Step 1: Understanding the Concept:
Dehydrohalogenation follows Zaitsev's rule (Saytzeff rule), which states that in an elimination reaction, the preferred product is the alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms. Step 2: Key Formula or Approach:
The ease of formation of alkenes matches their thermodynamic stability:
Tetrasubstituted > Trisubstituted > Disubstituted > Monosubstituted. Step 3: Detailed Explanation:
Let's count alkyl groups attached to the \(\text{C=C}\) unit:
- (A) \(\text{R}_2\text{C=CH}_2\): 2 groups (Disubstituted).
- (B) \(\text{RCH=CHR}\): 2 groups (Disubstituted).
- (C) \(\text{R}_2\text{C=CHR}\): 3 groups (Trisubstituted).
- (D) \(\text{R}_2\text{C=CR}_2\): 4 groups (Tetrasubstituted).
The tetrasubstituted alkene (D) is the most stable and thus formed most easily and quickly according to the Zaitsev rule. Step 4: Final Answer:
\(\text{R}_2\text{C = CR}_2\) is formed most easily.