Question

How can I convert 3S,4R-dibromoheptane to a Fisher projection?

Answer 1

Step 1. Start with the wedge-dash structure of (`3S,4R`)-3,4-dibromoheptane.

Step 2. Convert the wedge-dash to a Fischer projection.

(a) Arrange the molecule so that the chiral carbons and the longest continuous chain are in a vertical arrangement. C-3 goes above C-4. Draw horizontal lines to make crosses at C-3 and C-4.

(b) Put the C-3 Br atom on the correct side of the cross.

View the molecule from an angle that puts C-3 closest to our eye and C-1 at the top (the upper right). The Br atom is on the right

Put the Br on the right arm of the cross. The H atom goes on the left.

(c) Put the C-4 Br atom on the correct side of the cross.

We must now view the molecule from the lower right. The Br atom is on the right.

We put the Br on the right arm of the cross. The H atom goes on the left.

And this is the Fischer projection of (`3S,4R`)-3,4-dibromoheptane.