A2 Organic Chemistry Notes by Fahad Hameed

Typed version of Fahad Hameed's handwritten A2 Organic Chemistry notes for Cambridge International A Level Chemistry (9701). Every page of the original is typed in the same order, with drawn structures named and written as formulae, and drawn mechanisms written as numbered steps, so the notes can be searched and copied. The handwritten original is on the same page of megalecture.com.

Introduction to Organic Chemistry

Organic: chemistry of carbon compounds.

• biological molecules
• fossil fuels

Formulas

Molecular formula: C₂H₄O₂. Total number of atoms of elements in a molecule (no information about structure).

Structural formula

1. Fully displayed formula

All atoms and bonds shown.

• C: 4 bonds
• N: 3 bonds
• O: 2 bonds
• H: 1 bond
• Halogen: 1 bond

N and O: lone pairs can form dative bonds.

Displayed formulas drawn with every atom and bond shown:

• butanone, CH₃COCH₂CH₃
• HOOCCH₂COOCH₃ (a carboxylic acid group at one end and a methyl ester group at the other)

2. Condensed structural formula

The displayed formula H–O–C(=O)–CH₂–C(=O)–O–CH₃ is written as HOOCCH₂COOCH₃.

The displayed formula of 2-hydroxy-2,3-dimethylbutanoic acid, counted along the main chain with the branches (CH₃, OH and CH₃) circled, is written as CH₃CH(CH₃)C(OH)(CH₃)COOH.

Aldehydes: R–C(=O)–H is written as R–CHO.

3. Skeletal formula

C–C bonds shown only, and any functional group.

The same molecule, 2-hydroxy-2,3-dimethylbutanoic acid, CH₃CH(CH₃)C(OH)(CH₃)COOH, is drawn again as a displayed formula with each carbon marked by a dot, and then as a skeletal formula: a zigzag carbon chain with a line for each methyl branch, an OH on carbon 2 and the C(=O)OH group at the end.

Naming (simple naming)

Prefix	Number of carbons
meth	1C
eth	2C
prop	3C
but	4C
pent	5C
hex	6C
hept	7C
oct	8C
non	9C
dec	10C

Then: an or en.

Family	Suffix
alkane	-ane
alkene	-ene (position of C=C)
alcohol	-ol (position of OH)
carboxylic acid	-oic acid
nitriles	-nitrile
aldehyde	-al
ketones	-one (position of C=O)

CH₃CH=CHCOOH, numbered 4, 3, 2, 1 starting from the COOH carbon: but-2-enoic acid (but / 2-en / oic acid).

CH₃COCH₂CH₃, with the C=O carbon as carbon 2: butan-2-one.

Counting is done from the side which gives the smaller number to the higher precedence group (the suffix).

RCOOH > nitriles > aldehyde > ketones > alcohols (hydroxy branch) > amines (amino branches) > C=C

OHC–CH(OH)–CH₂–COOH, numbered 4, 3, 2, 1 starting from the COOH carbon. The groups are labelled aldehyde (carbon 4), alcohol (hydroxy, carbon 3) and carboxylic acid (carbon 1).

3-hydroxybutan-4-aloic acid

CH₃–CH(NH₂)–CH₂–OH, numbered 3, 2, 1 starting from the carbon with OH. The groups are labelled amine and alcohol.

2-aminopropan-1-ol

Branches

Order of the name: position, branch (alphabetical), longest carbon atom chain.

Choosing the longest carbon atom chain:

• more substituent groups
• maximum C=C
• highest precedence group (ticked)

Example: CH₃CH(CHO)CH=C(CH₃)CH(OH)CH₃. The main chain is highlighted and numbered from the aldehyde carbon: carbon 1 is CHO, carbon 2 is CH, carbon 3 is CH=, carbon 4 is =C, carbon 5 is CH(OH), carbon 6 is CH₃. Circled branches: methyl on carbon 2, methyl on carbon 4, hydroxy on carbon 5.

5-hydroxy-2,4-dimethylhex-3-enal

The same molecule is drawn as a skeletal formula: a six-carbon zigzag chain with the C=O and H of the aldehyde at carbon 1, a methyl branch on carbon 2, the double bond between carbons 3 and 4, a methyl branch on carbon 4 and HO on carbon 5.

Isomers

Structural isomers

Same molecular formula, different structural formula (different arrangement of atoms).

(a) Chain / branch isomers

C₅H₁₂:

• pentane, CH₃CH₂CH₂CH₂CH₃
• 2-methylbutane, CH₃CH₂CH(CH₃)CH₃
• 2,2-dimethylpropane, C(CH₃)₄

(b) Positional isomer

Change position of a functional group.

• CH₃CH₂CH=CH₂, but-1-ene
• CH₃CH=CHCH₃, but-2-ene

(c) Functional group isomer

CH3CH2CHO, propanal	CH3COCH3, propanone
CH3CH2COOH, carboxylic acid	CH3COOCH3, ester
CH3CH=CH2, alkene	cyclopropane, a ring of three CH2 groups (C3H6), cycloalkane

Stereoisomers

Same molecular formula, same structural formula but different 3-dimensional geometry.

(a) Geometric isomers

• C=C present
• each C must be bonded to two different groups

1,2-dichloroethene, CHCl=CHCl, drawn with the pi bond shaded above and below the C=C:

• cis: both Cl atoms on the same side of the C=C (both H on the other side)
• trans: the two Cl atoms on opposite sides of the C=C

Rotation is restricted around a C=C / pi bond.

(CH₃)₂C=CH–CH=CHCl: the first C=C is marked with a cross, because one of its carbons carries two CH₃ groups (circled). The second C=C is marked with a tick, cis / trans, because each carbon carries two different groups (H and Cl circled).

• cis: (CH₃)₂C=CH– and Cl on the same side of the C=C, the two H atoms on the other side
• trans: (CH₃)₂C=CH– and Cl on opposite sides of the C=C

Unsymmetric molecule

n × (C=C) with cis / trans → 2ⁿ different geometric isomers.

e.g. Cl–CH=CH–CH=CH–CH₃: each C=C is cis / trans, so 2² = 4.

First C=C	Second C=C
cis	cis
trans	trans
cis	trans
trans	cis

Optical isomers

(Enantiomers. A mixture of enantiomers → racemate / racemic mixture.)

Chiral carbon: sp³ hybridised / tetrahedral, 109.5°. C makes 4 single bonds with 4 different groups.

→ two non-superimposable mirror images.

Butan-2-ol, CH₃CH(OH)CH₂CH₃, drawn as two tetrahedral structures on either side of a mirror line. The chiral carbon (C*) carries H, CH₃, CH₂CH₃ (dashed bond) and OH (wedge bond). One is labelled (+) and its mirror image (−).

Both enantiomers rotate plane polarised monochromatic light in opposite directions (clockwise / anticlockwise).

Printed figure: a light source, a polariser and a sample tube, shown twice. Optically active compounds rotate the plane of the polarised light. Optically inactive compounds do not rotate the plane of the polarised light.

Skeletal drawing: two fused six-membered carbon rings with a Cl on one ring, two CH₃ branches on the other ring, and a side carbon carrying OH and CH₃. The chiral carbons are circled on the original drawing.

Small enantiomers usually have exactly the same chemical and physical properties.

• Large biologically / shape specific molecules will have drastically different functions if stereochemistry is changed.

Alkanes

Saturated hydrocarbons, C_nH_2n+2.

Displayed formula of 2-methylbutane, CH₃CH₂CH(CH₃)CH₃.

sp³ hybridisation: all single bonds, no π bond / double bond.

2s¹, 2p_x¹, 2p_y¹, 2p_z¹ (each crossed out) become sp³, sp³, sp³, sp³, with one electron in each.

Hybridisation: mixing of orbitals to form new hybrid orbitals during bond formation.

Diagram: a carbon atom with four sp³ orbitals, each holding one electron, each pointing towards an H atom.

Free radical substitution

Cl₂ or Br₂ + UV light.

• Substitute Cl or Br into any alkyl chain.

CH₃CH₂COCOOH + Cl₂ → CH₃CHClCOCOOH + HCl (Cl₂ + UV light). HCl is the by-product.

Another product drawn: CHCl₂CHClCOCOOH.

The number / position of H atoms being substituted is random / multiple products produced.

Mechanism

1. Initiation: free radicals are produced.

1. Cl–Cl → Cl• + Cl• (UV light). The Cl–Cl bond breaks and one electron of the bonding pair goes to each Cl atom (one curly arrow from the bond to each Cl).

Free radical: species with an unpaired electron, very reactive.

2. Propagation: radicals attack H atoms.

1. CH₃CH₂CH₃ + Cl• → CH₃CH₂CH₂• + HCl. A C–H bond on the end carbon breaks. One electron of that bond stays on the carbon, the other pairs with the unpaired electron of Cl• to form H–Cl. A propyl radical is formed.
2. CH₃CH₂CH₂• + Cl₂ → CH₃CH₂CH₂Cl + Cl•. The unpaired electron on the carbon pairs with one electron of the Cl–Cl bond to form a C–Cl bond. The other electron of the Cl–Cl bond goes to the second Cl, so Cl• is regenerated.
3. ClCH₂CH₂CH₃ + Cl• → ClCH₂CH₂CH₂• + HCl. A C–H bond on the carbon at the other end from the Cl breaks. One electron stays on the carbon, the other pairs with the unpaired electron of Cl• to form H–Cl.
4. ClCH₂CH₂CH₂• + Cl₂ → ClCH₂CH₂CH₂Cl + Cl•. The unpaired electron on the carbon pairs with one electron of the Cl–Cl bond to form a C–Cl bond, and Cl• is regenerated.

3. Termination: free radicals combine randomly.

1. CH₃CH₂CH₂• + •CH₂CH₂CH₃ → CH₃CH₂CH₂CH₂CH₂CH₃ (hexane). The unpaired electrons on the two end carbons pair up to form a new C–C bond, giving a six-carbon chain.
2. CH₃CH₂CH₂• + •Cl → CH₃CH₂CH₂Cl. The unpaired electron on the carbon pairs with the unpaired electron of Cl• to form a C–Cl bond.

Crude oil

Source of most hydrocarbons.

Printed figure: Fractional Distillation of Crude Oil. Crude oil is heated until it evaporates. The vapour rises up the column and the fractions condense at different levels: the larger hydrocarbons with high boiling points turn back into liquids at the base, and the smaller hydrocarbons rise further up the column. Some hydrocarbons with low boiling points (between 20 °C and 70 °C) remain as gases at the top.

Fraction	Temperature	Use
Refinery gas	20 °C	Bottled gas
Petrol	70 °C	Petrol for vehicles
Naphtha	120 °C	Chemicals
Kerosene	170 °C	Jet fuel, paraffin for lighting and heating
Diesel	270 °C	Diesel fuels
Lubricating oil	Lubricating oils, waxes and polishes
Fuel oil	Fuel for ships, factories and central heating
Bitumen	340 °C	Roads and roofing

Small molecules (top of the column)	Large molecules (bottom of the column)
Low boiling point	High boiling point
Light in colour	Dark in colour
Easy to light	Hard to light
Runny	Thick

Cracking

Zeolites / pumice. Al₂O₃ + temperature > 450 °C.

From	Reagents and conditions	To
Long chain hydrocarbon	Zeolites / pumice, Al2O3, temperature > 450 °C	Smaller chain: alkanes, alkene, hydrogen

Long chain hydrocarbon	Smaller chain products
not very useful	more flammable
big molecules / more van der Waals	less viscous
high melting point / boiling point / viscosity	low melting point / boiling point
low flammability	lesser van der Waals

Structure of Benzene and Alkene

Alkenes

"C=C"

Carbon is sp² hybridised.

2s¹, 2p_x¹, 2p_y¹ (struck through) become sp², sp², sp². 2p_z¹ is circled and left as it is.

Diagram: one carbon atom with three sp² orbitals, each holding one electron, arranged trigonal planar at 120°, and the p orbital above and below the plane.

Ethene, CH₂=CH₂, drawn with each carbon labelled sp².

Orbital diagram of ethene:

• sp²–sp² overlap between the two carbon atoms, holding two electrons
• sp²–s overlap between each carbon and its two H atoms (four in total)
• p–p overlap above and below the plane, forming the π bond

The π bond has high electron charge density. It attracts electrophiles VERY STRONGLY.

Benzene

Simplified version / Kekulé structure (don't use this). (1 : 1 ratio is only possible in benzene.)

C₆H₆: a ring of six carbon atoms, each bonded to one H, drawn with alternating single and double bonds between the carbons.

sp² hybridised (all carbon atoms in benzene).

Benzene, C₆H₆, drawn as an orbital diagram: six carbon atoms in a ring, each bonded to one hydrogen, with a p orbital above and below every carbon overlapping sideways all round the ring. Beside it, benzene drawn as a hexagon of six C atoms, each with one H, and a circle inside the ring.

Hexagonal planar, 120°.

• C–C σ bonds: sp²–sp² overlap.
• C–H σ bonds: sp²–s overlap.
• π bonds: p–p overlap.

Ring of delocalised π electrons.

Electron density in the π electron cloud is significantly lower compared to an alkene π electron cloud.

Bond	Found in	Bond energy
C–C	alkane	350 kJ/mol
Carbon to carbon bond in benzene (between single and double)	benzene	520 kJ/mol
C=C	alkene	610 kJ/mol

Electrophilic Addition

Ethene, CH₂=CH₂, drawn with its π bond above and below the C–C bond, reacting with Br₂.

High electron density π bond strongly polarises Br₂.

1. A curly arrow starts from the π bond of ethene and goes to the nearer bromine atom, Br^δ+, of the polarised Br^δ+–Br^δ- molecule. A second curly arrow starts from the Br–Br bond and goes to Br^δ-. This forms the carbocation CH₂Br–CH₂⁺ and a bromide ion, Br^-.
2. A curly arrow starts from a lone pair on Br^- and goes to the positively charged carbon. This forms 1,2-dibromoethane, CH₂BrCH₂Br.

The same mechanism drawn with displayed formulae:

1. CH₂=CH₂: a curly arrow from the C=C double bond to Br^δ+ of Br^δ+–Br^δ-, and a curly arrow from the Br–Br bond to Br^δ-.
2. Carbocation intermediate, ⁺CH₂–CH₂Br: a curly arrow from the lone pair on Br^- to the C⁺.
3. Product: 1,2-dibromoethane, CH₂BrCH₂Br.

From	Reagents and conditions	To
Ethene, CH2=CH2	Br2. Br2(aq) or in an inert solvent (CCl4), r.t.p., absence of light	1,2-dibromoethane, CH2BrCH2Br (also 2-bromoethanol, CH2BrCH2OH, if aqueous)
Ethene, CH2=CH2	H2O(g). Acid catalyst H3PO4, 60 atm pressure, 300 °C	Ethanol, CH3CH2OH (the H and the OH added are circled)
Ethene, CH2=CH2	H2. Ni / Pt catalyst, 150 °C to 200 °C	Ethane, CH3CH3 (the two H atoms added are circled)
Ethene, CH2=CH2	HCl (or HBr, HI). r.t.p.	Halogenoethane, CH3CH2X. The product drawn is bromoethane, CH3CH2Br, with the H and the Br added circled

* Test for unsaturated compounds: red/orange Br₂ decolourises.

Unsaturated (smaller), low melting point → saturated (bigger), higher melting point.
(Unsaturated vegetable oil) → (margarine).

Markovnikov's Rule

Unsymmetric alkene → H gets bonded to the C in C=C which is already bonded to more H atoms. MAJOR PRODUCT.

Propene, CH₃CH=CH₂, + HBr gives two products:

• 1-bromopropane, CH₃CH₂CH₂Br (H added to the middle carbon, Br to the end carbon).
• 2-bromopropane, CH₃CHBrCH₃ (Br added to the middle carbon, H to the end carbon). Major product.

The two possible carbocations:

• CH₃CH₂CH₂⁺, 1° carbocation.
• CH₃CH⁺CH₃, 2° carbocation, stable.

Carbocations with more electron donating alkyl chains are more stable as they have a lower charge density.

Carbocation	Structure	Positive charge	Stability
1° carbocation	CH3CH2+, one CH3 group (9 electrons) pushing electrons towards C+	large	less stable
2° carbocation	(CH3)2CH+, two CH3 groups (9 electrons each) pushing electrons towards C+	small
3° carbocation	(CH3)3C+, three CH3 groups (9 electrons each) pushing electrons towards C+	very small	stable

Less stable → stable, from the 1° carbocation to the 3° carbocation.

Electrophilic Substitution

Electrophilic Substitution in Benzene

From	Reagents and conditions	To
Benzene, C6H6	Br2. AlBr3 / FeBr3 catalyst	Bromobenzene, C6H5Br, + HBr
Benzene, C6H6	Cl2. AlCl3 / FeCl3 catalyst	Chlorobenzene, C6H5Cl, + HCl
Benzene, C6H6	Conc. HNO3 + conc. H2SO4 (catalyst), T = 55 °C	Nitrobenzene, C6H5NO2

Electrophilic Substitution Mechanism

1. Bromination (or chlorination)

Drawn on the orbital diagram of benzene with the catalyst FeBr₃:

1. A curly arrow starts from the π electron cloud of benzene and goes to Br^δ+ of the Br^δ+–Br^δ- molecule. A curly arrow starts from the Br–Br bond and goes to Br^δ-, and an arrow goes from Br^δ- to the Fe of FeBr₃.
   Weak polarisation: the benzene π electron cloud has low charge density and does not repel the bonded electrons very strongly.
2. Intermediate: the ring carries a positive charge (+ drawn inside the ring) and one carbon is bonded to both Br and H. The other ion is [FeBr₄]^-, drawn as Br with a lone pair bonded to FeBr₃, in brackets with a charge of -1. A curly arrow starts from [FeBr₄]^- and goes to the H on that carbon, and a curly arrow starts from the C–H bond and goes back into the ring.

1. Products: bromobenzene, C₆H₅Br, with the ring of delocalised π electrons restored, HBr, and FeBr₃.

Exam mechanism

1. Benzene, C₆H₆: a curly arrow from the ring to Br^δ+ of Br^δ+–Br^δ-, a curly arrow from the Br–Br bond to Br^δ-, and an arrow from Br^δ- to the Fe of FeBr₃.
2. Intermediate: the ring drawn with a broken circle and a + charge, with one carbon bonded to both Br and H. A curly arrow from the lone pair on [FeBr₄]^- to the H, and a curly arrow from the C–H bond back into the ring.
3. Products: bromobenzene, C₆H₅Br, + HBr, and FeBr₃ (regenerated).

Nitration mechanism

Benzene, C₆H₆ → nitrobenzene, C₆H₅NO₂ (conc. HNO₃ + conc. H₂SO₄ (catalyst), T = 55 °C)

Conc. HNO₃ + conc. H₂SO₄ react:

HNO₃ + 2H₂SO₄ → H₃O⁺ + 2HSO₄^- + NO₂⁺

NO₂⁺: nitronium electrophile.

Drawn on the orbital diagram of benzene:

1. A curly arrow starts from the π electron cloud of benzene and goes to NO₂⁺.
2. Intermediate: the ring carries a positive charge (+ drawn inside the ring) and one carbon is bonded to both NO₂ and H. A curly arrow starts from the lone pair on HSO₄^- and goes to the H, and a curly arrow starts from the C–H bond and goes back into the ring.
3. Products: nitrobenzene, C₆H₅NO₂, with the ring of delocalised π electrons restored, + H₂SO₄. Catalyst regenerated.

Exam mechanism

1. Benzene, C₆H₆: a curly arrow from the ring to NO₂⁺.
2. Intermediate: the ring drawn with a broken circle and a + charge, with one carbon bonded to both NO₂ and H. A curly arrow from the lone pair on HSO₄^- to the H, and a curly arrow from the C–H bond back into the ring.
3. Products: nitrobenzene, C₆H₅NO₂, + H₂SO₄.

Electrophilic Substitution (2,4,6 and 3,5 Directing Groups)

Electrophilic Substitution of Benzene Derivatives

2,4(6) directing groups

1. Electrophilic Substitution of Arenes

Arene → benzene + alkyl chain.

• Ethylbenzene, C₆H₅CH₂CH₃.
• 1,3-dimethylbenzene, C₆H₄(CH₃)₂, with the CH₃ groups on carbons 1 and 3.

Printed extract: a benzene ring with a group X attached and positions 2, 3 and 4 numbered, C₆H₅X, + Y⁺ → C₆H₄XY + H⁺.

X- groups that direct the incoming Y group to the 2- or 4- positions	X- groups that direct the incoming Y group to the 3- position
–NH2, –NHR or –NR2	–NO2
–OH or –OR	–NH3+
–NHCOR	–CN
–CH3, –alkyl	–CHO, –COR
–Cl	–CO2H, –CO2R

2,4(6) directing groups are electron donating groups.

Higher charge density at positions 2, 4 (6). Electrophiles will be strongly attracted to the 2, 4, 6 positions.

Orbital diagram of propylbenzene, C₆H₅CH₂CH₂CH₃, with positions 2, 4 and 6 of the ring marked. The alkyl chain, CH₂–CH₂–CH₃, has a slight electron donating effect towards the ring.

From	Reagents and conditions	To
Methylbenzene, C6H5CH3	Br2. AlBr3 / FeBr3 catalyst	2-bromomethylbenzene and 4-bromomethylbenzene, CH3C6H4Br, + HBr
Methylbenzene, C6H5CH3	Cl2. AlCl3 / FeCl3 catalyst	2-chloromethylbenzene and 4-chloromethylbenzene, CH3C6H4Cl (drawn, not named on the page), + HCl
Methylbenzene, C6H5CH3	Conc. HNO3 + conc. H2SO4 (catalyst), T = 55 °C	2-methylnitrobenzene and 4-methylnitrobenzene, CH3C6H4NO2

Electrophilic Substitution of Phenols and Phenylamine

–OH, –NH₂: 2,4,(6) directing groups.

• Phenol, C₆H₅OH (not alcohol), with positions 2, 4 and 6 marked. The lone pair on O is drawn moving towards the ring: large electron donating effect.
• Phenylamine, C₆H₅NH₂, with positions 2, 4 and 6 marked. The lone pair on N is drawn moving towards the ring: large electron donating effect.

* Lone pair on O in the hydroxy group (or N in NH₂) overlaps with benzene's π electron cloud and significantly increases the π electron cloud density.

• Electrophiles (NO₂⁺ / Br⁺) will be strongly attracted to benzene.
• Faster reaction, milder conditions.

Halogenation

From	Reagents and conditions	To
Phenol, C6H5OH (or –NH2)	3Br2. Only Br2(aq), no catalyst needed, r.t.p.	2,4,6-tribromophenol, C6H2Br3OH (or –NH2), + 3HBr (white ppt formed)
Phenol, C6H5OH (or –NH2)	3Cl2. Only Cl2(aq), no catalyst needed, r.t.p.	2,4,6-trichlorophenol, C6H2Cl3OH (or –NH2), + 3HCl (white ppt formed)

Test for identification of phenols: red/orange Br₂(aq) decolourises and produces a white ppt.

Nitration, phenol / phenylamine

From	Reagents and conditions	To
Phenol, C6H5OH (or –NH2)	Dilute HNO3, no catalyst needed	2-nitrophenol and 4-nitrophenol, HOC6H4NO2 (or –NH2)
Phenol, C6H5OH (or –NH2)	Conc. HNO3	2,4,6-trinitrophenol, HOC6H2(NO2)3 (or –NH2) (yellow crystalline solid)

3(-5) directing groups

Electron withdrawing groups: NO₂, CHO, COOH, –NH₃⁺, CN.

Benzaldehyde, C₆H₅CHO, drawn with positions 3 and 5 marked and an arrow showing electrons drawn from the ring towards the CHO group.

Relatively higher electron density at position 3 (and 5).

Overall benzene becomes deactivated, electron density in the benzene π electron cloud is very less, less attraction for electrophiles, slower reactions / higher T / higher conc.

From	Reagents and conditions	To
Nitrobenzene, C6H5NO2	Br2 (ignore condition)	3-bromonitrobenzene, BrC6H4NO2
Nitrobenzene, C6H5NO2	Conc. HNO3 (ignore conditions)	1,3-dinitrobenzene, C6H4(NO2)2

Electrophilic Substitution : Alkylation and Acylation

Alkylation

Attach an alkyl chain to benzene.

From	Reagents and conditions	To
Benzene, C6H6	2-chloropentane, CH3CHClCH2CH2CH3. AlCl3 catalyst	(Pentan-2-yl)benzene, C6H5CH(CH3)CH2CH2CH3, + HCl
Benzene, C6H6	2-chloro-2-methylbutane, (CH3)2CClCH2CH3	(2-methylbutan-2-yl)benzene, C6H5C(CH3)2CH2CH3, + HCl

In the first reaction a curly arrow starts from the benzene ring and goes to the C^δ+ bonded to Cl, and a curly arrow starts from the C–Cl bond and goes to Cl. In the second reaction the carbon bonded to Cl is also marked δ+.

Acylation

Reaction with acyl chloride, RCOCl.

From	Reagents and conditions	To
Benzene, C6H6	Propanoyl chloride, CH3CH2COCl. AlCl3 catalyst	1-phenylpropan-1-one, C6H5COCH2CH3, + HCl

A curly arrow starts from the benzene ring and goes to the C^δ+ of the COCl group, and a curly arrow starts from the C–Cl bond and goes to Cl.

Hydrolysis of Chlorinated Compounds

Hydrolysis of Cl related compounds

Chlorobenzene	Halogenoalkanes	Acyl chloride
C6H5Cl	Chloroethane, CH3CH2Cl	Propanoyl chloride, CH3CH2COCl
NaOH(aq), heat with reflux	Vigorous reaction even with cold water. White fumes of HCl(g)

No hydrolysis → strong hydrolysis, from chlorobenzene to acyl chloride.

No Hydrolysis of Chlorobenzene

Chlorobenzene, C₆H₅Cl, drawn with the lone pairs on Cl and one lone pair overlapping with the ring. An OH^- ion and a water molecule (O^δ-) are shown approaching and being repelled.

Lone pair on Cl overlaps with benzene's π electron cloud, which increases the strength of the C–Cl bond, so the high charge density electron cloud repels OH^- ions / nucleophiles.

Negative ion is repelled by the high charge density π electron cloud.

Hydrolysis of Halogenoalkanes

1. Primary halogenoalkane, S_N2 → rate would depend on both reactants.

CH₃CH₂CH₂Cl + OH^- → CH₃CH₂CH₂OH + Cl^- (NaOH(aq), heat with reflux)

1. 1-chloropropane, CH₃CH₂CH₂Cl, with the C–Cl bond polarised C^δ+–Cl^δ-. A curly arrow starts from the lone pair on HO^- (nucleophile; also :CN^-, :NH₃) and goes to C^δ+. A curly arrow starts from the C–Cl bond and goes to Cl. This gives the transition state, in which the HO to C bond is partly formed and the C to Cl bond is partly broken (both drawn as dotted lines), with a curly arrow from the C to Cl dotted bond to Cl.
2. Products: propan-1-ol, CH₃CH₂CH₂OH, + :Cl^-.

One step mechanism.

2. Tertiary halogenoalkane, S_N1

CH₃CH₂C(CH₃)₂Cl + OH^- → CH₃CH₂C(CH₃)₂OH + Cl^- (NaOH(aq), heat with reflux)

2 step mechanism:

1. Step 1: 2-chloro-2-methylbutane, CH₃CH₂C(CH₃)₂Cl, with the C–Cl bond polarised C^δ+–Cl^δ-. A curly arrow starts from the C–Cl bond and goes to Cl. This forms the tertiary carbocation CH₃CH₂C⁺(CH₃)₂ and :Cl^-.
2. Step 2: a curly arrow starts from the lone pair on :OH^- and goes to the C⁺. This forms 2-methylbutan-2-ol, CH₃CH₂C(CH₃)₂OH, with :Cl^-.

Easier to form a tertiary carbocation. More electron donating alkyl chains lower the positive charge density.

Strong Hydrolysis of Acyl chlorides

Propanoyl chloride, CH₃CH₂COCl, drawn with C^δ+, O^δ- and Cl^δ-, and a water molecule, H₂O, with a curly arrow from the lone pair on its O to the C^δ+.

C in acyl chloride is attached to two very electronegative elements, oxygen and chlorine. So δ+ charge density is very high. Nucleophiles, H₂O:, are very strongly attracted.

CH₃CH₂COCl + H₂O → CH₃CH₂COOH + HCl (vigorous reaction even with cold water; white fumes of HCl)

Addition-Elimination Mechanism (Nucleophilic)

1. Propanoyl chloride, CH₃CH₂COCl, with C^δ+, O^δ- and Cl^δ-. A curly arrow starts from the lone pair on the O of H₂O (nucleophile) and goes to C^δ+. A curly arrow starts from the C=O double bond and goes to O^δ-.
2. Intermediate: CH₃CH₂C(O^-)(Cl)(O⁺H₂), the carbon bonded to O^-, to Cl and to the oxygen of the water molecule, which now carries a positive charge. A curly arrow starts from the lone pair on O^- and goes back to the C–O bond to reform C=O. A curly arrow starts from the C–Cl bond and goes to Cl^δ-.
3. CH₃CH₂C(=O)–O⁺H₂ and :Cl^-. A curly arrow starts from the lone pair on :Cl^- and goes to one H on the O⁺. A curly arrow starts from that O–H bond and goes to O⁺.
4. Products: propanoic acid, CH₃CH₂COOH, and HCl(g).

Comparison of Weak Acids

Weak Acids

All organic acids are weak acids (partially ionise, produce fewer H⁺ ions).

In order, from weakest acid to stronger acid:

1. alcohol, CH₃CH₂OH (weakest acid)
2. water, H₂O
3. phenol, C₆H₅OH
4. carboxylic acid, CH₃CH₂COOH (stronger acid)

Type of reaction	Reagent	Alcohol, CH3CH2OH (weak acid)	Phenol, C6H5OH	Carboxylic acid, CH3CH2COOH (strongest acid)
Redox	Reactive metal, Na	Very slow reaction. CH3CH2O-Na+ + H2	Sodium phenoxide, C6H5O-Na+ + H2	CH3CH2COO-Na+ + H2
Acid, base reactions	Strong base, NaOH	No reaction	Sodium phenoxide, C6H5O-Na+ + H2O	CH3CH2COO-Na+ + H2O
Acid, base reactions	Weak base, Na2CO3	No reaction	No reaction	CH3CH2COO-Na+ + H2O + CO2
Acid, base reactions	Weak base, NH3	No reaction	No reaction	CH3CH2COO-NH4+

Explaining acid strength

Alcohols are the weakest of the weak acids.

Ionises even less than water (water produces 1 × 10^-7 mol/dm³ H⁺ ions).

CH₃CH₂OH ⇌ CH₃CH₂O^- + H⁺

In the ethoxide ion, CH₃CH₂O^-: electron donating alkyl chain, large negative charge density on the oxygen.

The alkyl chain has an electron donating effect which increases the charge density on the CH₃CH₂O^- ion, making it unstable. Stronger attraction for H⁺ ions, less dissociation, O-H bond strength increases.

Phenols are slightly stronger acids compared to alcohols.

They can react with Na (reactive metal) and NaOH (strong bases).

C₆H₅OH ⇌ C₆H₅O^- + H⁺

In the phenoxide ion, C₆H₅O^-: a lone pair on the oxygen is drawn moving into the benzene ring. Lesser charge density on the oxygen, less attraction for H⁺. Relatively weaker conjugate base.

Lone pairs on the phenoxide ion, C₆H₅O^-, overlap with benzene's pi electron cloud. Charge density on the phenoxide ion decreases, making it more stable (less attraction for H⁺, the O-H bond weakens), hence more dissociation.

Comparison of acid strength within phenols

Phenol, C₆H₅OH, versus 4-propylphenol, CH₃CH₂CH₂C₆H₄OH.

Phenol	Ion formed	Notes
phenol, C6H5OH	C6H5O- + H+
4-propylphenol, CH3CH2CH2C6H4OH	CH3CH2CH2C6H4O- + H+	The CH3CH2CH2 group has an electron donating effect. Negative charge density is higher, unstable, stronger O-H bond, dissociates less / weaker.

Phenol, C₆H₅OH, versus 4-nitrophenol, shown as its ion O₂NC₆H₄O^- + H⁺.

The O₂N group is electron withdrawing. Negative charge density is lesser, more stable, less attraction for H⁺ ions, O-H bond becomes weaker.

Why are carboxylic acids (relatively) the strongest acid

CH₃CH₂COOH ⇌ CH₃CH₂COO^- + H⁺

The negative charge density on the O^- is small. An arrow is drawn from the O^- towards the C=O, and the ion is then drawn as CH₃CH₂COO^- with the negative charge spread over both oxygens.

In carboxylic acids, a highly electronegative oxygen in C=O has a strong electron withdrawing effect, which decreases the negative charge density in the RCOO^- ion, making it stable. Less attraction for H⁺ ions, O-H bond strength decreases, more dissociation / relatively strong acid.

Alkyl chain length → carboxylic acid strength

Ethanoate ion, CH₃COO^- + H⁺: the CH₃ group donates electrons.

Butanoate ion, CH₃CH₂CH₂COO^- + H⁺: electron donating effect of the longer chain, larger charge density on the O^-, more attraction for H⁺.

Large electron donating effect in bigger alkyl chains.

Higher negative charge density in RCOO^-, making it unstable. More attraction for H⁺ ions, stronger O-H bond, less ionisation → weaker acid.

Cl substituted carboxylic acid

More Cl, stronger acid (going down the list):

1. Ethanoate ion, CH₃COO^- + H⁺.
2. Chloroethanoate ion, ClCH₂COO^- + H⁺: Cl pulls electrons away from the COO^-, lesser charge density, less attraction for H⁺.
3. Trichloroethanoate ion, CCl₃COO^- + H⁺: even lesser charge density, even less attraction for H⁺.

Cl has an electron withdrawing effect. RCOO^- charge density decreases, becomes more stable, O-H is weaker, less attraction for H⁺ → stronger acid, more ionisation.

Position of Cl

3-chloropropanoate ion, ClCH₂CH₂COO^- + H⁺: the Cl is further from the COO^-.

2-chloropropanoate ion, CH₃CHClCOO^- + H⁺: smaller charge density on the O^-. Stronger acid.

Cl is closer, more electron withdrawing effect. RCOO^- becomes more stable, lower charge density, less attraction for H⁺. O-H bond becomes weaker → more dissociation.

Comparison of Weak Bases

Strength of bases (all are weak)

Nitrogen bases accept H⁺ ions.

NH₃ + H⁺ → [NH₄]⁺ (the lone pair on N forms a dative bond to the H⁺)

In order, from not basic to strongly basic:

1. amides, for example CH₃CONHCH₃ (not basic)
2. phenylamine, C₆H₅NH₂
3. ammonia, NH₃
4. ethylamine, CH₃CH₂NH₂ (strongly basic)

Compound	Basicity	Explanation
Amides, CH3CONHCH3	Not basic	The lone pair on N in the amide overlaps with the π electron cloud in C=O, as oxygen has a strong electron withdrawing effect. The lone pair on N is not available to accept H+ ions.
Phenylamine, C6H5NH2	Weakly basic	The lone pair on N overlaps with benzene's π electron cloud and its charge density decreases. Hence weaker attraction for H+ ions, weakly basic. C6H5NH2 + HCl → C6H5NH3+ (phenylammonium ion) + Cl-
Ethylamine, CH3CH2NH2	Strongly basic	The alkyl chain has an electron donating effect. Charge density on the lone pair on N increases, more attraction for H+ ions, stronger base.

All Redox Reactions (Including AS)

Redox Reactions

Hydrogenation of benzene

benzene, C₆H₆ → cyclohexane, C₆H₁₂ (H₂(g), Ni / Pt catalyst, 150 °C)

Oxidation of Arenes

1-ethyl-3-methylbenzene, CH₃C₆H₄CH₂CH₃ → benzene-1,3-dicarboxylic acid, HOOCC₆H₄COOH (KMnO₄ / H⁺ + heat, reflux)

Oxidation of Alkenes

1. Mild oxidation

propene, CH₃CH=CH₂ → propane-1,2-diol, CH₃CH(OH)CH₂OH (cold / dilute KMnO₄)

2. Strong oxidation (hot, concentrated, acidified KMnO₄)

The C=C bond is broken.

From	To
(a)	=CH2	CO2 + H2O
(b)	=CHR	RCHO (aldehyde) → RCOOH (carboxylic acid)
(c)	=CR2	R2C=O

Examples:

• 2-methylbut-2-ene, (CH₃)₂C=CHCH₃ → propanone, (CH₃)₂C=O, and ethanoic acid, CH₃COOH.
• 1-methylcyclohexene → the ring opens at the C=C to give 6-oxoheptanoic acid, CH₃CO(CH₂)₄COOH.
• 3,4-dimethylpenta-1,3-diene, (CH₃)₂C=C(CH₃)CH=CH₂ (as read from the sketch) → propanone, (CH₃)₂C=O, and 2-oxopropanoic acid, CH₃COCOOH, and CO₂ + H₂O.

Primary Alcohol → aldehyde → carboxylic acid

Primary alcohol (propan-1-ol, CH₃CH₂CH₂OH) → oxidation → aldehyde → oxidation → carboxylic acid.

From	Reagents and conditions	To	Type of reaction
Primary alcohol	1. K2Cr2O7 / H+, reflux, heat. Orange to green. 2. KMnO4 / H+, reflux, heat. Purple to colourless.	Aldehyde	Oxidation
Aldehyde	1. K2Cr2O7 / H+, reflux, heat. Orange to green. 2. KMnO4 / H+, reflux, heat. Purple to colourless. 3. Tollens' reagent, [Ag(NH3)2]+. Silver mirror / black ppt. 4. Fehling's reagent + heat. Cu2+ → Cu2O, brick red ppt of copper(I) oxide.	Carboxylic acid	Oxidation

To stop at the aldehyde and prevent further reaction: not reflux → distillation.

Aldehydes have much lower melting and boiling points as they don't form hydrogen bonds, and they evaporate easily.

Only two carboxylic acids are oxidised.

Most carboxylic acids are resistant to oxidation.

1. Methanoic acid, HCOOH → CO₂ + H₂O, with any of:

1. K₂Cr₂O₇ / H⁺ / reflux
2. KMnO₄ / H⁺ / reflux
3. Tollens' reagent, [Ag(NH₃)₂]⁺
4. Fehling's solution + heat

2. Ethanedioic acid (oxalic acid), HOOCCOOH → CO₂ + H₂O (KMnO₄ / H⁺, reflux)

Secondary Alcohols → Ketones

From	Reagents and conditions	To	Type of reaction
Secondary alcohol, R2CHOH	1. K2Cr2O7 / H+, reflux, heat. Orange to green. 2. KMnO4 / H+, reflux, heat. Purple to colourless.	Ketone, R2C=O	Oxidation

Tertiary alcohols

No oxidation.

Example

1-(hydroxymethyl)cyclohexane-1,3-diol (a cyclohexane ring where carbon 1 carries an OH and a CH₂OH group, and carbon 3 carries an OH) → 1-hydroxy-3-oxocyclohexane-1-carboxylic acid (acidified K₂Cr₂O₇, reflux)

• The OH on carbon 1 of the ring is a tertiary alcohol: no change.
• The CH₂OH group is a primary alcohol: becomes a carboxylic acid, COOH.
• The OH on carbon 3 of the ring is a secondary alcohol: becomes a ketone, C=O.

Reduction

From	Reagents and conditions	To
Carboxylic acid	LiAlH4 (lithium hydrido aluminate)	Aldehyde
Aldehyde	LiAlH4 / NaBH4	Primary alcohol
Ketones	LiAlH4 / NaBH4	Secondary alcohol

Reduction of Nitrobenzene

nitrobenzene, C₆H₅NO₂ → phenylamine, C₆H₅NH₂ (Sn + conc. HCl + heat)

Reduction of Amides

amide, RCONHR → amine, RCH₂NHR (LiAlH₄). The C=O becomes CH₂: loses O, gains 2H.

Reduction of nitriles

nitrile, RC≡N → alkyl amine, RCH₂NH₂ (H₂ + Ni catalyst, 150 °C, or LiAlH₄)

Dye Stuff : Azo Dyes

Dye Stuff / Azo Dyes

"Paints" → azo dyes are very stable.

From	Reagents and conditions	To	Type of reaction
benzene, C6H6	conc. HNO3, conc. H2SO4, T = 55 °C	nitrobenzene, C6H5NO2	Electrophilic substitution
nitrobenzene, C6H5NO2	Sn + conc. HCl + heat	phenylamine, C6H5NH2
phenylamine, C6H5NH2	NaNO2 + HCl (HNO2), T < 10 °C	diazonium ion, C6H5N2+Cl- (C6H5–N+≡N Cl-), an electrophile, very unstable
diazonium ion, C6H5N2+Cl-	hydrolysis, decomposes if T > 10 °C, H2O	phenol, C6H5OH + N2

Azo dye formation

The diazonium ion electrophile attacks an activated benzene (benzene + OH / NH₂, electron donating).

1. The lone pair on the oxygen of phenol, C₆H₅OH, is drawn into the ring, so the ring is activated (shown shaded as electron rich).
2. A curly arrow goes from the activated ring of phenol to the end nitrogen of the diazonium ion, C₆H₅–N⁺≡N. Conditions: T < 10 °C, NaOH(aq).
3. The product is C₆H₅–N=N–C₆H₄–OH (4-hydroxyazobenzene, with the OH opposite the N=N). The –N=N– is the azo group.

Just as an Example

Printed chart of dye structures, with the –N=N– azo group highlighted in each azo dye:

Dye	Type
Acid Red 27	azo dye
Disperse Red 60	anthraquinone dye
Direct Blue 86	phthalocyanine dye
Disperse Blue 60	anthraquinone dye
Acid Orange 7	azo dye
Direct Green 1	azo dye

Find original reactants

Acid Orange 7 (azo dye): Na^{+ -}O₃S–C₆H₄–N=N–C₁₀H₆–OH, a benzene ring carrying a sodium sulfonate group, joined through the azo group to a naphthalene ring system that carries an OH next to the azo group.

–N⁺≡N, that comes from the inactive benzene.

The molecule is split by a line drawn next to the N=N, on the side of the ring that carries the OH. The two original reactants are:

• the diazonium ion, Na^{+ -}O–S(=O)₂–C₆H₄–N⁺≡N (a benzene ring with the sodium sulfonate group opposite the diazonium group)
• naphthalen-2-ol, C₁₀H₇OH (two fused benzene rings with an OH group)

Formation of Acyl Chlorides

Acyl chlorides

R–C(=O)–Cl, written RCOCl.

Formation

From	Reagents and conditions	To
carboxylic acid, R–C(=O)–OH	PCl3 + heat SOCl2 + heat PCl5 (+ heat)	acyl chloride, R–C(=O)–Cl

3CH₃COOH + PCl₃ → 3CH₃COCl + H₃PO₃

CH₃COOH + PCl₅ → CH₃COCl + HCl + POCl₃

CH₃COOH + SOCl₂ → CH₃COCl + SO₂ + HCl

Esters & Amides

Formation of Esters

1. Alcohol + carboxylic acid ⇌ ester + H₂O

• Forward reaction: addition-elimination, "condensation". Conc. H₂SO₄ + reflux.
• Reverse reaction: dilute H₂SO₄ / NaOH, reflux (acid or alkaline hydrolysis).

CH₃CH₂OH + CH₃CH₂COOH ⇌ CH₃CH₂COOCH₂CH₃ + H₂O

1. A curly arrow goes from the lone pair on the oxygen of the alcohol, CH₃CH₂OH, to the δ+ carbon of the C=O in the acid, CH₃CH₂COOH.
2. The OH of the acid and the H of the alcohol's OH are crossed out. They leave as H₂O.
3. The product is CH₃–CH₂–C(=O)–O–CH₂–CH₃ + H₂O. The –C(=O)–O– is the ester link.

Naming: the CH₃CH₂C(=O)– part is "propanoate" and the –CH₂CH₃ part is "ethyl", so the ester is ethyl propanoate.

A diol with two carboxylic acids:

1. Reactants: carboxylic acid, 2-methylpropanoic acid, (CH₃)₂CHCOOH, on each side of a diol, ethane-1,2-diol, HOCH₂CH₂OH.
2. The OH of each carboxylic acid and the H of each OH on the diol are crossed out.
3. Product: (CH₃)₂CHCOOCH₂CH₂OOCCH(CH₃)₂, with an ester group at each end of the diol.

Forming a ring:

1. Two molecules of 4-hydroxybutanoic acid, HOCH₂CH₂CH₂COOH, are drawn facing each other, the OH end of one next to the COOH end of the other.
2. At both places the OH of the COOH and the H of the alcohol OH are crossed out.
3. Product: a ring containing two ester groups, –O–CH₂CH₂CH₂–C(=O)–O–CH₂CH₂CH₂–C(=O)– joined end to end (a cyclic diester).

Alkaline hydrolysis of Esters produces soaps

The ester R–C(=O)–O–R is split between the C of the C=O and the O:

• R–C(=O)–OH, which reacts with alkali to give R–C(=O)–O^- Na⁺
• R–OH

Acyl chlorides + alcohols → Ester + HCl

Fast vigorous reaction, no conditions needed.

RCOCl + R–OH → RCOOR + HCl

1. A curly arrow goes from the lone pair on the oxygen (δ-) of the alcohol, H–O–R, to the δ+ carbon of the C=O in the acyl chloride, R–C(=O)–Cl.
2. The Cl of the acyl chloride and the H of the alcohol are circled together. They leave as HCl.
3. The product is the ester R–C(=O)–O–R + HCl.

Phenols only form Esters with acyl chlorides

RCOCl + C₆H₅OH → RCOOC₆H₅ + HCl

1. The carbon of the C=O in the acyl chloride, R–C(=O)–Cl, is δ+ with a high charge density.
2. A curly arrow goes from the lone pair on the oxygen of phenol, H–O–C₆H₅, to this δ+ carbon. A second small arrow shows the lone pair on the oxygen moving towards the benzene ring.
3. The product is the ester R–C(=O)–O–C₆H₅ + HCl.

The lone pair on phenol overlaps with the benzene pi electron cloud, unavailable for ester formation with carboxylic acid.

Acyl chlorides form amides with phenylamine

RCOCl + C₆H₅NH₂ → RCONHC₆H₅ + HCl

1. A curly arrow goes from the lone pair on the nitrogen of phenylamine, C₆H₅NH₂, to the δ+ carbon of the C=O in the acyl chloride, R–C(=O)–Cl. A second small arrow shows the lone pair on the nitrogen moving towards the benzene ring.
2. The Cl of the acyl chloride and one H on the nitrogen are circled together. They leave as HCl.
3. The product is R–C(=O)–N(H)–C₆H₅ + HCl. The –C(=O)–N(H)– group is boxed and labelled amide.

With a secondary amine:

RCOCl + CH₃NHCH₂CH₃ → RCON(CH₃)CH₂CH₃ + HCl

1. A curly arrow goes from the lone pair on the nitrogen of the secondary amine, CH₃–NH–CH₂–CH₃, to the δ+ carbon of the C=O in R–C(=O)–Cl.
2. The Cl and the H on the nitrogen are circled together. They leave as HCl.
3. The product is R–C(=O)–N(CH₃)–CH₂–CH₃ + HCl.

With a primary amine:

RCOCl + CH₃CH₂NH₂ → RCONHCH₂CH₃ + HCl

1. A curly arrow goes from the lone pair on the nitrogen of the primary amine, H₂N–CH₂–CH₃, to the δ+ carbon of the C=O in R–C(=O)–Cl.
2. The Cl and one H on the nitrogen are circled together. They leave as HCl.
3. The product is R–C(=O)–N(H)–CH₂–CH₃ + HCl.

Acid / alkaline hydrolysis of amides

The amide R–C(=O)–N(H)–R is split between the C of the C=O and the N:

• R–C(=O)–OH (alkaline hydrolysis: R–C(=O)–O^- Na⁺)
• H–N(H)–R, which is RNH₂ (acid hydrolysis → RNH₃⁺)

Amino Acids, Polymerisation

Amino Acids

Amino acids (monomer) → Protein (polymer)

General structure: H₂N–CH(R)–COOH. The NH₂ group and the COOH group are circled. Only the R is different.

• alanine, H₂N–CH(CH₃)–COOH
• valine, H₂N–CH(CH(CH₃)₂)–COOH
• H₂N–CH(CH₂COOH)–COOH (not named on the page; this is aspartic acid)
• H₂N–CH((CH₂)₄NH₂)–COOH (not named on the page; this is lysine)

Primary Structure / simple polypeptide (Condensation Polymers)

1. Four amino acids are drawn in a row: alanine, H₂N–CH(CH₃)–COOH, then valine, H₂N–CH(CH(CH₃)₂)–COOH, then H₂N–CH(CH₂COOH)–COOH, then H₂N–CH((CH₂)₄NH₂)–COOH.
2. Between each pair, the OH of one COOH group and an H of the next NH₂ group are circled together.
3. Condensation polymer: the circled atoms are removed and the C of each C=O joins to the N of the next amino acid, giving H₂N–CH(CH₃)–C(=O)–N(H)–CH(CH(CH₃)₂)–C(=O)–N(H)–CH(CH₂COOH)–C(=O)–N(H)–CH((CH₂)₄NH₂)–COOH.

–C(=O)–N(H)– is the amide / peptide link.

Condensation Polymerisation

1. Polyester

From a diacyl chloride and a diol (□ stands for the rest of each molecule):

1. The monomers are drawn alternately: diacyl chloride, Cl–C(=O)–□–C(=O)–Cl, then diol, HO–□–OH, then diacyl chloride, then diol.
2. A curly arrow goes from the lone pair on an oxygen of the diol to the δ+ carbon of a C=O in the diacyl chloride.
3. Each Cl of the diacyl chloride and each H of the diol's OH groups are crossed out.
4. Condensation gives the chain –C(=O)–□–C(=O)–O–□–O–C(=O)–□–C(=O)–O–□–O– + HCl + HCl + HCl. The –C(=O)–O– group (boxed) is the ester linkage.

From a dicarboxylic acid and a diol:

1. The monomers are drawn alternately: dicarboxylic acid, HO–C(=O)–□–C(=O)–OH, then diol, HO–□–OH, then dicarboxylic acid, then diol.
2. Each OH of the dicarboxylic acid and each H of the diol's OH groups are crossed out.
3. Condensation gives the chain –C(=O)–□–C(=O)–O–□–O–C(=O)–□–C(=O)–O–□–O– + H₂O + H₂O + H₂O. The –C(=O)–O– group (boxed) is the ester linkage.

Repeat unit: –[C(=O)–O–□–O–C(=O)–□]–_n

Examples

• Terylene, fabric, clothing
• natural polyesters, fats

Printed diagram of a fat: glycerol joined through three –O–C(=O)– groups to three long fatty acid chains, one of which contains a C=C double bond. Key: glycerol, carboxyl group, fatty acid, double bond.

2. Polyamide

1. The monomers are drawn alternately: diacyl chloride (or dicarboxylic acid), Cl–C(=O)–□–C(=O)–Cl, then diamine, H₂N–□–NH₂, then diacyl chloride, then diamine.
2. A curly arrow goes from the lone pair on a nitrogen of the diamine to the δ+ carbon of a C=O in the diacyl chloride.
3. Each Cl of the diacyl chloride and one H on each nitrogen of the diamine are crossed out.
4. Condensation / addition-elimination gives the chain –C(=O)–□–C(=O)–N(H)–□–N(H)–C(=O)–□–C(=O)–N(H)–□–N(H)– + HCl + HCl + HCl. The –C(=O)–N(H)– group (boxed) is the amide linkage.

Repeat unit: –[N(H)–C(=O)–□–C(=O)–N(H)–□]–_n

Examples

Kevlar, Nylon, natural proteins.

Addition Polymers

monomer = alkene

Propene, CH₃–CH=CH₂. The C=C is boxed. The CH₃ group and the H at the two ends are circled, with arrows showing them redrawn below the C=C carbons.

1. Five propene molecules are drawn side by side, each as C(H)(CH₃)=C(H)(H) with the CH₃ and one H drawn below the C=C.
2. Addition: each C=C becomes C–C and the molecules join to each other, giving the chain –CH(CH₃)–CH₂–CH(CH₃)–CH₂–CH(CH₃)–CH₂–CH(CH₃)–CH₂–CH(CH₃)–CH₂–, polypropene.

Repeat unit: –[CH(CH₃)–CH₂]–_n

Addition Polymers vs Condensation Polymers

Addition Polymers	Condensation Polymers
inert, non biodegradable	very polar linkages: –C(=O)–O– and –C(=O)–N(H)–, with the C δ+, the O of the C=O δ- and the N δ-
PVC, Polyethene, Polypropene	very reactive, hydrolyse easily
linkage → non-polar carbon chain, very stable and unreactive	heat / boil with dilute acid or dilute alkali