Organic Chemistry

Question 1

Functional group

Answer 1

A specific atom/group of atoms that determines the chemical properties and reactions of a molecule.

Question 2

Homologous series

Answer 2

A series of organic compounds with the same functional group and general formula, differing by CH₂ units.

Question 3

Nomenclature Rules (IUPAC):

Answer 3

1. Identify the longest carbon chain.
   
   2. Number the chain giving substituents the lowest possible numbers.
   3. Name and order substituents alphabetically with position numbers.

Question 4

Types of Organic Compounds:

Answer 4

Alkanes – CₙH₂ₙ₊₂, saturated. hydrocarbons.

Alkenes – CₙH₂ₙ, contain C=C double bond.

Haloalkanes – contain halogen atoms.
Alcohols – contain –OH group.
Aldehydes – contain terminal –CHO group.

Ketones – contain internal C=O group.
Carboxylic acids – contain –COOH group.

Esters, Amines, Amides appear in A2 content.

Question 5

Structural isomers

Answer 5

same molecular formula, different structural arrangement.
Eg Chain isomers
• Position isomers
• Functional group isomers

Question 6

Stereoisomers

Answer 6

• compounds that have the same atoms connected to each other, however the atoms are differently arranged in space

• E/Z nomenclature is used to distinguish between the isomers
- Z isomers have functional groups on the same side of the double bond/carbon ring
- E isomers have functional groups on opposite sides of the double bond/carbon ring

Question 7

Optical Isomerism (A2):

Answer 7

chiral centres produce enantiomers.

Question 8

Alkanes

Answer 8

• are active due to strong sigma bonds. —-Combustion:
  • Complete: produces CO₂ and H₂O.
  • Incomplete: produces CO and/or C (soot), dangerous in enclosed spaces.
  • Free Radical Substitution (e.g. Chlorination):
  • Requires UV light.
  • Initiation: Cl₂ → 2Cl•
  • Propagation: Cl• + CH₄ → HCl + CH₃•, CH₃• + Cl₂ → CH₃Cl + Cl•
  • Termination: 2Cl• → Cl₂, CH₃• + Cl• → CH₃Cl, CH₃• + CH₃• → C₂H₆

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Question 9

Alkenes

Answer 9

• Electrophilic Addition Reactions:
• π bond is electron-rich → attacks electrophiles.
• Reactions: with HBr, H₂ (Ni catalyst), Br₂ (test for unsaturation), steam (H₃PO₄ catalyst).
• Mechanism Example: Ethene + HBr
1. Electrophile (Hδ⁺) attracted to π electrons.
2. Carbocation intermediate formed.
3. Nucleophile (Br⁻) attacks carbocation.
• Markovnikov’s Rule: more stable carbocation intermediate forms preferentially.
• Addition Polymerisation: Monomers join to form polymers like poly(ethene).

Question 10

What are the three types of structural isomerism?

Answer 10

1. Chain isomerism – different carbon chain arrangement
   
   2. Position isomerism – same functional group in different positions
   3. Functional group isomerism – different functional groups

Question 11

What is the test for alkenes?

Answer 11

Bromine water turns orange to colourless due to electrophilic addition across the double bond.

Question 12

What is the mechanism for alkene + HBr?

Answer 12

Electrophilic addition:
• H⁺ adds to the carbon with most H (Markovnikov’s Rule)
• Forms the most stable carbocation intermediate

Question 13

What are the two steps in the reaction of a halogenoalkane with OH⁻?

Answer 13

Nucleophilic substitution: OH⁻ attacks δ⁺ carbon
• Halide ion leaves, forming alcohol

Question 14

What is the trend in reactivity of halogenoalkanes?

Answer 14

Increases down the group: C–I bond is weakest, so more easily broken.

Question 15

What are the two types of alcohol oxidation reactions?

Answer 15

• Primary alcohols → Aldehydes → Carboxylic acids
• Secondary alcohols → Ketones
• Tertiary alcohols: Do not oxidise

Question 16

Reagent and condition for alcohol oxidation?

Answer 16

• Reagent: Acidified potassium dichromate (K₂Cr₂O₇ / H₂SO₄)
• Orange to green colour change

Question 17

How are esters formed?

Answer 17

Esterification:
Carboxylic acid + alcohol → ester + water (in presence of conc. H₂SO₄)

Question 18

What is hydrolysis of esters?

Answer 18

Acid hydrolysis: Ester + water → carboxylic acid + alcohol
• Base hydrolysis: Ester + NaOH → carboxylate salt + alcohol

Question 19

What is infrared spectroscopy used for?

Answer 19

Identifying functional groups based on bond absorption of IR radiation.

Question 20

What does a peak at ~1700 cm⁻¹ in an IR spectrum indicate?

What does a broad peak at 3200–3550 cm⁻¹ in IR suggest?

Answer 20

Presence of a C=O group (carbonyl) - common to carbonyl compounds like aldehydes, ketones, esters, and acids.

Presence of an O–H group (alcohol); broad and smooth peak..

Question 21

What is the fingerprint region in IR spectroscopy?

Answer 21

500–1500 cm⁻¹; unique to each compound but often too complex for identification.

Question 22

How is a carboxylic acid O–H distinguished in IR?

Answer 22

Very broad, rough peak from 2500–3300 cm⁻¹; usually overlaps with C–H region.

Question 23

What is the equation for the natural formation of ozone in the stratosphere?

Answer 23

O₂ → 2O· (via UV light)
O· + O₂ → O₃

Question 24

What is the equation for the natural breakdown of ozone?

Answer 24

O₃ → O₂ + O· (via UV light)
O· + O₃ → 2O₂

Question 25

What are CFCs and why are they harmful?

Answer 25

Chlorofluorocarbons are stable compounds that release chlorine radicals in the upper atmosphere, catalytically destroying ozone.

Question 26

Write the initiation ,propagation and overall step for ozone depletion by CFCs.

Answer 26

CCl₃F → CCl₂F· + Cl· (via UV radiation) Cl· + O₃ → ClO· + O₂ ClO· + O· → Cl· + O₂ O₃ + O· → 2O₂ (Chlorine radical is regenerated and acts as a catalyst.)

Question 27

What are HFCs and why are they better than CFCs?

Answer 27

Hydrofluorocarbons contain no chlorine, so they don’t release ozone-destroying radicals in the stratosphere.

Question 28

What type of bond allows alkenes to polymerise?

Answer 28

The C=C double bond, which is reactive and can open up to form new covalent bonds with other monomers.

Question 29

What are the conditions for addition polymerisation?

Answer 29

High pressure and temperature, with catalysts (varies depending on polymer type).

Question 30

Why do polyalkenes have high melting points?

Answer 30

Due to strong Van der Waals or dipole–dipole forces between long chains, requiring more energy to break.

Question 31

Why are plasticisers added to polymers?

Answer 31

To make polymers softer and more flexible by reducing intermolecular forces between chains.

Question 32

What are the two main industrial methods for producing ethanol?

Answer 32

1. Hydration of ethene (industrial, non-renewable) 2. Fermentation of glucose (renewable, biological)

Question 33

What are the conditions for the hydration of ethene?

Answer 33

• 300°C • 60–70 atm • Phosphoric acid catalyst (H₃PO₄) • Continuous process Hydration of ethene is faster — continuous and fast Atom economy; 100% atom economy

Question 34

What conditions are required for fermentation?

Answer 34

• 30–40°C • Anaerobic conditions • Yeast enzyme catalyst • Batch process Atom economy- Lower (CO₂ is a by-product) Fermentation produces aqueous ethanol that must be fractionally distilled.

Question 35

What is formed when an alcohol undergoes elimination? What are the conditions for dehydration of alcohols? Why does elimination of alcohols sometimes give a mixture of alkenes?

Answer 35

An alkene and water. Conc. H₂SO₄ or H₃PO₄ catalyst • Heat under reflux Due to carbocation rearrangements and stability of alkenes (more substituted alkenes are more stable).

Question 36

What are the conditions for elimination from halogenoalkanes? What are the products of elimination from a halogenoalkane

Answer 36

Hot ethanolic KOH • Reflux An alkene, HBr (or HX), and KX (or NaX)

Question 37

What is Markownikoff’s rule ?

Answer 37

When a hydrogen halide reacts with an asymmetric alkene, the hydrogen atom of the hydrogen halide is more likely to bond to the carbon atom which is attached to the greater number of hydrogen atoms.