Free radical reactions generally involve
A heterolytic bond cleavage
B homolytic bond cleavage
C ionic intermediates
D carbocation formation only
Free radicals are formed by equal splitting of a covalent bond.
A free radical is a species having
A positive charge
B negative charge
C unpaired electron
D paired electrons
Presence of an unpaired electron makes it highly reactive.
Free radical halogenation of alkanes is initiated by
A heat or UV light
B acid
C base
D catalyst only
Energy is required to break halogen–halogen bond homolytically.
The initiation step in free radical halogenation involves
A formation of alkyl radical
B formation of carbocation
C homolysis of halogen molecule
D termination of radicals
Halogen molecule splits into two radicals.
Which of the following is NOT a step in free radical substitution
A initiation
B propagation
C termination
D rearrangement
Rearrangement is typical of carbocations, not radicals.
In propagation step, the reaction mainly involves
A radical + radical
B radical + molecule
C ion + molecule
D ion + ion
Radical abstracts atom forming new radical.
Termination step occurs when
A radicals are generated
B radicals react with each other
C molecules react with molecules
D carbocations form
Radical concentration decreases, stopping chain reaction.
Chlorination of methane gives mixture of products because
A reaction is slow
B chlorine is selective
C successive substitution occurs
D carbocation rearrangement
H atoms can be replaced one by one.
Which halogenation reaction is most selective
A fluorination
B chlorination
C bromination
D iodination
Bromination is slow and highly selective.
Reactivity order of halogens in free radical substitution is
A I₂ > Br₂ > Cl₂ > F₂
B Br₂ > Cl₂ > F₂ > I₂
C F₂ > Cl₂ > Br₂ > I₂
D Cl₂ > Br₂ > F₂ > I₂
Reactivity decreases as bond dissociation energy increases.
Which halogenation is highly explosive
A iodination
B bromination
C chlorination
D fluorination
Fluorine reacts extremely violently.
Which halogenation requires UV light
A aromatic substitution
B alkene addition
C alkane substitution
D electrophilic substitution
UV light initiates free radical formation.
Relative reactivity of hydrogen atoms in alkane is
A 1° > 2° > 3°
B 3° > 2° > 1°
C 2° > 1° > 3°
D all equal
Stability of radical formed determines reactivity.
Free radical stability order is
A methyl > 1° > 2° > 3°
B 1° > 2° > 3°
C 3° > 2° > 1° > methyl
D all equal
More alkyl groups stabilise radical by hyperconjugation.
Major product of bromination of propane is
A 1-bromopropane
B 2-bromopropane
C equal mixture
D propyl bromide only
Bromination is selective; secondary radical formation favoured.
Major product of chlorination of propane is
A 1-chloropropane
B 2-chloropropane
C equal mixture
D propyl chloride only
Secondary hydrogen abstraction is favoured.
Free radical halogenation of alkanes is generally
A stereospecific
B regioselective
C non-selective
D stereoselective
Certain positions are favoured over others.
The selectivity of halogenation increases in the order
A F₂ < Cl₂ < Br₂ < I₂
B I₂ < Br₂ < Cl₂ < F₂
C Cl₂ < F₂ < Br₂ < I₂
D Br₂ < Cl₂ < F₂ < I₂
Less reactive halogen is more selective.
Iodination of alkanes is not feasible because
A reaction is too fast
B reaction is endothermic and reversible
C iodine radicals are unstable
D carbocations form
HI formed reverses the reaction.
Free radical substitution is favoured in
A dark conditions
B presence of peroxide only
C presence of light or heat
D aqueous medium
Energy source needed to generate radicals.
Addition of HBr to alkene in presence of peroxide proceeds via
A carbocation mechanism
B carbanion mechanism
C free radical mechanism
D concerted mechanism
Known as peroxide (Kharasch) effect.
The peroxide effect is observed only with
A HCl
B HBr
C HI
D HF
Only HBr has favourable energetics for radical chain.
Anti-Markovnikov addition is observed due to
A carbocation stability
B free radical stability
C nucleophilic attack
D electrophilic attack
More stable radical intermediate dictates orientation.
In peroxide effect, bromine atom attaches to carbon
A having more hydrogens
B having fewer hydrogens
C randomly
D attached to alkyl group
Radical formed is more stable.
The first step in peroxide effect involves
A homolysis of HBr
B homolysis of peroxide
C heterolysis of HBr
D carbocation formation
Peroxide generates alkoxy radicals.
Which intermediate is formed during peroxide effect
A carbocation
B carbanion
C free radical
D bromonium ion
Radical chain mechanism.
Why peroxide effect is not observed with HCl
A Cl radical is unstable
B propagation step is endothermic
C HCl bond is weak
D reaction is ionic
Chain reaction cannot sustain.
Free radical addition of HBr to propene gives mainly
A 1-bromopropane
B 2-bromopropane
C equal mixture
D allyl bromide
Anti-Markovnikov orientation.
Allylic bromination is carried out using
A Br₂
B NBS
C HBr
D NaBr
N-Bromosuccinimide selectively brominates allylic position.
Allylic radical is stabilised mainly by
A inductive effect
B hyperconjugation
C resonance
D steric effect
Radical is delocalised over π-system.
Benzylic radical is highly stable due to
A inductive effect
B resonance
C hyperconjugation only
D steric effect
Delocalisation over aromatic ring.
Which compound undergoes free radical substitution most readily
A methane
B ethane
C isobutane
D neopentane
Tertiary hydrogens are most reactive.
In free radical chain reaction, chain length means
A number of carbon atoms
B number of propagation steps per initiation
C number of radicals formed
D number of termination steps
Indicates efficiency of chain reaction.
Termination step reduces reaction rate because
A radicals are produced
B radicals are destroyed
C temperature decreases
D solvent changes
Fewer radicals means slower reaction.
Free radical reactions are generally favoured by
A low temperature
B high temperature
C acidic medium
D polar solvent
High temperature favours homolysis.
Which reaction proceeds by free radical mechanism
A hydration of alkene
B bromination of alkane
C nitration of benzene
D Friedel–Crafts
Classic free radical substitution.
Free radical substitution is NOT favoured in
A alkanes
B benzylic position
C aromatic ring
D allylic position
Aromatic ring prefers electrophilic substitution.
Free radical reactions are generally
A highly selective
B moderately selective
C non-selective
D completely random
Depends on stability of radicals.
Which factor increases rate of free radical reaction
A inhibitor
B radical scavenger
C light intensity
D oxygen
More radicals are generated.
Oxygen slows free radical reactions because it
A increases temperature
B acts as radical scavenger
C forms carbocations
D promotes termination
Oxygen traps radicals.
Free radical halogenation of alkanes is
A stereospecific
B stereoselective
C not stereospecific
D optically active
Planar radical intermediate leads to racemisation.
Which compound undergoes fastest bromination
A methane
B ethane
C propane
D isobutane
Contains tertiary hydrogens.
Which reaction gives anti-Markovnikov product
A HCl addition
B hydration
C HBr + peroxide
D ozonolysis
Radical pathway reverses orientation.
Free radical substitution reaction rate depends mainly on
A concentration of radicals
B solvent polarity
C nucleophile strength
D carbocation stability
More radicals → faster chain reaction.
Free radical mechanism involves which type of arrow
A curved arrow (double headed)
B straight arrow
C fishhook arrow
D dotted arrow
Single-headed arrow shows movement of one electron.
Which compound shows benzylic radical substitution easily
A benzene
B toluene
C nitrobenzene
D chlorobenzene
Benzylic hydrogen is easily abstracted.
Free radical substitution at benzylic position gives
A ring substitution
B side-chain substitution
C electrophilic substitution
D nucleophilic substitution
Radical forms at benzylic carbon.
Which condition suppresses free radical reactions
A UV light
B heat
C oxygen
D peroxide
Oxygen traps radicals.
Free radical halogenation of alkanes usually gives
A single product only
B rearranged product
C mixture of products
D optically pure product
Multiple H positions available.
Correct statement is
A Free radical reactions involve carbocations
B Free radical reactions require polar solvents
C Free radical reactions involve homolytic cleavage
D Free radical reactions always follow Markovnikov rule
Core principle of radical chemistry.