation (Intramolecular Etherification)

Alcohols can undergo condensation reactions to form ethers, especially under acidic conditions. When both hydroxyl groups are in the same molecule, intramolecular etherification yields cyclic ethers.

• General Reaction: $2\ \mathrm{ROH}\ \xrightarrow{\text{acid}}\ \mathrm{R-O-R}\ +\ \mathrm{H_2O}$

Williamson Ether Synthesis

The Williamson ether synthesis is a key method for preparing ethers by reacting an alkoxide ion with a primary alkyl halide.

• General Reaction: $\mathrm{R-O^-}\ +\ \mathrm{R'-X}\ \rightarrow\ \mathrm{R-O-R'}\ +\ \mathrm{X^-}$

• Reactivity: Primary alkyl halides are most suitable; secondary and tertiary halides may lead to elimination.

Cleavage of Ethers by Hydrogen Halides (HX)

Ethers can be cleaved by strong acids such as HI or HBr, producing alkyl halides and alcohols or two alkyl halides.

• General Reaction: $\mathrm{R-O-R'}\ +\ \mathrm{HX}\ \rightarrow\ \mathrm{R-X}\ +\ \mathrm{R'-OH}$

Epoxide Nomenclature

• Epoxides are named as alkene oxides (e.g., ethylene oxide) or as epoxy substituents on the parent chain (e.g., 1,2-epoxypropane).

Epoxide Formation

• From Alkenes with Peroxycarboxylic Acid: $\mathrm{Alkene}\ +\ \mathrm{RCO_3H}\ \rightarrow\ \mathrm{Epoxide}\ +\ \mathrm{RCO_2H}$

• Via Halohydrin Formation: Alkene reacts with X2/H2O to form a vicinal halohydrin, which cyclizes under base to give an epoxide.

Epoxide Ring Opening (Acidic and Basic Conditions)

• Acidic Conditions: Nucleophile attacks the more substituted carbon.

• Basic Conditions: Nucleophile attacks the less hindered (less substituted) carbon.

Spectroscopy of Ethers and Epoxides

• IR Spectroscopy: C–O stretch appears around 1050–1150 cm–1.

• NMR Spectroscopy: Protons adjacent to oxygen appear downfield (3.3–4.0 ppm).

Chapter 18: Chemistry of Carbonyl Compounds (Aldehydes and Ketones)

Nomenclature and Reactivity

• Aldehydes: Named by replacing the -e of the parent alkane with -al (e.g., ethanal).

• Ketones: Named by replacing -e with -one (e.g., propanone).

• Reactivity Order: Aldehydes > Ketones > Alcohols (thiols) > Alkenes > Alkynes > Alkanes = Halogens = Alkoxides.

Hydration, Acetal, and Hemiacetal Formation

• Hydration: Aldehydes and ketones react with water to form geminal diols.

• Acetal/Hemiacetal Formation: Reaction with alcohols forms hemiacetals (one equivalent) and acetals (two equivalents).

• Cyclic Acetals: Formed when diols react with carbonyl compounds.

Cyanohydrin Formation

• Aldehydes and ketones react with HCN to form cyanohydrins.

• General Reaction: $\mathrm{R_2C=O}\ +\ \mathrm{HCN}\ \rightarrow\ \mathrm{R_2C(OH)CN}$

Spectroscopy of Aldehydes and Ketones

• IR: C=O stretch at 1720–1740 cm–1 (aldehydes slightly higher than ketones).

• NMR: Aldehyde protons appear at 9–10 ppm.

Imine and Enamine Formation

• Imine: Formed by reaction of a primary amine with a carbonyl compound.

• Enamine: Formed by reaction of a secondary amine with a carbonyl compound.

Wittig Reaction

• Converts aldehydes or ketones to alkenes using a phosphonium ylide.

• General Reaction: $\mathrm{R_2C=O}\ +\ \mathrm{Ph_3P=CHR'}\ \rightarrow\ \mathrm{R_2C=CHR'}\ +\ \mathrm{Ph_3P=O}$

Baeyer-Villiger Reaction

• Oxidation of ketones (or aldehydes) to esters (or carboxylic acids) using peroxyacids.

Chromic Acid Oxidation

• Strong oxidant for converting primary alcohols to carboxylic acids and secondary alcohols to ketones.

Chapter 19: Chemistry of Carboxylic Acids

Nomenclature

• Named by replacing the -e of the parent alkane with -oic acid (e.g., ethanoic acid).

Physical Properties: pKa, Boiling Point, and Solubility

• pKa: Carboxylic acids are more acidic than alcohols.

• Boiling Point: Higher than alcohols due to hydrogen bonding and dimer formation.

• Solubility: Small carboxylic acids are soluble in water; solubility decreases with increasing chain length.

Acid Strength Comparisons

• Electron-withdrawing groups increase acidity; electron-donating groups decrease acidity.

Henderson-Hasselbalch Equation

• Relates pH, pKa, and the ratio of conjugate base to acid:

$\mathrm{pH} = \mathrm{p}K_a + \log\left(\frac{[A^-]}{[HA]}\right)$

Oxidation Reactions to Form Carboxylic Acids

• From Alcohols: Primary alcohols oxidized to carboxylic acids (e.g., using chromic acid or permanganate).

• From Benzylic Carbons: Side chains on aromatic rings oxidized to benzoic acid.

• From Aldehydes: Aldehydes oxidized to carboxylic acids.

• Chromic Acid vs Permanganate: Both are strong oxidants; permanganate often requires acidic workup.

Fischer Esterification and Intramolecular Esterification

• Fischer Esterification: Carboxylic acid reacts with alcohol under acid catalysis to form an ester.

• Intramolecular Esterification: Formation of lactones (cyclic esters) from hydroxy acids.

CO2 and CN as Inorganic Sources of Carboxylic Acids

• Carboxylation of Grignard reagents with CO2 forms carboxylic acids.

• Nitriles (from CN–) hydrolyzed to carboxylic acids.

Reduction of Carboxylic Acids to Alcohols

• Carboxylic acids can be reduced to primary alcohols using strong reducing agents (e.g., LiAlH4).

Decarboxylation

• Loss of CO2 from carboxylic acids, often facilitated by heat or specific functional groups (e.g., β-keto acids).

Spectroscopy of Carboxylic Acids

• IR: Broad O–H stretch (2500–3300 cm–1), C=O stretch (1700–1725 cm–1).

• NMR: Carboxylic acid proton appears at 10–13 ppm.

Table: Comparison of Physical Properties

Compound Type	pKa	Boiling Point	Water Solubility
Alcohol	~16	Lower	High (small alcohols)
Carboxylic Acid	~5	Higher	High (small acids)

Additional info: Table values are typical for simple alcohols and carboxylic acids; actual values depend on molecular structure.