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)

Longest chain containing $-OH$
Number chain giving hydroxyl lowest number
Name & locate every substituent
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: $CH3CH2OCH2CH3$