JEE MainChemistryGeneral Organic Chemistry
Consider the following pairs of molecules, represented by the groups attached to their central chiral carbon in a Fischer projection (given in the order: Top, Bottom, Left, Right). Which of the following pairs represents a pair of enantiomers?
Options
- AMolecule I: Top = - CH ₃ , Bottom = - C ₂ H ₅ , Left = - H , Right = - OH Molecule II: Top = - H , Bottom = -
- BMolecule I: Top = - CH ₃ , Bottom = - C ₂ H ₅ , Left = - H , Right = - OH Molecule II: Top = - C ₂ H ₅ , Botto
- CMolecule I: Top = - CH ₃ , Bottom = - C ₂ H ₅ , Left = - OH , Right = - H Molecule II: Top = - H , Bottom = -
- DMolecule I: Top = - CH ₃ , Bottom = - C ₂ H ₅ , Left = - OH , Right = - H Molecule II: Top = - C ₂ H ₅ , Botto
Correct answer
A. Molecule I: Top = - CH ₃ , Bottom = - C ₂ H ₅ , Left = - H , Right = - OH Molecule II: Top = - H , Bottom = -
Step-by-step solution
To determine the relationship between the molecules, we assign the absolute configuration (R/S) to each molecule using Cahn-Ingold-Prelog (CIP) priority rules. The priorities of the groups are: - OH (1) > - C ₂ H ₅ (2) > - CH ₃ (3) > - H (4). For Option 1: Molecule I: Top = - CH ₃ (3), Bottom = - C ₂ H ₅ (2), Left = - H (4), Right = - OH (1). The sequence 1 2 3 (Right Bottom Top) is clockwise. Since the lowest priority group ( - H ) is on a horizontal bond, the configuration is reversed from R to S. Molecule II: To