Chemistry - STEREO ISOMERISM Question with Solution | TestHub
Different spatial arrangements of the atoms that result from rotation about a single bond are conformers. n-Butane has four conformers eclipsed, fully eclipsed, gauche and anti. The stability order of these conformers are as follows : Although anti is more stable than gauche but in some cases gauche is more stable than anti. Anti gauche Partial eclipsed Fully eclipsed
Which one of the following is most stable conformer :
Options:
Answer:
Solution:
Explain the question: Identify the most stable Newman conformer
Concept:
This question is based on conformational analysis and Torsional Strain.
Solution:
The molecule is 1,2-dichloro-1,2-dimethylethane. We compare the staggered conformations shown in the options.
Option 1: The CH3 groups are anti to each other, and the Cl atoms are also anti. This places the
largest groups at 180°, minimizing steric repulsion → most stable.
Option 2: Both CH3 –CH3 and Cl–Cl are gauche, causing maximum steric hindrance → less
stable.
Option 3: CH3 group is anti to Cl, but the other CH3 group is gauche to Cl. Although H–H are
anti, the largest groups (CH3 and Cl) are not in the most favorable anti-periplanar arrangement.
Hence, this conformation is not the most stable/optimal.
Option 4: Eclipsed conformation, hence least stable.
Conclusion:
Option 1 is the most stable conformation due to minimum steric strain.
Final Answer: Option (A)