Comprehensive Study Notes on Alcohols, Ethers, Aldehydes, Ketones, Carboxylic Acids, and Esters

Introduction to Oxygen-Containing Functional Groups

• Organic compounds are classified based on their functional groups to organize the vast number of molecules and predict their reactions.
• This study guide focuses on oxygenated hydrocarbons, which include:
  • Alcohols
  • Ethers
  • Aldehydes
  • Ketones
  • Carboxylic Acids
  • Esters (including fats and oils)
• Many of these compounds are found in nature, such as in fruits, flowers, and medicinal plants, and have significant industrial and pharmaceutical applications.

Alcohols: Classification and Nomenclature

• Definition: Alcohols are derivatives of hydrocarbons where one or more hydrogen atoms are replaced by a hydroxyl group ($-OH$).

• Functional Group: The hydroxyl group ($-OH$) is directly attached to the carbon atom(s) of an aliphatic system.

• General Classification:

  • Monohydric: Contain one $-OH$ group ($\text{e.g., Ethanol, } CH_3-CH_2-OH$).
  • Dihydric (Glycols/Diols): Contain two $-OH$ groups ($\text{e.g., Ethane-1,2-diol, } H_2C(OH)-CH_2(OH)$).
  • Trihydric: Contain three $-OH$ groups ($\text{e.g., Propane-1,2,3-triol or Glycerol, } H_2C(OH)-CH(OH)-CH_2(OH)$).
  • Polyhydric: Contain many hydroxyl groups.

• Classification of Monohydric Alcohols:

  • Primary (1°): The carbon with the $-OH$ group is attached to only one alkyl group ($R-CH_2-OH$).
  • Secondary (2°): The carbon with the $-OH$ group is attached to two alkyl groups ($R_2CH-OH$).
  • Tertiary (3°): The carbon with the $-OH$ group is attached to three alkyl groups ($R_3C-OH$).

• Nomenclature:

  • Common System: Write the name of the alkyl group followed by the word "alcohol" ($\text{e.g., methyl alcohol}$).
  • IUPAC System: Replace the terminal "-e" of the parent alkane with "-ol." For chains with three or more carbons, numbering starts from the end closest to the hydroxyl group ($\text{e.g., 2-propanol}$).
  • For polyhydric alcohols: The "e" of the alkane is retained, and prefixes like "di," "tri," etc., are added before "-ol" ($\text{e.g., 1,2-ethanediol}$).

Physical Properties of Alcohols

• Polarity: The hydroxyl group is polar due to the high electronegativity of oxygen.
• Hydrogen Bonding: Significant hydrogen bonding occurs between alcohol molecules, leading to higher melting and boiling points compared to hydrocarbons of similar molecular mass.
• Physical Constants (First Six Monohydric Alcohols):
  • Methanol: $BP = 64.7^{\circ}C, \text{ Density} = 0.792\,g/mL$
  • Ethanol: $BP = 78.3^{\circ}C, \text{ Density} = 0.789\,g/mL$
  • 1-Propanol: $BP = 97.2^{\circ}C, \text{ Density} = 0.804\,g/mL$
  • 1-Butanol: $BP = 117.7^{\circ}C, \text{ Density} = 0.810\,g/mL$
  • 1-Pentanol: $BP = 138^{\circ}C, \text{ Density} = 0.817\,g/mL$
  • 1-Hexanol: $BP = 156.5^{\circ}C, \text{ Density} = 0.819\,g/mL$
• Solubility: Lower alcohols are miscible with water in all proportions because they form hydrogen bonds with water. Solubility decreases as the carbon chain length increases.

Preparation and Reactions of Alcohols

• General Preparation:
  • Acid-catalyzed hydration of alkenes: $Alkene + H_2O \xrightarrow{H_3O^+} Alcohol$.
  • Hydrolysis of alkyl halides: $R-X + NaOH \xrightarrow{heat} R-OH + NaX$.
  • Hydrolysis of esters: $RCOOR' + KOH \xrightarrow{heat} RCOOK + R'OH$.
• Industrial Preparation of Ethanol:
  • Fermentation: Decomposition of carbohydrates using enzymes like invertase, diastase, and zymase.
    • $C_{12}H_{22}O_{11} + H_2O \xrightarrow{invertase} C_6H_{12}O_6 + C_6H_{12}O_6$
    • $C_6H_{12}O_6 \xrightarrow{zymase} 2CH_3CH_2OH + 2CO_2$
  • Catalytic Hydration of Ethene: Aqueous ethene at $573\,K$ and $60\,atm$ with $H_3PO_4$ catalyst.
• Chemical Reactions:
  • Reaction with Active Metals: Alcohols react with $Li, Na, K, Mg$ to form metal alkoxides and release hydrogen gas.
    • $2R-OH + 2Na \rightarrow 2R-ONa + H_2$
  • Oxidation:
    • Primary Alcohols: To aldehydes ($R-CHO$) using mild agents ($Cu$ at $360^{\circ}C$) or to carboxylic acids ($R-COOH$) using strong agents ($KMnO_4, K_2Cr_2O_7$).
    • Secondary Alcohols: To ketones ($R-CO-R'$).
    • Tertiary Alcohols: Resistant to oxidation under normal conditions.
  • Dehydration: Removal of water to form alkenes.
    • $CH_3CH_2OH \xrightarrow{Conc. H_2SO_4, 170^{\circ}C} CH_2=CH_2 + H_2O$
  • Reaction with Hydrogen Halides: $R-OH + HX \rightarrow R-X + H_2O$.

Ethers

• Structure: Compounds where an oxygen atom is bonded to two alkyl/aryl groups ($R-O-R'$).
  • Symmetrical: $R = R'$ ($\text{e.g., diethyl ether}$).
  • Unsymmetrical: $R \neq R'$ ($\text{e.g., ethyl methyl ether}$).
• Nomenclature:
  • Common: Name the two alkyl groups alphabetically + "ether."
  • IUPAC: Named as alkoxy substituted alkanes (e.g., methoxyethane).
• Physical Properties:
  • Boiling Points: Much lower than alcohols because they cannot form intermolecular hydrogen bonds with themselves.
  • Solubility: Similar to alcohols of comparable mass due to hydrogen bonding with water molecules. They are excellent solvents for organic reactions because they are relatively inert.
• Preparation:
  • Dehydration of alcohols: $2CH_3CH_2OH \xrightarrow{H_2SO_4, 140^{\circ}C} CH_3CH_2OCH_2CH_3 + H_2O$.
  • Williamson Ether Synthesis: $R-X + R'-O^- \rightarrow R-O-R' + X^-$.
• Chemical Reactions: Ethers do not react with bases or oxidizing agents but can form oxonium salts with proton donors. Cleavage occurs when heated with very strong acids ($HI, HBr$).

Aldehydes and Ketones

• Functional Group: Carbonyl group ($C=O$).
  • Aldehydes: Carbonyl bonded to at least one $H$ ($R-CHO$). Numbering starts at the carbonyl carbon (C-1).
  • Ketones: Carbonyl bonded to two carbons ($R-CO-R'$).
• Nomenclature:
  • Aldehydes: Parent alkane "-e" replaced by "-al."
  • Ketones: Parent alkane "-e" replaced by "-one." For higher ketones, the position must be indicated.
• Physical Properties:
  • Polarity: The $C=O$ bond is polar.
  • Boiling Point: Higher than non-polar compounds (dipole-dipole interactions) but lower than alcohols/acids (no self H-bonding).
  • Solubility: Low molecular weight members are soluble in water (H-bonding with water).

Carboxylic Acids: Classification and Structure

• Definition: Organic compounds containing the carboxyl functional group ($-COOH$ or $-CO_2H$).
• Types:
  • Saturated Monocarboxylic Acids: One carboxyl group attached to $H$ or an alkyl group ($R-COOH$).
  • Dicarboxylic Acids: Contain two carboxyl groups (e.g., Ethanedioic acid/Oxalic acid).
  • Tricarboxylic Acids: Contain three carboxyl groups (e.g., Citric acid).
  • Aromatic Carboxylic Acids: Carboxyl group attached to an aromatic ring (e.g., Benzoic acid).

Nomenclature of Carboxylic Acids

• Common Names: Often derived from Latin/Greek names of natural sources.
  • Formic acid ($HCOOH$): From ants (Formica).
  • Acetic acid ($CH_3COOH$): From vinegar (Acetum).
  • Propionic acid ($CH_3CH_2COOH$): From basic fat (Propio).
  • Butyric acid ($CH_3CH_2CH_2COOH$): From rancid butter (Butyrum).
  • Valeric acid: From valerian herb.
  • Caproic acid: From goats (Caper).
• Substituents in Common Naming: Greek letters ($\alpha, \beta, \gamma$) designate the distance from the carbonyl carbon ($C-2$ is $\alpha$).
• IUPAC Names:
  • Replace alkane "-e" with "-oic acid."
  • Numbering starts at the carboxyl carbon (C-1).
  • Dicarboxylic acids use the suffix "-dioic acid."
  • Aromatic simplest: benzenecarboxylic acid.

Physical Properties of Carboxylic Acids

• State: Lower aliphatic acids ($C_{1-9}$) are liquids; higher members are colourless waxy solids.
• Odor: $-C_1, C_2$ have sharp, irritating odors. $-C_4, C_5, C_6$ have distinctly unpleasant odors.
• Boiling Points: Exceptionally high compared to alcohols/ketones of similar mass due to the formation of stable dimers via double hydrogen bonding.
• Solubility: Carboxylic acids with four or fewer carbons are miscible with water. Solubility decreases with increasing molecular mass.

Chemical Properties of Carboxylic Acids

• Reaction as an Acid: Carboxylic acids partially ionize in water to form carboxylate and hydronium ions.
  • $R-COOH + H_2O \rightleftharpoons R-COO^- + H_3O^+$
• With Active Metals: Forms metal carboxylate salts and hydrogen gas.
  • $2R-COOH + 2Na \rightarrow 2R-COONa + H_2$
• With Bases: Neutralization reactions forming salts and water.
  • Strong Bases: $R-COOH + NaOH \rightarrow R-COONa + H_2O$
  • Weak Bases (Carbonates/Bicarbonates): Reaction yields salt, water, and $CO_2$ gas.
    • $2R-COOH + Na_2CO_3 \rightarrow 2R-COONa + H_2O + CO_2$
• With Ammonia: Forms ammonium salts.
  • $R-COOH + NH_3 \rightarrow R-COONH_4$
• Formation of Esters (Esterification): Carboxylic acids react with alcohols in the presence of concentrated $H_2SO_4$ to form esters.
  • $R-COOH + R'-OH \xrightarrow{H_2SO_4} R-COOR' + H_2O$

Preparation of Carboxylic Acids

• Oxidation of Primary Alcohols: Using $K_2Cr_2O_7$ or $KMnO_4$.
  • $R-CH_2-OH \xrightarrow{KMnO_4} R-COOH$
• Oxidation of Alkylbenzenes: Aromatic compounds with alkyl substituents are oxidized to benzoic acid, irrespective of the alkyl chain length.
  • $Toluene/Ethylbenzene \xrightarrow{KMnO_4, heat} Benzoic\,acid$
• Laboratory Preparation of Acetic Acid: Oxidation of ethanol via distillation with sodium dichromate and sulphuric acid.
• Industrial Preparation of Acetic Acid (Quick Vinegar Process): Ethanol is fermented by bacteria in large wooden vats packed with wood shavings moistened with old vinegar. Recirculation continues until an acetic acid concentration of about $10\%$ is reached. Glacial acetic acid is the anhydrous form.

Fatty Acids

• Definition: Long-chain monocarboxylic acids (usually unbranched with an even number of carbon atoms).
• Saturated vs. Unsaturated:
  • Saturated: No double bonds. Melting point increases with molecular weight.
    • Lauric acid ($C_{12}, MP = 44^{\circ}C$), Palmitic acid ($C_{16}, MP = 63^{\circ}C$), Stearic acid ($C_{18}, MP = 69^{\circ}C$).
  • Unsaturated: Contain one or more double bonds (non-conjugated). Double bonds lower the melting point significantly.
    • Palmitoleic acid ($C_{16}, MP = 0^{\circ}C$), Oleic acid ($C_{18}, 1\,db, MP = 13^{\circ}C$), Linoleic acid ($C_{18}, 2\,db, MP = -5^{\circ}C$), Linolenic acid ($C_{18}, 3\,db, MP = -11^{\circ}C$).

Esters: Properties and Preparation

• General Formula: $R-COOR'$ or $RCO_2R'$.
• Sources: Found in fruits and flowers, providing flavors and fragrances. Examples:
  • Apple: Isoamyl isovalerate.
  • Banana: Isopentyl acetate.
  • Orange: Octyl acetate.
  • Pineapple: Ethyl butyrate.
• Nomenclature: The first part is from the alcohol (-yl) and the second part is from the acid (-ate or -oate).
• Physical Properties:
  • Lower boiling points than parent acids/alcohols (no self H-bonding).
  • Low molecular mass esters are water-soluble (H-bonding with water).
  • Generally pleasant odors.
• Chemical Properties:
  • Hydrolysis: Yields acid and alcohol. Catalyzed by acid or base.
    • Saponification: Base-catalyzed hydrolysis (irreversible).
      • $CH_3COOCH_2CH_3 + NaOH \rightarrow CH_3COONa + CH_3CH_2OH$
  • Reduction: Reduced to primary alcohols using $LiAlH_4$.
    • $R-COOR' \xrightarrow{1.\,LiAlH_4, 2.\,H^+} R-CH_2OH + R'-OH$
• Uses: Perfumes, food flavorings, solvents for paints/varnishes, medicines (Aspirin), and plastics.

Fats and Oils

• Definition: Triesters of glycerol known as triglycerides or triacylglycerols.
• Structure: Fatty acid chains ($R_1, R_2, R_3$) attached to a glycerol backbone.
• Difference:
  • Fats: Saturated fatty acids; solid/semi-solid at room temperature; animal origin.
  • Oils: Unsaturated fatty acids; liquid at room temperature; plant origin.
• Physical Properties: Greasy, lubricating, non-volatile, lighter than water, insoluble in water but soluble in organic solvents ($\text{benzene, ether, chloroform}$).
• Hardening of Oils: The process of converting liquid oils to solid fats through hydrogenation using a nickel or palladium catalyst at high pressure.
  • $Glyceryl\,trioleate + 3H_2 \xrightarrow{Ni} Glyceryl\,tristearate$
• Rancidity: Spoilage of fats/oils characterized by unpleasant odors caused by hydrolysis of ester linkages and oxidation across double bonds. Development is accelerated by high temperatures and air exposure.

Questions & Discussion

• Exercise 6.11: Write reactions of ethanoic acid with $KOH, Na_2CO_3, NH_3$; name the products.
• Question on Melting Points: Why do unsaturated fatty acids have lower melting points than saturated ones of similar weight?
  • Answer: Unsaturation (double bonds) introduces kinks in the chain, preventing molecules from packing closely together, thereby weakening van der Waals forces.
• Omega Fatty Acids: Discussion prompted on the difference between omega-3 and omega-6 fatty acids and essential fatty acids.
• Activity 6.17: Observation of rancidity in potato chips stored in different conditions (open vs. closed containers) over 15 days.
• Health/Dietary Sources: Saturated fats (Beef, Dairy, Lard, Coconut oil); Unsaturated fats (Avocados, Nuts, Canola, Fatty fish).