Alcohols, Phenols, Thiols & Ethers: Functional Groups, Naming, Properties & Health Connections

Functional Group Fundamentals

• Core organic functional groups in this chapter
  • Alcohol → hydroxyl group ( -OH ) bonded to an sp$^3$ carbon
  • Phenol → hydroxyl group attached directly to a benzene ring
  • Thiol → sulfhydryl/thiol group ( -SH ) bonded to carbon
  • Ether → oxygen bridging two carbon fragments ( C-O-C )
• Structural analogy
  • Alcohols/phenols & water share a bent geometry around O; ethers have a similar ~104° bond angle
• Practical context: Dermatology nurses and many medical practitioners routinely handle compounds with these functional groups (e.g.
  antiseptics, anesthetics, prescription creams)

Recognising Functional Groups: Visual & Formula Examples

• Methanol: Ball-and-stick shows single C with -OH; condensed CH_3OH; line-angle terminates in “–OH”
• Phenol: Aromatic hexagon plus -OH
• Ethanethiol: CH3CH2SH (distinct garlic-like odour)
• Dimethyl ether: CH3OCH3, first-row ether example
  • Note: lone pairs on O not shown in condensed formula but control physical properties

Systematic & Common Naming Rules

Alcohols

• IUPAC: replace “-e” of parent alkane with “-ol” ; number chain to give C bearing -OH lowest possible locant
• Common: name alkyl group + “alcohol” (e.g. “methyl alcohol”)
• Multiple -OH groups → use suffixes “-diol”, “-triol” etc. with full numeric locants

Phenols

• Base name = phenol; substituents numbered with OH at C-1

Thiols

• Add suffix “-thiol” to longest alkane; number from end nearer -SH

Ethers (common names predominantly used)

• Alphabetise the two alkyl / aryl substituents + word “ether” (e.g. diethyl ether, methyl tert-butyl ether)

Step-Wise IUPAC Naming Strategy (Illustrated)

1. Longest chain containing -OH
2. Number chain giving hydroxyl lowest number
3. Name & locate every substituent
4. Replace terminal “-e” with “-ol”; insert commas & hyphens per IUPAC conventions

• Example walk-through (6-carbon skeleton with CH$_3$ substituent and OH)
  1. Parent = hexanol
  2. Number to put OH at C-2
  3. Methyl at C-4 → Final: 4-methyl-2-hexanol
• Learning Check practice
  • 5-carbon example with OH at C-2 & CH$_3$ at C-4 → 4-methyl-2-pentanol
  • Bromophenol example → 4-bromophenol (OH locant implicit =1)

Structural Drawing Skills

• Condensed, expanded, and line-angle interconvertible; exam often asks both directions
• Practice structures from prompts
  • 3-Pentanol: CH3CH2CH(OH)CH2CH3
  • Ethanol: CH3CH2OH
  • Diethyl ether: CH3CH2OCH2CH3 (symmetrical)

Classification of Alcohols (1°, 2°, 3°)

• Based on number of carbon substituents attached to carbon bearing the hydroxyl
  • Primary (1°): RCH_2OH
  • Secondary (2°): R_2CHOH
  • Tertiary (3°): R_3COH
• Importance: governs oxidation pathways & metabolic toxicity
• Example set
  • 2-propanol → 2°
  • 1-butanol → 1°
  • tert-butyl alcohol (2-methyl-2-propanol) → 3°

Physical Properties & Solubility Trends

Alcohols

• Hydrogen-bond donors & acceptors ⇒ elevated b.p. relative to alkanes/ethers of similar mass
• Water solubility:
  • 1–3 C: miscible (methanol, ethanol, 1-propanol)
  • 4 C: slightly soluble
  • ≥5 C: essentially insoluble (hydrophobic tail dominates)
• Table 12.1 snapshot (number of carbons vs qualitative solubility)

Phenols

• Slightly soluble; acidic proton forms phenoxide PhO^- in basic solution
• Historical antiseptic (Joseph Lister)

Ethers

• Lack O–H; only H-bond acceptor ⇒ lower b.p. than isomeric alcohol
• Moderately polar, good solvents; limited water solubility (cannot donate H-bond)

Thiols: Properties & Applications

• Sulfur analog of alcohol; less electronegative & larger → weaker H-bonding, lower b.p.
• Often pungent/skunk-like odours; occurring in cheese, garlic, onions
• Added (in ppb) to natural gas as leak-detection odorants
• Oxidation leads to disulfides R-S-S-R important in protein tertiary structure (cystine)

Health & Industrial Linkages

Ethanol

• Produced by fermentation or hydration of ethene at high T/P
• Uses: beverages, solvent (perfumes, tincture of iodine), sanitizer (60–85% v/v)

1,2,3-Propanetriol (Glycerol)

• By-product of soap; triol with three -OH groups ⇒ highly hygroscopic, skin emollient

Ethylene Glycol (1,2-ethanediol)

• Antifreeze; also solvent & polyester precursor (Dacron). Sweet taste risks poisoning; metabolism to oxalic acid yields renal-damaging Ca-oxalate

Bisphenol A (BPA)

• Monomer of polycarbonate plastics; leaches upon harsh washing; endocrine disruptor controversy

Phenolic Essential Oils

• Plant secondary metabolites; responsible for aromatic flavours (clove, thyme, oregano)

Ethers as Inhalation Anesthetics

• Diethyl ether historic anesthetic; volatility/flammability problematic
• Modern agents (e.g. halothane, isoflurane) retain C-O-C core but incorporate halogens → less flammable, more potent

Hand Sanitizers

• Ethanol/propanol base kills microbes; transparent blue flame hazard
• Additive triclosan may foster antibiotic resistance & persists environmentally

Safety, Ethical & Practical Implications

• Flammability of alcohols mandates proper storage (health-care settings, home sanitizers)
• BPA leaching raises public health/infant safety debates
• Ethylene glycol poisoning in pets/children ⇒ legislation on bittering agents
• Sterilisation vs resistance dilemma with triclosan usage

Practice & Self-Check Summary

• Be able to:
  • Identify functional groups in skeletal structures
  • Assign correct IUPAC names including locants & multiple -OH
  • Classify alcohols (1°,2°,3°) and predict oxidation outcomes
  • Predict relative boiling points & water solubilities from structural features
  • Draw condensed/line-angle formulas for specified names
• Typical exam prompt: “Draw and name all structural/positional isomers of C4H{10}O; classify each as alcohol or ether and predict solubility.”

Quick Formula Reference

• Methanol: CH_3OH
• Ethanol: CH3CH2OH
• 2-Propanol: (CH3)2CHOH
• Glycerol: HOCH2CH(OH)CH2OH
• Ethylene glycol: HOCH2CH2OH
• Ethanethiol: CH3CH2SH
• Dimethyl ether: CH3OCH3
• Diethyl ether: CH3CH2OCH2CH3