Basics in Organic Reactions Mechanisms
In organic chemistry, the mechanism of an organic reaction is defined as a complete step-by-step explanation of how a reaction of organic compounds happens. A completely detailed mechanism would relate the first structure of the reactants with the last structure of the products and would represent changes in structure and energy all through the reaction step.
Heterolytic Bond Breaking
Heterolytic bond breaking is also known as heterolysis or heterolytic fission or ionic fission. It is defined as breaking of a covalent bond between two different atoms in which one atom gains both of the shared pair of electrons. The atom that gains both electrons is more electronegative than the other atom in covalent bond. The energy needed for heterolytic fission is called as heterolytic bond dissociation energy.
Polar Aprotic Solvent
Solvents that are chemically polar in nature and are not capable of hydrogen bonding (implying that a hydrogen atom directly linked with an electronegative atom is not found) are referred to as polar aprotic solvents. Some commonly used polar aprotic solvents are acetone, DMF, acetonitrile, DMSO, etc.
Oxygen Nucleophiles
Oxygen being an electron rich species with a lone pair electron, can act as a good nucleophile. Typically, oxygen nucleophiles can be found in these compounds- water, hydroxides and alcohols.
Carbon Nucleophiles
We are aware that carbon belongs to group IV and hence does not possess any lone pair of electrons. Implying that neutral carbon is not a nucleophile then how is carbon going to be nucleophilic? The answer to this is that when a carbon atom is attached to a metal (can be seen in the case of organometallic compounds), the metal atom develops a partial positive charge and carbon develops a partial negative charge, hence making carbon nucleophilic.
![**Determining If the Reaction is a Nucleophilic Substitution Reaction**
**Reaction Given:**
The image illustrates a chemical reaction and prompts whether it's an example of a nucleophilic substitution reaction. The reaction provided is as follows:
\[ \text{Molecule A (benzene with one hydrogen attached)} + \text{Molecule B (NO}_2^+) \rightarrow \text{Product (benzene with a NO}_2 \text{ group attached)} + \text{H}^+ \]
**Detailed Description:**
1. **Reactants:**
- **Molecule A:** This is a benzene ring with one hydrogen atom attached to it.
- **Molecule B:** This is a positively charged nitro group (\( \text{NO}_2^+ \)).
2. **Products:**
- The product is a benzene ring with a NO\(_2\) group attached to it, which replaces the hydrogen atom initially attached to the benzene ring.
- A proton (H\(^+\)) is also released as a byproduct.
**Analysis:**
In this reaction, the benzene ring (Molecule A) undergoes an electrophilic substitution reaction where the hydrogen atom is replaced by a nitro group (NO\(_2\)). Here, the nitro group is an electrophile (electron-seeking species), which attacks the electron-rich benzene ring.
The presence of the \( \text{NO}_2^+ \) ion as the substituent indicates that this is an electrophilic substitution reaction rather than a nucleophilic substitution reaction.
**Conclusion:**
Therefore, the reaction depicted is an example of an electrophilic substitution reaction, not a nucleophilic substitution reaction.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Ff1d2ed3e-5db6-4b34-adcc-843852a358f0%2F9a0da629-67db-42fd-8037-06329438bfef%2Fr4jfmwl_processed.jpeg&w=3840&q=75)
![### Nucleophilic Substitution Reaction
**Is this a nucleophilic substitution reaction?**
- [ ] Yes
- [ ] No
**If this is a nucleophilic substitution reaction, answer the remaining questions in this table.**
1. **What word or two-word phrase is used to describe the role Molecule A plays in this reaction?**
- [__________]
2. **What word or two-word phrase is used to describe the role Molecule B plays in this reaction?**
- [__________]
3. **Use a δ⁺ symbol to label the electrophilic carbon that is attacked during the substitution.**
4. **Highlight the leaving group on the appropriate reactant.**](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Ff1d2ed3e-5db6-4b34-adcc-843852a358f0%2F9a0da629-67db-42fd-8037-06329438bfef%2Fi2ydb5c_processed.jpeg&w=3840&q=75)
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