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After completing this section, you should be able to. describe the geometry of a given carbocation. arrange a given series of carbocations in order of increasing or decreasing stability. explain the relative stability of methyl, primary, secondary and tertiary carbocations in terms of hyperconjugation and inductive effects.
- Markovnikov's Rule
After completing this section, you should be able to. use...
- The Hammond Postulate
The reaction takes place through a two step mechanism which...
- Hyperconjugation
The structure of the ethyl carbocation, according to the...
- Markovnikov's Rule
Jan 23, 2023 · Carbocation rearrangements are extremely common in organic chemistry reactions are are defined as the movement of a carbocation from an unstable state to a more stable state through the use of various structural reorganizational "shifts" within the molecule. Once the carbocation has shifted over to a different carbon, we can say that there is a ...
Typically over 90% of molecules will rearrange before they react with a nucleophile. Once you’ve checked your carbocation for any rearrangements, did those rearrangements, and your carbocation as stable as it can be given the molecular structure of your compound, then you can proceed your reaction.
- What Is A carbocation?
- Formation of Carbocations
- Factors That Stabilize Carbocations – Substitution
- Factors That Stabilize Carbocations – Resonance
- The Importance of Carbocation Stability in Reactions
- Factors That Stabilize Carbocations – Adjacent Lone Pairs
- Which Factor Is More Important – Substitution Or Resonance?
- Some Factors That Destabilize Carbocations
- Some Special Cases
- Summary
A positively charged carbon atom bearing three covalent bonds and an empty orbital is called a carbocation (or more officially, a “carbenium” ion, although for our purposes we’re going to use “carbocation” [Note 1]) Other than the charge of +1 on the central carbon, the structure and properties of the vast majority [Note 2] of carbocations closely ...
Carbocations are important intermediates in many reactions.(An intermediate, as opposed to a transition state, is a potentially isolable species in a reaction and occupies a potential energy minimum in a reaction coordinate diagram. Transition states have partial bonds, extremely short lifetimes and cannot be isolated). Lacking a full octet of elec...
The experimentally measured stability [Note 4] of carbocations shows the following trend: Methyl (least stable) < primary < secondary < tertiary (most stable) In other words, carbocation stability increases as C-H bonds are replaced with C-C bonds. Why? Being electron-poor, carbocations are stabilized through donation of electron density from neigh...
A good working principle in organic chemistry is that concentrated charge is generally more unstable (higher-energy) than dilute charge (lower-energy) [Note 5] One place we’ve seen this before is in the concept of polarizability, where a big anion like iodide I(-) is more stable than a small ion like F(-) because the negative charge is spread out o...
Let’s return to the role of carbocations as intermediates in several key organic reactions. The rate-determining step of the reaction below is protonation of the pi bond with H+ to give a carbocation intermediate. Which of the two reactions do you think is faster? If you answered correctly, congratulations! You’ve shown you understand the reason be...
There’s another factor that stabilizes carbocations that we haven’t touched on yet. If a carbocation is formed adjacent to an atom bearing a lone pair (i.e. a Lewis base) then that atom can donate its pair of electrons to the carbocation, forming a new pi-bond in the process. This is known as “pi-donation” (See article – Pi Donation) It might seem ...
So we have two factors that influence carbocation stability: substitution (primary, secondary, tertiary) and resonance. So which is more important? “they’re bothimportant” is my non-answer to this question. The actual way to answer this question is to look at experimental results. One way to measure carbocation stability is to take a related series...
Since electron-donating groups help to stabilize carbocations, it would make sense to expect that electron-withdrawing groups will destabilize carbocations. As we touched on above, electronegative atoms with lone pairs like O, N, and F that are directly attached to a carbocation will actually help to stabilizecarbocations through pi-donation. I wou...
For the sake of completeness we should probably mention one last factor that is more of a second-semester topic but has a very large impact on the stability of certain carbocations. Some molecules have a particularly stable property known as aromaticity. (See article –Rules For Aromaticity) A related phenomenon called antiaromaticity is responsible...
Carbocations are positively charged, six-electron carbon atoms with an empty p-orbital. They are important intermediates in many reactions and are highly reactive towards Lewis bases. Three key factors stabilize carbocations: 1. First, they are stabilized by adjacent alkyl groups, which can donate electron density to the electron-deficient carbon a...
Whenever reactants like alkyl halides form carbocations, the carbocations are subject to a phenomenon known as carbocation rearrangement. A carbocation is highly reactive and holds the positive charge on carbon with a sextet rather than an octet. There are two types of rearrangements: hydride shift and alkyl shift.
Dec 1, 2021 · Carbocations! Alcohol A gives a reasonably stable, 3° carbocation, which reacts with the electron-rich benzene ring in a Friedel–Crafts alkylation to give the product. However, alcohol B gives a less stable, 2° carbocation – at least initially! Now, if you look at one of the carbon atoms next-door – a hydrogen can migrate with its pair ...
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Carbocation rearrangements | Organic Chemistry 1: An open textbook. 8.4. Carbocation rearrangements. Carbocation rearrangements are common in organic chemistry and are defined as the movement of a carbocation from an unstable state to a more stable state through the use of various structural reorganizational “shifts” within the molecule.
