Textbook Question
For each set of reactive intermediates, rank them in order of reactivity (1 = most reactive).
(c)
6. Thermodynamics and Kinetics
Carbocation Stability
0:59 minutesProblem 3b
Textbook Question
Which of the carbocations in part a is most stable?
1. the isobutyl cation?
2. the n-butyl cation?
3. the sec-butyl cation?
Verified step by step guidance1
Step 1: Understand the concept of carbocation stability. Carbocation stability is influenced by factors such as the number of alkyl groups attached to the positively charged carbon (hyperconjugation) and the inductive effect. Tertiary carbocations are generally more stable than secondary, which are more stable than primary carbocations.
Step 2: Analyze the structure of the isobutyl cation. The isobutyl cation has a primary carbocation, meaning the positively charged carbon is attached to only one alkyl group. This makes it less stable compared to secondary or tertiary carbocations.
Step 3: Analyze the structure of the n-butyl cation. The n-butyl cation also has a primary carbocation, with the positively charged carbon attached to one alkyl group. Its stability is similar to the isobutyl cation.
Step 4: Analyze the structure of the sec-butyl cation. The sec-butyl cation has a secondary carbocation, where the positively charged carbon is attached to two alkyl groups. This increases its stability due to hyperconjugation and inductive effects.
Step 5: Compare the stability of the three carbocations. Based on the analysis, the sec-butyl cation is the most stable because it is a secondary carbocation, while the isobutyl and n-butyl cations are primary carbocations and therefore less stable.
Verified video answer for a similar problem:This video solution was recommended by our tutors as helpful for the problem above
Video duration:
59sKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Carbocation Stability
Carbocation stability is influenced by the degree of substitution on the positively charged carbon atom. Tertiary carbocations, which have three alkyl groups attached, are more stable than secondary and primary carbocations due to hyperconjugation and inductive effects. The more alkyl groups surrounding the carbocation, the greater the electron-donating effect, which helps to stabilize the positive charge.
Recommended video:
Guided course
05:58
Determining Carbocation Stability
Hyperconjugation
Hyperconjugation is a stabilizing interaction that occurs when the electrons in a sigma bond (usually C-H or C-C) interact with an adjacent empty p-orbital of a carbocation. This delocalization of electrons helps to spread out the positive charge, thereby increasing the stability of the carbocation. The more hyperconjugative interactions available, the more stable the carbocation becomes.
Recommended video:
Guided course
04:28Understanding trends of alkene stability.
Inductive Effect
The inductive effect refers to the electron-withdrawing or electron-donating effects transmitted through sigma bonds in a molecule. Alkyl groups are electron-donating, which can help stabilize a carbocation by reducing the positive charge through the inductive effect. The presence of more alkyl groups around a carbocation enhances its stability due to this electron-donating property.
Recommended video:
Guided course
01:47Understanding the Inductive Effect.
Related Videos
Related Practice