Reaction intermediates are species which
A exist before reaction starts
B are more stable than products
C are formed during reaction and consumed later
D can be isolated easily
Intermediates appear in the reaction pathway but do not appear in the overall equation.
Which of the following is NOT a reaction intermediate
A Carbocation
B Free radical
C Transition state
D Carbanion
Transition state is not a discrete species; it cannot be isolated.
A carbocation is best described as
A negatively charged carbon
B neutral carbon with odd electron
C positively charged carbon
D carbon with lone pair
Carbocation has a sextet of electrons and positive charge.
Hybridisation of carbocation carbon is generally
A sp
B sp²
C sp³
D dsp²
Carbocation is trigonal planar with an empty p-orbital.
Stability order of carbocations is
A 1° > 2° > 3°
B 2° > 1° > 3°
C 3° > 2° > 1°
D 1° > 3° > 2°
More alkyl groups provide hyperconjugation and +I effect.
Carbocation stability increases due to
A −I effect
B hyperconjugation
C steric hindrance
D electron withdrawal
Electron donation stabilizes the electron-deficient carbon.
A benzylic carbocation is highly stable due to
A inductive effect
B hyperconjugation only
C resonance
D steric effect
Positive charge is delocalized over the benzene ring.
A free radical contains
A positive charge
B negative charge
C unpaired electron
D paired electrons only
Free radicals are neutral species with one unpaired electron.
Hybridisation of free radical carbon is
A sp
B sp²
C sp³
D variable
Free radical carbon is planar with one unpaired electron in p-orbital.
Stability order of free radicals is
A CH₃• > 1° > 2° > 3°
B 1° > 2° > 3°
C 3° > 2° > 1°
D all equal
Same factors as carbocations: hyperconjugation and +I effect.
A carbanion is
A electron-deficient
B neutral species
C electron-rich species
D transition state
Carbanions have a negative charge and a lone pair.
Hybridisation of carbanion carbon is generally
A sp
B sp²
C sp³
D dsp²
Carbanions are pyramidal due to lone pair repulsion.
Stability order of carbanions is
A 3° > 2° > 1°
B 2° > 3° > 1°
C 1° > 2° > 3°
D all equal
Alkyl groups destabilize negative charge due to +I effect.
Electron withdrawing groups increase stability of
A carbocations
B free radicals
C carbanions
D alkenes
−I effect stabilizes negative charge.
Transition state differs from intermediate because it
A has finite lifetime
B can be isolated
C is highest energy point
D exists between two steps
Transition state corresponds to the peak of energy barrier.
Transition state is represented as
A [ ]
B ( )
C ‡
D →
Double dagger symbol represents transition state.
The energy profile diagram plots
A energy vs time
B energy vs concentration
C energy vs reaction coordinate
D energy vs temperature
Reaction coordinate represents progress of reaction.
Activation energy is the energy difference between
A reactants and products
B reactants and transition state
C products and intermediates
D intermediates and products
Minimum energy required to cross the energy barrier.
Lower activation energy results in
A slower reaction
B no reaction
C faster reaction
D equilibrium shift
More molecules can cross the barrier per unit time.
Catalyst increases reaction rate by
A increasing ΔH
B lowering activation energy
C increasing product stability
D changing equilibrium constant
Catalyst provides alternate lower-energy pathway.
In an exothermic reaction
A products have higher energy than reactants
B reactants have higher energy than products
C ΔH is positive
D activation energy is zero
Energy is released during reaction.
In an endothermic reaction
A ΔH is negative
B products are lower in energy
C products are higher in energy
D activation energy is negative
Energy is absorbed during reaction.
Which has higher activation energy
A catalysed reaction
B uncatalysed reaction
C both equal
D spontaneous reaction
Catalyst lowers activation energy.
Number of transition states in a reaction equals
A number of intermediates
B number of steps
C number of products
D number of reactants
Each step has one transition state.
Number of intermediates in a reaction equals
A number of steps
B number of steps − 1
C number of transition states
D always zero
Intermediates lie between steps.
Rate-determining step corresponds to
A lowest energy step
B highest energy barrier
C fastest step
D equilibrium step
Slowest step controls overall rate.
Rate-determining step has
A lowest Ea
B highest Ea
C zero Ea
D negative Ea
Highest activation energy → slowest step.
Kinetically controlled product formation depends on
A product stability
B temperature only
C activation energy
D equilibrium constant
Lower Ea product forms faster.
Thermodynamically controlled product depends on
A rate of formation
B activation energy only
C product stability
D catalyst
More stable product predominates at equilibrium.
Kinetic control is favoured at
A high temperature
B low temperature
C equilibrium conditions
D presence of catalyst
Reaction is irreversible and fast; equilibrium not reached.
Thermodynamic control is favoured at
A low temperature
B very short time
C high temperature
D absence of equilibrium
Reversibility allows equilibrium to establish.
Under kinetic control, major product is
A most stable
B formed fastest
C formed in equilibrium
D least substituted
Product with lower Ea dominates.
Under thermodynamic control, major product is
A least stable
B formed fastest
C most stable
D least substituted
Equilibrium favours lower energy product.
Carbocation rearrangement occurs to
A decrease reaction rate
B increase activation energy
C form more stable carbocation
D stop reaction
Hydride or alkyl shift increases stability.
Hydride shift involves movement of
A H⁺
B H•
C H⁻
D H₂
A hydride ion migrates with electron pair.
Alkyl shift involves movement of
A CH₃⁺
B CH₃•
C CH₃⁻
D alkyl group with bonding electrons
Entire group migrates with its electron pair.
Rearrangement is NOT observed in
A SN1 reactions
B carbocation reactions
C SN2 reactions
D dehydration of alcohols
SN2 has no carbocation intermediate.
Free radical rearrangements are
A very common
B impossible
C less common than carbocations
D more common than carbocations
Radical rearrangements occur but are rarer.
Energy difference between reactants and products is
A activation energy
B free energy of reaction
C resonance energy
D collision energy
Represents thermodynamic feasibility.
Which species cannot be detected even indirectly
A carbocation
B free radical
C carbanion
D transition state
Lifetime is extremely short.
Reaction intermediate lies
A at energy minimum
B at energy maximum
C above transition state
D below products only
Intermediates correspond to valleys in energy profile.
More stable intermediate means
A faster reaction always
B higher activation energy of next step
C lower activation energy of next step
D reaction stops
Very stable intermediates slow further conversion.
SN1 reaction proceeds through
A free radical
B carbanion
C carbocation
D concerted mechanism
Ionization step forms carbocation.
SN2 reaction has
A two steps
B carbocation intermediate
C single step
D rearrangement
Concerted mechanism, no intermediate.
Which reaction has only one transition state
A SN1
B E1
C SN2
D E1cb
Single-step mechanism.
Energy profile of SN1 reaction shows
A one peak
B two peaks
C three peaks
D no peak
Two-step mechanism → two transition states.
The highest peak in energy profile corresponds to
A intermediate
B product
C transition state of RDS
D reactant
Rate-determining step has highest Ea.
In exothermic reaction, activation energy of forward reaction is
A greater than reverse
B less than reverse
C equal to reverse
D zero
Products are lower in energy.
Reaction with low activation energy but unstable product is
A thermodynamic
B kinetic
C equilibrium
D resonance-controlled
Fast formation but unstable product.
Correct statement is
A Intermediate is highest energy species
B Transition state can be isolated
C Catalyst lowers Ea but not ΔG
D Rearrangements occur in SN2
Catalyst affects kinetics, not thermodynamics.