Question

> Which of the following terms best describes the pair of compou diastereomers, or the same compound bes the pair of compounds shown: enantiomers, HC WOH HO eneantiomers 8) Label each asymmetric carbon in the compound below as R or S. OH "CH3 9) Label each asymmetric carbon in the compound below as Ror S. OH нуусна нсн OH 10) Label each assymetric carbon in the compound below as R or S. 11) Draw the structure of (2R,3S)-2,3-dichloropentane. Take particular care to indicate three- dimensional stereochemical detail properly. 12) Draw the structure of (S)-1-bromo-1-chloropropane. Take particular care to indicate three- dimensional stereochemical detail properly. 13) Draw the structure of a meso form of 1,3-dichlorocyclopentane. Take particular care to indicate three-dimensional stereochemical detail properly. 14) How many asymmetric carbons are present in the compound below?

Answer 1

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.

7) The stereochemistry of the chiral centres is shown below CH3 RN OH on H3C :: 111}}}OM HOM RR and SS isomers are ENANTIOMERS 0H 1

> IOH HOR) 9)The given conformer is which is equivalent to (25,3R)-butane-2,3-diol 10) CI