Worked Example 21.1 Assigning R or S Configuration to a Fischer Projection Solution The priorities of the groups are(1)-NH2,(2)-CO2H,(3)- CH3,and (4)-H To bring the lowest priority(-H to the top we might want to hold the-CH3 group steady while rotating the other three groups counterclockwise Rotate 3 groups counterclockwise 2 4 CO2H H 1 H2N- -H4 same as 2H02C -NH21 CH3 CH3 3 Hold CH3 steady Solution ▪ The priorities of the groups are (1) –NH2 , (2) –CO2H, (3) – CH3 , and (4) –H ▪ To bring the lowest priority (–H ) to the top we might want to hold the –CH3 group steady while rotating the other three groups counterclockwise Worked Example 21.1 Assigning R or S Configuration to a Fischer Projection