Organic Chemistry 1 · Reasoning about reactions
Reaction energy and kinetics: practice problems
42 problems, each with its worked solution. Open one to read every step, or filter by tag.
Start drawing: Reaction energy and kinetics
Tap one to draw it yourself with every arrow checked, or watch the steps. No sign-up.
- Locate the rate-determining step of an SN1 reaction
- tert-Butyl alcohol from 2-methylpropene: a hydration profile
- 2-Methylpropene from tert-butyl bromide: an E1 profile
- Ethene from bromoethane: a one-step E2 profile
- HBr + 1,3-butadiene at −80 °C: kinetic 1,2-addition profile
- HBr + 1,3-butadiene at 40 °C: thermodynamic 1,4 profile
- 2-Bromopropane from propene: a two-step profile
- tert-Butyl chloride from 2-methylpropene: a two-step profile
- HCl + 3-methyl-1-butene: hydride-shift energy profile
Draw the mechanism 12
- Locate the rate-determining step of an SN1 reactionMap each elementary step of an SN1 solvolysis onto its energy profile and apply the Hammond postulate to the ionization transition state.
- tert-Butyl alcohol from 2-methylpropene: a hydration profileDraw the three steps of acid-catalysed hydration of 2-methylpropene and map them onto a profile with two intermediates and a rate-determining protonation.
- 2-Methylpropene from tert-butyl bromide: an E1 profileDraw the two E1 steps of tert-butyl bromide in hot ethanol and place the slow ionization and the fast deprotonation on an energy diagram.
- Ethene from bromoethane: a one-step E2 profileDraw the single concerted E2 step that turns bromoethane into ethene and connect it to an energy diagram with one transition state and no intermediate.
- HBr + 1,3-butadiene at −80 °C: kinetic 1,2-addition profileDraw HBr addition to 1,3-butadiene at −80 °C and explain from the energy profile why the 1,2-adduct, 3-bromo-1-butene, is the kinetic product.
- HBr + 1,3-butadiene at 40 °C: thermodynamic 1,4 profileDraw HBr addition to 1,3-butadiene at 40 °C through the allylic cation and explain from the energy profile why (E)-1-bromo-2-butene is the thermodynamic product.
- 2-Bromopropane from propene: a two-step profileDraw the two steps of HBr addition to propene and use the Hammond postulate to explain why the secondary cation, and so 2-bromopropane, forms.
- tert-Butyl chloride from 2-methylpropene: a two-step profileDraw the two steps of HCl addition to 2-methylpropene and use the Hammond postulate to explain why the tertiary cation forms and controls the rate.
- HCl + 3-methyl-1-butene: hydride-shift energy profileDraw HCl addition to 3-methyl-1-butene with its 1,2-hydride shift and explain the profile with two carbocation valleys leading to 2-chloro-2-methylbutane.
- SN1 methanolysis of 2-bromo-2-methylbutane: energy profileDraw the three SN1 steps of 2-bromo-2-methylbutane in methanol and identify the rate-determining ionization and the two intermediates on the profile.
- tert-Butyl alcohol from tert-butyl chloride: a three-step profileDraw the three SN1 steps for tert-butyl chloride in water and map them onto an energy diagram with three transition states, two intermediates and a rate-determining ionization.
- Pentanenitrile from 1-bromobutane: a one-step SN2 profileDraw the single concerted SN2 step of cyanide with 1-bromobutane and explain why its energy diagram has one transition state and no intermediate.
Predict the product 4
- Predict a heating effect on KUse reaction enthalpy to reason about equilibrium temperature dependence.
- Which reaction has a positive ΔS°?Predict the sign of ΔS° by counting the molecules formed and consumed in a reaction.
- What does the transition state resemble?Apply the Hammond postulate to predict the structure of a transition state.
- SN1 rate when the nucleophile concentration doublesPredict how an SN1 rate responds to nucleophile concentration from the position of the rate-determining step.
Classify 2
- Count states on a two-step profileDistinguish a cationic intermediate from a transition state.
- Which step limits the rate?Identify the rate-determining step of a multistep reaction.
Compare 3
- Compare catalyzed equilibrium mixturesSeparate catalytic acceleration from a change in equilibrium composition.
- Kinetic versus thermodynamic controlPredict which product dominates under kinetic or thermodynamic control.
- Rank three steps from fastest to slowest by ΔG‡Order elementary steps by rate from their free energies of activation.
Calculate 10
- Convert standard free energy into KApply the sign and logarithm in the thermodynamic equilibrium relation.
- Compare competing activation routesCalculate a product-formation rate ratio from supplied barriers.
- Activation energy from rate constants at two temperaturesCalculate an activation energy from rate constants measured at two temperatures with the two-point Arrhenius equation.
- Rate increase for a 10 K riseUse the Arrhenius equation to calculate how a rate constant changes with temperature.
- ΔH of methane chlorination from bond energiesEstimate a reaction enthalpy from bond dissociation energies.
- ΔG° from ΔH° and ΔS° at 298 KCalculate a standard free-energy change from ΔH°, ΔS° and temperature, converting entropy to kJ.
- ΔG° from an equilibrium constantCalculate a standard free-energy change from an equilibrium constant.
- Temperature at which an endothermic reaction turns favorableCalculate the temperature at which ΔG° changes sign for a reaction with positive ΔH° and ΔS°.
- Rate ratio from a barrier differenceRelate a difference in activation free energy to a ratio of rate constants.
- SN2 rate when both concentrations doubleUse a second-order SN2 rate law to predict the rate change when both reactant concentrations change.
Find the error 2
- Diagnose a rate claimIdentify missing kinetic information in a thermodynamic argument.
- Diagnose: "endothermic reactions are never favorable"Diagnose a misconception that a positive ΔH° alone rules out a favorable equilibrium.
Interpret the evidence 3
- Find a reverse activation barrierUse a common energy reference for forward and reverse barriers.
- Isotope effect evidence: E2 versus E1Interpret a primary deuterium isotope effect to decide whether C–H cleavage is in the rate-determining step of an elimination.
- Reading a two-step energy diagramDistinguish intermediates from transition states on a reaction energy diagram.
Work backward 1
- Recover an intermediate energyReconstruct a local minimum from barriers referenced in opposite directions.
Plan a synthesis 2
- Choose a discriminating initial-rate experimentDesign a controlled concentration change to test kinetic participation.
- Choose conditions for the 1,4-adduct of butadiene + HBrPlan reaction conditions that give the thermodynamic product of a conjugated diene addition.
Explain why 3
- Explain a catalyst in both directionsApply microscopic reversibility to a specified elementary reversible pair.
- Why radical bromination is more selective than chlorinationExplain halogenation selectivity with the Hammond postulate and the energetics of hydrogen abstraction.
- Microscopic reversibility: hydration vs dehydrationApply microscopic reversibility to predict the intermediates and transition states of a reverse reaction.
Stuck on your own homework?
Snap it — first scan free, no sign-up
Scanning every week? Scan Standard: for about problems