Organic

Question 1

Define homologous series.

Answer 1

A family of compounds with the same functional group, similar chemical properties, and a trend in physical properties due to increasing chain length.

Question 2

What is structural isomerism?

Answer 2

Compounds with the same molecular formula but different structural arrangements (e.g., chain, positional, functional group isomers).

Question 3

Write the general formula for alkanes.

Answer 3

CₙH₂ₙ₊₂.

Question 4

What reaction occurs when alkanes combust completely?

Answer 4

Alkane + O₂ → CO₂ + H₂O (+ energy).

Question 5

Describe the mechanism for free radical substitution (e.g., methane + Cl₂).

Answer 5

Initiation (Cl₂ → 2Cl•), Propagation (CH₄ + Cl• → CH₃• + HCl; CH₃• + Cl₂ → CH₃Cl + Cl•), Termination (radicals combine).

Question 6

What is electrophilic addition?

Answer 6

A double bond opens, with an electrophile (e.g., H⁺) attacking first, forming a carbocation intermediate.

Question 7

Draw the mechanism for bromine (Br₂) reacting with propene.

Answer 7

Br₂ polarizes → cyclic bromonium ion forms → Br⁻ attacks carbocation → 1,2-dibromopropane.

Question 8

What is Markovnikov’s rule?

Answer 8

The electrophile adds to the carbon with the most H atoms, forming the most stable carbocation.

Question 9

How do you test for an alkene?

Answer 9

Bromine water turns from orange to colorless.

Question 10

What are addition polymers? Give an example.

Answer 10

Long chains formed by repeated addition of monomers (e.g., polyethene from ethene).

Question 11

Compare SN1 and SN2 mechanisms.

Answer 11

SN1: Two steps (carbocation intermediate), tertiary substrates. SN2: One step (backside attack), primary substrates.

Question 12

What conditions favor elimination over substitution?

Answer 12

Ethanolic NaOH, heat.

Question 13

Why are CFCs harmful?

Answer 13

They catalyze ozone depletion via Cl• radicals.

Question 14

Write the equation for hydrolysis of 1-bromopropane with NaOH.

Answer 14

CH₃CH₂CH₂Br + NaOH → CH₃CH₂CH₂OH + NaBr.

Question 15

What is a nucleophile?

Answer 15

Electron-rich species (e.g., OH⁻, CN⁻) that donates a pair of electrons.

Question 16

How is ethanol produced industrially?

Answer 16

Fermentation (yeast, 30–40°C) or hydration of ethene (H₃PO₄ catalyst, 300°C).

Question 17

What reagent oxidizes a primary alcohol to a carboxylic acid?

Answer 17

Acidified K₂Cr₂O₇ under reflux.

Question 18

What is dehydration of ethanol?

Answer 18

Heating with concentrated H₂SO₄ → ethene + H₂O.

Question 19

What is the Lucas test?

Answer 19

Differentiates primary, secondary, and tertiary alcohols by reaction speed with HCl/ZnCl₂.

Question 20

Draw the structure of a secondary alcohol.

Answer 20

OH group attached to a carbon bonded to two alkyl groups (e.g., propan-2-ol).

Question 21

How is a ketone distinguished from an aldehyde?

Answer 21

Tollens’ reagent: Aldehyde forms a silver mirror; ketone does not.

Question 22

Write the mechanism for nucleophilic addition of HCN to propanal.

Answer 22

CN⁻ attacks δ⁺C=O → intermediate → protonation → hydroxynitrile.

Question 23

What is the iodoform reaction?

Answer 23

Identifies CH₃CO- or CH₃CH(OH)- groups using I₂/NaOH → yellow precipitate (CHI₃).

Question 24

How is a carboxylic acid produced from a nitrile?

Answer 24

Hydrolysis with HCl/H₂O (reflux) → carboxylic acid + NH₄⁺.

Question 25

What is esterification?

Answer 25

Carboxylic acid + alcohol ⇌ ester + H₂O (H₂SO₄ catalyst).

Question 26

Why is benzene resistant to addition reactions?

Answer 26

Delocalized π-electrons stabilize the ring, making electrophilic substitution favorable.

Question 27

Write the equation for nitration of benzene.

Answer 27

C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O (H₂SO₄ catalyst, 50°C).

Question 28

What is Friedel-Crafts acylation?

Answer 28

Benzene + acyl chloride → aryl ketone (AlCl₃ catalyst).

Question 29

What is a directing group? Give an example.

Answer 29

Groups that guide substitution to specific positions (e.g., -NO₂ meta-directs).

Question 30

Why are phenols more reactive than benzene?

Answer 30

-OH group donates electrons into the ring, activating it.

Question 31

What IR absorption indicates an -OH group?

Answer 31

Broad peak ~3200–3600 cm⁻¹ (alcohols: ~3300; carboxylic acids: ~2500–3300).

Question 32

How does mass spectrometry determine molecular mass?

Answer 32

Molecular ion (M⁺) peak gives the Mr.

Question 33

What does a triplet in ¹H NMR indicate?

Answer 33

Adjacent to two equivalent protons (n+1 rule).

Question 34

What chemical shift indicates a carbonyl group?

Answer 34

~1680–1750 cm⁻¹ (IR) or δ 2.1–3.0 ppm (¹H NMR for ketones).

Question 35

How is TMS used in NMR?

Answer 35

Reference peak at δ 0 ppm (inert, volatile).

Question 36

How are amines produced from nitriles?

Answer 36

Reduction with H₂/Ni catalyst → primary amine.

Question 37

Why are amines basic?

Answer 37

Lone pair on N accepts protons (e.g., CH₃NH₂ + H⁺ → CH₃NH₃⁺).

Question 38

What is a condensation polymer? Give an example.

Answer 38

Formed by monomers linking with loss of small molecule (e.g., polyester: diol + dicarboxylic acid).

Question 39

Compare addition and condensation polymers.

Answer 39

Addition: One monomer, no byproduct (e.g., polyethene). Condensation: Two monomers, byproduct (e.g., H₂O).

Question 40

What is hydrolysis of polyesters?

Answer 40

Breaking ester bonds with acid/base → original monomers.

Question 41

What is a zwitterion?

Answer 41

A molecule with both +ve (NH₃⁺) and -ve (COO⁻) charges (e.g., amino acids at pH 7).

Question 42

Draw a peptide bond.

Answer 42

-CO-NH- formed by condensation.

Question 43

How does DNA structure enable replication?

Answer 43

Complementary base pairing (A-T, C-G) via hydrogen bonds.

Question 44

What is gel electrophoresis used for?

Answer 44

Separating DNA fragments by size.

Question 45

What bonds stabilize protein tertiary structure?

Answer 45

Ionic, disulfide, hydrogen, and hydrophobic interactions.

Question 46

Outline steps to synthesize aspirin from salicylic acid.

Answer 46

Salicylic acid + ethanoic anhydride → aspirin (H₂SO₄ catalyst, reflux).

Question 47

What does a D₂O shake do in NMR?

Answer 47

Removes -OH/-NH peaks by exchanging H with D.

Question 48

How many proton environments are in CH₃CH₂COCH₃?

Answer 48

3: CH₃, CH₂, COCH₃.

Question 49

What is retrosynthesis?

Answer 49

Planning synthesis backward from target molecule to simple precursors.

Question 50

How do you calculate atom economy?

Answer 50

(Mr of desired product / ΣMr of all reactants) × 100.