Organic Chemistry Level 2 – Comprehensive Study Notes

Functional Groups – Identification & Priority Order

  • A functional group is the portion of an organic molecule that determines its characteristic chemical behaviour.
  • Groups required for AS 2.5 (ordered by IUPAC priority for secondary suffix)
    • Carboxylic acid: ‑COOH ⇒ name ends in “oic acid”
      • Example: butanoic acid
    • Alcohol (hydroxyl): ‑OH ⇒ “-#-ol” ; as prefix “hydroxy-”
      • Example: butan-1-ol; 2\text{-hydroxy}ethanoic\,acid
    • Amine (primary): ‑NH₂ ⇒ “-#-amine” ; as prefix “amino-”
    • Alkyne: C≡C ⇒ “-#-yne”
    • Alkene: C=C ⇒ “-#-ene”
    • Alkane: C–C only ⇒ “-e”
    • Haloalkane: F, Cl, Br, I substituents ⇒ prefix fluoro-, chloro-, bromo-, iodo-
  • Classification of alcohols & haloalkanes
    • Primary: C bearing OH / X attached to ONE other carbon
    • Secondary: attached to TWO carbons
    • Tertiary: attached to THREE carbons
    • Required wording for explanations: “The \text{OH} (or \text{Cl/Br/etc.}) group is bonded to a C which is directly attached to ___ other C atoms.”

IUPAC Naming Strategy (up to 8 carbons)

  1. Identify ALL functional groups present.
  2. Select the longest chain containing the highest-priority group and all multiple bonds.
  3. Number the chain from the end nearest the highest-priority group.
  4. Primary suffix – degree of saturation
    • all single bonds: “-an-”
    • one C=C: “-#-en-”
    • two C=C: “-#,#-dien-”
    • one C≡C: “-#-yn-” etc.
  5. Secondary suffix – highest-priority functional group (see list above).
  6. Prefixes – side chains & low-priority groups (methyl, chloro, hydroxy …). Separate numbers with commas, numbers/letters with hyphens.
  7. Assemble name: prefix(es) + root + infix (cyclo) + primary suffix + secondary suffix.
  • Example full name
    • 3\text{-amino-2-fluoro-5-hydroxy-pent-2-en-4-ynoic\,acid}

Drawing Structures from a Name

  1. Pencil-number the C’s of the parent chain.
  2. Sketch the parent C-C skeleton (include double/triple bonds).
  3. Add functional groups/branches at indicated positions.
  4. Check every carbon has 4 bonds; add hydrogens accordingly.

Types of Formulae

  • Expanded/Displayed: every atom & bond shown.
  • Condensed: written in one line, e.g. \text{CH}_3\text{CH(OH)COOH}

Structural (Constitutional) Isomerism

  • Same molecular formula, different connectivity.
    • Chain/Branch isomers – vary backbone.
    • Positional – same group, different position.
    • Functional group isomers – different groups altogether.
  • Answer framework (A/M/E): state same molecular formula + different arrangement; link to specific structures.

Geometric (cis-trans) Isomerism

Requirements

  1. Rigid double bond (C=C) – no rotation.
  2. Each C of the double bond has two different substituents.
    Decision tree
  • If requirement 2 fails → no geometric isomers.
  • If satisfied, compare like groups:
    • Same side → cis
    • Opposite sides → trans
      Model explanation must reference rigidity of C=C and identity of attached groups.

Reaction Types – Overview

  • Substitution: one group replaces another on same carbon.
  • Addition: reagent adds across C=C (or C≡C), breaking the π bond.
  • Elimination: small molecule removed to form C=C.
  • Oxidation: carbon gains O (or loses H/e⁻).
  • Acid–Base: proton transfer between acid donor and base acceptor.
  • Addition polymerisation: many unsaturated monomers join to make a saturated chain.

Substitution Reactions – Details & Equations

  1. Alkane + \text{Br}2/\text{Cl}2 + UV → haloalkane + HBr/HCl (slow, free-radical)
    \text{CH}3\text{CH}3 + Br2 \xrightarrow{h\nu} \text{CH}3\text{CH}_2Br + HBr
  2. Haloalkane + \text{KOH(aq)} (reflux) → alcohol (nucleophilic)
  3. Haloalkane + \text{NH}_3(alc) (reflux) → amine + HX
  4. Alcohol + \text{SOCl}2 / \text{PCl}3 / \text{PCl}5 (heat) → chloroalkane (+ inorganic products SO2,HCl etc.)
    Explanation point: an incoming nucleophile (OH⁻, NH₃) replaces leaving group (Br⁻, Cl⁻).

Addition Reactions of Alkenes

Reagent | Conditions | Product(s)

  • H_2 | Ni, high T/P | alkane (hydrogenation)
  • Br2/Cl2 (room T) | | dihaloalkane (halogenation)
  • H2O/H^+ (dil. H2SO_4, reflux) | | alcohol (hydration)
  • HX (HCl, HBr) | RT | haloalkane
  • Polymerisation: initiator, heat/pressure → poly(alkene)
    Markovnikov Rule (asymmetric alkene + asymmetric reagent):
  • “H adds to the C already bearing more H”; gives major vs minor products.
    Example: but-1-ene + HBr → major 2\text{-bromobutane}, minor 1\text{-bromobutane}.

Addition Polymerisation

  • Definition: joining of many monomers to form a large molecule (polymer) with loss of π bonds.
  • Monomer requirement: C=C or C≡C.
  • Mechanism (simplified):
    1. Align monomers.
    2. Break π bond; form new σ bonds between C’s to give repeating unit.
    3. Represent polymer with brackets and subscript n.
  • Example polypropene:
    n\,(CH3CH=CH2) \rightarrow [-CH2-CH(CH3)-]_n
  • Reactivity: monomer is more reactive because of the unsaturated bond; polymer is saturated (C–C/C–H only).
  • Geometric isomer monomers give identical polymer because double bond is destroyed.

Elimination Reactions & Saytzeff’s Rule

  1. Alcohol → alkene + H2O (conc. H2SO_4, reflux) – dehydration.
  2. Haloalkane → alkene + HX (KOH(alc), reflux).
    Saytzeff (Zaitsev) orientation
  • For asymmetric substrate, the H removed comes preferentially from the β-carbon with FEWER hydrogens → more substituted (major) alkene.
    Example: 2-chlorobutane + KOH(alc) → major \text{CH}3CH=CHCH3 (but-2-ene) vs minor but-1-ene.

Oxidation Reactions & Observations

  • Reagents
    • \text{MnO}4^- (permanganate): • Neutral or acidified. Colour change: purple → colourless (acid) or purple → black/brown MnO2 (neutral).
    • \text{Cr}2O7^{2-}/H^+ (dichromate): orange → green.
  • Specific reactions
    1. Alkene + KMnO_4 → diol (break π bond, add OH to each C).
    2. Primary alcohol + Cr2O7^{2-}/H^+ (heat) → carboxylic acid.
      Explanation wording: “oxidation = carbon gains an O atom”.

Acid–Base Reactions (Weak Acid/Base Behaviour)

  • Carboxylic acids donate H^+ to form carboxylate RCOO^-.
    • With H2O ⇌ RCOO^- + H3O^+ (weak acid)
    • With Na2CO3 / NaHCO3 → RCOO^- Na^+ + CO2 + H_2O (bubbling test)
    • With base NaOH → salt + H_2O
    • With amine R'NH2 → RCOO^- + R'NH3^+ (organic salt)
  • Amines accept H^+ ⇒ ammonium salts.
    • With H2O ⇌ RNH3^+ + OH^- (basic litmus test)
    • With HCl → RNH_3^+Cl^-

Chemical Tests – Summary Table

Reagent | Positive group(s) | Observation | Reaction type | Organic product

  • Cr2O7^{2-}/H^+ (heat) | 1°/2° alcohol | orange → green | oxidation | carboxylic acid
  • MnO_4^- /H^+ | alkene, 1°/2° alcohol | purple → colourless | oxidation | diol / acid
  • Neutral MnO_4^- | alkene | purple → black ppt | oxidation | diol
  • Br_2 (aq) | alkene | orange → colourless (fast) | addition | dibromoalkane
  • Br_2 + UV | alkane | slow decolourisation | substitution | bromoalkane
  • Moist litmus
    • Blue → red: carboxylic acid
    • Red → blue: amine
  • Na2CO3/NaHCO3 | carboxylic acid | effervescence CO2 | acid–base | carboxylate salt
  • Solubility tests
    • In H_2O: alcohols/amines/acids soluble; alkanes etc. insoluble (2 layers).
    • In hexane (non-polar): opposite behaviour.

Comparing Reaction Pairs

  • Haloalkane + KOH(aq) (reflux) → alcohol (substitution) vs alcohol + KOH(alc) → alkene (elimination).
  • Alkene + dil. H2SO4/H2O → alcohol (addition) vs alcohol + conc. H2SO4 → alkene + H2O (elimination).
  • Alkane vs alkene with Br_2(aq): both decolourise, but alkane needs UV and is slower (substitution) whereas alkene is fast (addition) and gives single product (dibromoalkane).

Reaction Scheme Shorthand (common reagents)

Letter | Reagent & conditions | Reaction type
A | H2, Ni, high T/P | Addition (hydrogenation) B | Br2, UV | Substitution
C | NH3(alc), reflux | Substitution to amine D | HCl(aq) (with acid) | Acid–base E | HCl/HBr (to alkene) | Addition F | KOH(alc), reflux | Elimination G | Initiator (radical) | Addition polymerisation H | Br2 (no UV) | Addition to alkene
I | MnO4^-/H^+ or neutral MnO4^- | Oxidation
J | H2O/H^+ , dil\,H2SO4 | Addition (hydration) K | conc. H2SO4, reflux | Elimination (dehydration) M | SOCl2/PCl3/PCl5 | Substitution
N | Cr2O7^{2-}/H^+ or MnO4^-/H^+ | Oxidation O | Na2CO3, NaOH, NH3(aq) | Acid–base

Major/Minor Product Rules

  • Addition (Markovnikov): H adds to C with more H.
  • Elimination (Saytzeff): H is removed from β-C with fewer H → more substituted alkene major.

Physical-Property Summary

Functional group | In water | In hexane | Reason
Polar (alcohol, amine, acid) | Single colourless layer (soluble) | Two layers (insoluble) | Can H-bond with H_2O, but not with non-polar solvent.
Non-polar (alkane, alkene, alkyne, haloalkane) | Two layers | Single layer | London forces only, miscible with non-polar solvent.

Learning / Exam Targets (Condensed)

Achieved (A):

  • Identify & name functional groups; draw basic structures; state reaction type; give test observations.
    Merit (M):
  • Explain reaction mechanisms (one reaction); explain isomer requirements; distinguish compounds with tests; 70 % of reaction-scheme blanks.
    Excellence (E):
  • Justify presence/absence of isomerism; compare/contrast reactions under different conditions; give full reaction schemes & equations; link observations to functional-group changes.
  • Polymer formation vs environmental persistence: saturated C–C polymer backbone makes plastics chemically inert → disposal issues.
  • UV-initiated halogenation parallels atmospheric free-radical chemistry (e.g. ozone depletion by Cl\cdot).
  • Acid–base behaviour of amino & carboxyl groups underpin biochemistry of amino acids/proteins.