Consider 1-bromopropane (CH3CH2CH2Br) (a) Draw a Newman projection for the conformation in which !CH3 and !Br are anti (dihedral angle 1808). (b) Draw Newman projections for the conformations in which !CH3 and !Br are gauche (dihedral angles 608 and 3008). (c) Which of these is the lowest energy conformation? (d) Which of these conformations, if any, are related by reflection?

a. To draw a Newman projection we draw a circle for the rare carbon and and put a dot in center of circle for the front carbon. For a dihedral angle of 180° we put the respective groups opposite to each other making an angle of 180°.

b. For a dihedral angle of 60° Just rotate the conformation of dihedral angle 180° to anti clock wise up to 120°.

For a dihedral angle of 300° Just rotate the conformation of dihedral angle 180° to clock wise up to 120°.

c. The lowest energy conformation is the conformation having dihedral angle 180°. Because in this conformation the bulky groups are anti to each other.

d. Conformations having dihedral angle 60° and 300° are reflection of each other.