Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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Explain why only the meso form of 1,2-dibromo-1,2-diphenylethane is formed.
Transcribed Image Text:### Meso Compound
- **Definition**: A molecule that has two or more stereogenic centers but also has a plane of symmetry.
- **Optical Activity**: Optically Inactive
### Diagram Explanation
The diagram illustrates the structural transformation of a compound showing its stereochemistry.
1. **Top Left**: The initial molecule is depicted with two benzene rings and a bromine (Br) atom at a chiral center, represented with wedges and dashes to indicate three-dimensional orientation.
2. **Next Steps**: The arrows indicate the movement of electrons or chemical transformations between the structures.
- The dotted line in the structure shows the rotation or flipping of molecular parts.
3. **Middle Structures**: Shows step-by-step changes in orientation of the substituents around the central carbon, illustrating how the structure's symmetry is achieved.
4. **Final Structure**: The last image on the bottom right shows the molecule with an orange line, indicating a plane of symmetry, causing the compound to be optically inactive despite having stereogenic centers.
This diagram emphasizes understanding the three-dimensional nature of molecules and identifying symmetry to classify meso compounds correctly.
![### Free Radical Bromination of Bibenzyl
#### Overall Reaction
The free radical bromination of bibenzyl involves the addition of bromine to produce 1,2-dibromo-1,2-diphenylethane under ultraviolet (UV) light:
\[ \text{bibenzyl} + 2\text{Br}_2 \overset{\text{uv light}}{\longrightarrow} \text{1,2-dibromo-1,2-diphenylethane} + 2\text{HBr} \]
#### Mechanism
1. **Initiation Step:**
- **Light-induced Homolytic Cleavage:**
- \( \text{Br}_2 \rightarrow 2\text{Br} \cdot \)
- The reaction begins with the homolytic cleavage of the bromine molecule under UV light, producing two bromine radicals (\( \text{Br} \cdot \)).
2. **Propagation Steps:**
- **Step 1:**
- A bromine radical abstracts a hydrogen atom from the bibenzyl, forming HBr and a new radical on the bibenzyl:
- \( \text{Br} \cdot + \text{bibenzyl} \rightarrow \text{HBr} + \cdot \text{bibenzyl-radical} \)
- **Step 2:**
- The newly formed bibenzyl radical reacts with another bromine molecule to form 1,2-dibromo-1,2-diphenylethane and another bromine radical:
- \( \cdot \text{bibenzyl-radical} + \text{Br}_2 \rightarrow \text{1,2-dibromo-1,2-diphenylethane} + \text{Br} \cdot \)
3. **Termination Step:**
- The reaction terminates when two bromine radicals combine to form a bromine molecule:
- \( \text{Br} \cdot + \text{Br} \cdot \rightarrow \text{Br}_2 \)
This sequence effectively illustrates the free radical chain reaction mechanism, consisting of initiation, propagation, and termination steps, in the bromination process.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fd2844fe3-43c8-4d71-aeb3-c2d3e96eb4f2%2F0f9e311a-898a-4b72-93e4-c4693ea42995%2Fqqlki6w_processed.jpeg&w=3840&q=75)
Transcribed Image Text:### Free Radical Bromination of Bibenzyl
#### Overall Reaction
The free radical bromination of bibenzyl involves the addition of bromine to produce 1,2-dibromo-1,2-diphenylethane under ultraviolet (UV) light:
\[ \text{bibenzyl} + 2\text{Br}_2 \overset{\text{uv light}}{\longrightarrow} \text{1,2-dibromo-1,2-diphenylethane} + 2\text{HBr} \]
#### Mechanism
1. **Initiation Step:**
- **Light-induced Homolytic Cleavage:**
- \( \text{Br}_2 \rightarrow 2\text{Br} \cdot \)
- The reaction begins with the homolytic cleavage of the bromine molecule under UV light, producing two bromine radicals (\( \text{Br} \cdot \)).
2. **Propagation Steps:**
- **Step 1:**
- A bromine radical abstracts a hydrogen atom from the bibenzyl, forming HBr and a new radical on the bibenzyl:
- \( \text{Br} \cdot + \text{bibenzyl} \rightarrow \text{HBr} + \cdot \text{bibenzyl-radical} \)
- **Step 2:**
- The newly formed bibenzyl radical reacts with another bromine molecule to form 1,2-dibromo-1,2-diphenylethane and another bromine radical:
- \( \cdot \text{bibenzyl-radical} + \text{Br}_2 \rightarrow \text{1,2-dibromo-1,2-diphenylethane} + \text{Br} \cdot \)
3. **Termination Step:**
- The reaction terminates when two bromine radicals combine to form a bromine molecule:
- \( \text{Br} \cdot + \text{Br} \cdot \rightarrow \text{Br}_2 \)
This sequence effectively illustrates the free radical chain reaction mechanism, consisting of initiation, propagation, and termination steps, in the bromination process.
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