Q7-70E - Organic Chemistry (Mcmurry)

Question

Sketch the transition-state structures involved in the reaction of HBr with 1-pentene (Problem 7-69). Tell whether each structure resembles reactant or product.

Step-by-Step Solution

Answer

The transition-state structures involved in the reaction between HBr and 1-pentene are,

Step 1: Transition-state structures

Transition-state structures are unstable structures where all chemical transformations take place. Its lifetime is very short and can be considered a short-lived intermediate. 

 

Step 2: The transition-state structures involved in the reaction of HBr with 1-pentene

For both the reaction paths, the first step, the carbocation formation, is endergonic, and both the transition states have a quite resemblance to carbocation intermediates. The carbocation intermediate is the same for the exergonic second step. The number 1 transition state is for 1-bromopentane and is more like the carbocation intermediate than the number 1 transition state for 2-bromopentane.

Transition states for 1-bromopentane and 2-bromopentane path