Reactive Intermediates
In chemistry, reactive intermediates are termed as short-lived, highly reactive atoms with high energy. They rapidly transform into stable particles during a chemical reaction. In specific cases, by means of matrix isolation and at low-temperature reactive intermediates can be isolated.
Hydride Shift
A hydride shift is a rearrangement of a hydrogen atom in a carbocation that occurs to make the molecule more stable. In organic chemistry, rearrangement of the carbocation is very easily seen. This rearrangement can be because of the movement of a carbocation to attain stability in the compound. Such structural reorganization movement is called a shift within molecules. After the shifting of carbocation over the different carbon then they form structural isomers of the previous existing molecule.
Vinylic Carbocation
A carbocation where the positive charge is on the alkene carbon is known as the vinyl carbocation or vinyl cation. The empirical formula for vinyl cation is C2H3+. In the vinyl carbocation, the positive charge is on the carbon atom with the double bond therefore it is sp hybridized. It is known to be a part of various reactions, for example, electrophilic addition of alkynes and solvolysis as well. It plays the role of a reactive intermediate in these reactions.
Cycloheptatrienyl Cation
It is an aromatic carbocation having a general formula, [C7 H7]+. It is also known as the aromatic tropylium ion. Its name is derived from the molecule tropine, which is a seven membered carbon atom ring. Cycloheptatriene or tropylidene was first synthesized from tropine.
Stability of Vinyl Carbocation
Carbocations are positively charged carbon atoms. It is also known as a carbonium ion.
![**Transcription and Explanation for an Educational Website**
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**Title: Understanding the Reaction of Alcohols with Phosphorus Tribromide (PBr₃)**
**Question:**
What is the product of the following reaction?
**Reaction:**
The starting compound is a benzyl alcohol with the structure:
- A benzene ring attached to a CHOH group, which is further connected to a CH₂-CH₃ group.
**Reagent:**
\[ \text{PBr}_3 \]
**Possible Products:**
1. A benzene ring attached to a CHBr (with OH) group, connected to CH₂-CH₃.
2. A benzene ring attached to a CH-PBr₃ group, connected to CH₃.
3. A benzene ring attached to a CH-CH₃ group with PBr₃.
4. A benzene ring attached to a CHBr group, connected to CH₃.
5. A benzene ring attached to a CH₂ group, connected to CH₂-CH₃.
**Multiple Choice Options:**
- 1
- 2
- 3 (Correct Answer)
- 4
- 5
**Explanation:**
The reaction of alcohols with phosphorus tribromide (PBr₃) typically replaces the hydroxyl group (-OH) with a bromide (Br) atom. In this scenario, the hydroxyl group attached to the carbon next to the benzene ring (a primary alcohol) gets substituted with a bromide ion. This makes the correct product as option 4, where the compound changes from an alcohol to an alkyl bromide.
**Mechanism Insight:**
1. **Formation of the PBr₃ Intermediate:**
- The alcohol reacts with PBr₃, which helps in converting the OH group to a good leaving group, facilitating substitution by Br.
2. **Substitution Reaction:**
- The hydroxyl group is replaced by a bromide ion, resulting in the formation of the final bromoalkane product.
This reaction is a useful method for converting alcohols to alkyl halides, which can then undergo further chemical transformations.
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Note to students: Understanding this reaction not only helps in recognizing how functional groups can be manipulated but also provides insight into the application of these molecular changes in synthetic organic chemistry.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fd6d25517-f1db-4282-bf1e-57dce2991ffb%2F6916dd5a-c4ac-430a-9b36-2b278e48fea5%2Fbxw5r38_processed.jpeg&w=3840&q=75)
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