Question

Will a 1:1 mixture of these two compounds rotate plane polarized light? 19 O A. No OB. Yes

Answer 1

Ū ... (R) Br (s) /R) V (R) a (2R,4R)-2-bromo-4-chloropentane (2S,4R)-2-bromo-4-chloropentane YES 1:1 mixture of these two compounds will rotate plane polarized light. This is because they are diastereomers. Hence they do not have equal and opposite rotation.

R-S Nomenclature - Absolute configuration The designation of the absolute stereochemistry of any optically active compound according to this system involves the following steps: 1. A priority no such as (1), (2), (3) and (4) is assigned to each of the four atoms or groups of atoms attached to the chiral carbon n accordance with the following sequence rules. i. If the four substituent attached to the chiral carbon are all atoms, their priority no's. are decided on the basis of their atomic no's. The atom of higher atomic no. gets the higher priority. ii. If the relative priority of the two groups attached to the chiral carbon cannot be decided on the basis of above rule, it may be decided by comparing the atomic no's of the next atoms in the groups iii. Each doubly bonded atom is duplicated and each triply bonded atoms is triplicated. 2. Once the order of the priorities of the four atoms or groups directly attached to the chiral carbon has been decided, the molecule is then oriented in space in such a way that the group of lowest priority is directed away from us. If in going from 1+ 2+ 3. the eye moves in a clockwise direction, the configuration is specified as R and if in the anticlockwise direction, the configuration is S.