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 + $\text{Br}<em>2/\text{Cl}</em>2$ + UV → haloalkane + HBr/HCl (slow, free-radical)
   $\text{CH}<em>3\text{CH}</em>3 + Br<em>2 \xrightarrow{h\nu} \text{CH}</em>3\text{CH}_2Br + HBr$
2. Haloalkane + $\text{KOH(aq)}$ (reflux) → alcohol (nucleophilic)
3. Haloalkane + $\text{NH}_3(alc)$ (reflux) → amine + HX
4. Alcohol + $\text{SOCl}<em>2$ / $\text{PCl}</em>3$ / $\text{PCl}<em>5$ (heat) → chloroalkane (+ inorganic products $SO</em>2,HCl$ 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)
• $Br<em>2/Cl</em>2$ (room T) | | dihaloalkane (halogenation)
• $H<em>2O/H^+$ (dil. $H</em>2SO_4$, 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:
  $n\,(CH<em>3CH=CH</em>2) \rightarrow [-CH<em>2-CH(CH</em>3)-]_n$
• 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 + $H<em>2O$ (conc. $H</em>2SO_4$, 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 $\text{CH}<em>3CH=CHCH</em>3$ (but-2-ene) vs minor but-1-ene.

Oxidation Reactions & Observations

• Reagents
  • $\text{MnO}<em>4^-$ (permanganate): • Neutral or acidified. Colour change: purple → colourless (acid) or purple → black/brown $MnO</em>2$ (neutral).
  • $\text{Cr}<em>2O</em>7^{2-}/H^+$ (dichromate): orange → green.
• Specific reactions
  1. Alkene + $KMnO_4$ → diol (break π bond, add $OH$ to each C).
  2. Primary alcohol + $Cr<em>2O</em>7^{2-}/H^+$ (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 $H<em>2O$ ⇌ $RCOO^- + H</em>3O^+$ (weak acid)
  • With $Na<em>2CO</em>3 / NaHCO<em>3$ → $RCOO^- Na^+ + CO</em>2 + H_2O$ (bubbling test)
  • With base $NaOH$ → salt + $H_2O$
  • With amine $R'NH<em>2$ → $RCOO^- + R'NH</em>3^+$ (organic salt)
• Amines accept $H^+$ ⇒ ammonium salts.
  • With $H<em>2O$ ⇌ $RNH</em>3^+ + OH^-$ (basic litmus test)
  • With $HCl$ → $RNH_3^+Cl^-$

Chemical Tests – Summary Table

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

• $Cr<em>2O</em>7^{2-}/H^+$ (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
• $Na<em>2CO</em>3/NaHCO<em>3$ | carboxylic acid | effervescence $CO</em>2$ | 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. $H<em>2SO</em>4/H<em>2O$ → alcohol (addition) vs alcohol + conc. $H</em>2SO<em>4$ → alkene + $H</em>2O$ (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 | $H<em>2$, Ni, high T/P | Addition (hydrogenation) B | $Br</em>2$, UV | Substitution
C | $NH<em>3(alc)$, 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 | $Br</em>2$ (no UV) | Addition to alkene
I | $MnO<em>4^-/H^+$ or neutral $MnO</em>4^-$ | Oxidation
J | $H<em>2O/H^+$ , $dil\,H</em>2SO<em>4$ | Addition (hydration) K | conc. $H</em>2SO<em>4$, reflux | Elimination (dehydration) M | $SOCl</em>2/PCl<em>3/PCl</em>5$ | Substitution
N | $Cr<em>2O</em>7^{2-}/H^+$ or $MnO<em>4^-/H^+$ | Oxidation O | $Na</em>2CO<em>3$, $NaOH$, $NH</em>3(aq)$ | 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.

Ethical & Real-World Links

• 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.