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.
![### Cycloaddition Reaction of Phellandrene Isomers
#### Problem Statement
Only ONE of the α- or β-phellandrene isomers will react with the depicted alkyne-containing dienophile via a thermal [4 + 2] cycloaddition reaction; the other isomer will not react. Draw the reactive phellandrene isomer in the left box, and draw the cycloaddition product (defining all stereocenters) in the right box.
#### Instructions
1. **Reactant and Reaction Conditions**:
- The dienophile is depicted with the structure COOH and COOH on either side of a triple bond.
- The reaction requires heat to proceed.
- The reaction type is a [4 + 2] cycloaddition.
2. **Tasks**:
- Identify the correct phellandrene isomer (either α- or β-phellandrene) that will react with the dienophile.
- Draw this reactive phellandrene isomer in the left box.
- Draw the resulting cycloadduct product in the right box. Be sure to clearly define all stereocenters in the resulting compound.
3. **Diagram Explanation**:
- **Initial State (Left Box)**: Leave this space for drawing the chosen phellandrene isomer.
- **Reaction Scheme (Middle Section)**: It shows the alkyne-containing dienophile reacting with heat to undergo a [4 + 2] cycloaddition.
- **Final Product (Right Box)**: Leave this space for drawing the final product of the cycloaddition reaction, clearly stating the stereocenters.
#### Additional Notes:
- Ensure understanding of the structural differences between α- and β-phellandrene.
- Understand the [4 + 2] cycloaddition mechanism to predict the product and its stereochemistry accurately.
- Remember to label all stereocenters in the product to clarify the 3-dimensional structure of the molecule.
By following these steps, a clear and concise representation of the reaction and its products should be obtained, providing an educational understanding of the cycloaddition process involving phellandrene isomers.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Feb2e2013-15d0-4e81-b731-8816ed407a57%2Ff14f8fa4-0c23-4416-9e42-706a7577e9c0%2F1vo2vtq_processed.png&w=3840&q=75)
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