- AEclipse, Gauche, Anti
- BGauche, Eclipse, Anti
- CEclipse, Anti, Gauche
- DAnti, Gauche, Eclipse
View written solutionFree
Correct answer: C
-
Identify the molecule and the relevant conformations
2-fluoroethanol is .
Rotation about the bond gives three main conformations:- Eclipsed
- Gauche: and are staggered with dihedral angle
- Anti: and are opposite, dihedral angle
-
General stability of eclipsed vs staggered
Eclipsed conformations are usually least stable because of:
- torsional strain
- unfavorable eclipsing interactions
Therefore,
-
Compare Gauche and Anti in 2-fluoroethanol
Normally, for simple substituted ethanes, anti is more stable than gauche due to less steric repulsion.
However, in , the gauche conformation is especially stabilized. -
Reason for gauche stabilization
In the gauche form, and come close enough for favorable intramolecular interaction. This is commonly attributed to the gauche effect and can also be viewed as a weak intramolecular hydrogen-bonding/electrostatic stabilization between and .
Thus,
-
Overall increasing order of stability
Combining the above:
-
Match with options
- A: Eclipse, Gauche, Anti wrong
- B: Gauche, Eclipse, Anti wrong
- C: Eclipse, Anti, Gauche correct
- D: Anti, Gauche, Eclipse wrong
Therefore, the correct answer is:
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