Match the correct reaction mechanism (El or Sn1) with each reaction scheme. O Hold and drag to reorder 1. = E1 2. = E1 3. = SN1 4. = SN1 = E1 = SN1 OH H2SO, 2) H20 Br 3) MEOH он 4) H,PO,
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.
- Reagent: H₂SO₄
- This reaction typically indicates an E1 mechanism where the alcohol is converted into an alkene via elimination.
2. 
- Reagent: H₂O
- Usually, a secondary halide in the presence of water undergoes an SN1 mechanism involving carbocation formation followed by nucleophilic attack.
3. 
- Reagent: MeOH
- A tertiary bromide with methanol often proceeds via an SN1 mechanism, involving carbocation formation and nucleophilic substitution.
4. 
- Reagent: H₃PO₄
- This reaction’s context suggests an E1 mechanism where the alcohol undergoes dehydration to form an alkene.
Let's consider these examples in detail:
### Detailed Reaction Analysis
**1. OH Group with H₂SO₄:**
- Mechanism: E1
- The OH group is protonated by H₂SO₄, resulting in the formation of a water molecule, which is a good leaving group. This is followed by the formation of a carbocation intermediate and finally, elimination to form an alkene.
**2. Cl Group with H₂O:**
- Mechanism: SN1
- The chloride ion leaves, forming a carbocation. After the carbocation is formed, water acts as the nucleophile, attacking the positively charged carbon, resulting in substitution.
**3. Br Group with MeOH:**
- Mechanism: SN1
- The bromide ion leaves, again forming a carbocation. Methanol then acts as the nucleophile](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F7cf86841-3385-4013-879d-ba0a640897cd%2F2e952f49-7e05-4314-a6e8-122cf441972f%2F8d7ds1_processed.jpeg&w=3840&q=75)
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