Chemistry
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How to determine the rate determining step (RDS) in a multistep organic chemical reaction?
When working through nucleophilic substitution (SN1 vs SN2) and elimination problems with multiple intermediates, I often get confused about which transition state barrier dictates the overall reaction rate law. What is the fundamental rule to identify the RDS?
Recommended Answer by Dr. Rashmi Sharma
Verified Educator
PhD in Chemistry (DU) • 14 yrs exp
The Rate Determining Step (RDS) is universally the elementary step with the highest Gibbs free energy of activation (ΔG‡) relative to its preceding reactant or intermediate.
1. Kinetic Bottleneck: The overall rate law is determined exclusively by the slow step. For SN1, carbocation formation is endothermic with a high activation barrier, making step 1 the RDS: Rate = k[R-X].
2. Catalyzed Pathways: Adding a catalyst lowers this specific highest barrier, shifting the equilibrium without altering thermodynamic yield.
1. Kinetic Bottleneck: The overall rate law is determined exclusively by the slow step. For SN1, carbocation formation is endothermic with a high activation barrier, making step 1 the RDS: Rate = k[R-X].
2. Catalyzed Pathways: Adding a catalyst lowers this specific highest barrier, shifting the equilibrium without altering thermodynamic yield.
Community Answers & Discussion (2)
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DRVerified Tutor • 46 mins agoThe Rate Determining Step (RDS) is universally the elementary step with the highest Gibbs free energy of activation (ΔG‡) relative to its preceding reactant or intermediate.
1. Kinetic Bottleneck: The overall rate law is determined exclusively by the slow step. For SN1, carbocation formation is endothermic with a high activation barrier, making step 1 the RDS: Rate = k[R-X].
2. Catalyzed Pathways: Adding a catalyst lowers this specific highest barrier, shifting the equilibrium without altering thermodynamic yield. -
KRStudent • 46 mins agoThank you ma'am! This cleared up my doubt regarding why polar protic solvents specifically accelerate step 1 by stabilizing the carbocation transition state.
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