Consider the given reaction
`CH_(3)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)C-CH_(2)-OH overset("conc." H_(2)SO_(4))underset(Delta)to "Alkene(major)"`
Identify alkene.

Options

A. `CH_(3)-CH_(2)-CH=CH_(2)`
B. `CH_(3)-CH=CH-CH_(3)`
C. `(CH_(3))_(2)C=C(CH_(3))_(2)`
D. `CH_(3)-CH=underset(CH_(3))underset(|)C-CH_(3)`

Answer

To identify the alkene formed from the given reaction, we will follow these steps:

### Step 1: Identify the starting compound
The starting compound is 2-methyl-2-butanol, represented as:
\[ \text{CH}_3 - \text{C(OH)(CH}_3) - \text{C(CH}_3) - \text{CH}_2 - \text{OH} \]

### Step 2: Understand the role of concentrated H2SO4
Concentrated sulfuric acid (H2SO4) acts as a dehydrating agent, which means it will remove a water molecule (H2O) from the alcohol to form an alkene.

### Step 3: Remove the hydroxyl group (OH)
The hydroxyl group (OH) will be protonated by the concentrated H2SO4, making it a better leaving group. As a result, water (H2O) will be eliminated, leading to the formation of a carbocation.

### Step 4: Formation of carbocation
When the OH group is removed, a carbocation is formed. In this case, we can have a primary carbocation (1°) or a tertiary carbocation (3°). The structure can be represented as:
\[ \text{CH}_3 - \text{C}^+ - \text{CH}_3 - \text{CH}_2 \]

### Step 5: Evaluate carbocation stability
The primary carbocation is less stable than the tertiary carbocation. Therefore, a methyl shift will occur from the adjacent carbon to stabilize the carbocation. This results in the formation of a more stable tertiary carbocation.

### Step 6: Rearrangement to form the stable carbocation
After the methyl shift, the structure will look like this:
\[ \text{CH}_3 - \text{C}^+ - \text{CH}_3 - \text{CH}_2 \]

### Step 7: Elimination of a proton (H)
Now, a proton (H) will be eliminated from the carbon adjacent to the carbocation, resulting in the formation of a double bond.

### Step 8: Write the final alkene product
The final alkene product formed from this reaction is:
\[ \text{CH}_3 - \text{C} = \text{CH} - \text{CH}_3 \]
This structure corresponds to 2-methylpropene.

### Final Answer
The major alkene formed from the reaction is **2-methylpropene**.

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