How can I draw Fischer projections from wedge and dash?
Here's how I do it.
We must view a wedge-dash formula from the correct angle to convert it to a Fischer projection.
Here's the wedge-dash structure.
We now view the molecule with
If we are viewing from above, we must mentally rotate the bonds so that
When we do this, the wedges become dashes, and the dashes become wedges, as in the picture below.
We don't rotate
The wedge-dash formula now looks like the one in the image below (I cropped it from here).
The wedges are now on the right, and the dashes are on the left.
It is as if we had wrapped the chain around a cylindrical tube.
When you flatten the structure onto the surface of the cylinder, you get the Fischer projection of D-glucose.