I'm a little confused regarding D/L configurations for naming enantiomers of carbohydrates. The textbook only says that the absolute Fischer projection is drawn and if the OH is on the right it is a D-configuration and if it is on the left it is an L-configuration. However, the diagrams in the textbook showing this don't seem to put the lowest priority group on the top of the absolute Fischer projection(which I thought was necessary). Without sticking to this rule, it seems to me like for any given configuration we can perform a 180 degree rotation of the paper which shouldn't change the stereoisometry but only change the Fischer projection such that left swaps with right and up swaps with down which would swap the D/L configuration. For example in the picture if we performed the rotation on D-glyceraldehyde the new fischer projection would have OH on the left, CH2OH on the top, H on the right and CHO on the bottom and would become L-glyceraldehyde. Obviously a simple rotation shouldn't change the D/L configuration so what am I missing here? Is there some rule to drawing the absolute Fischer configuration that I'm missing?
mirror
1 !
CHO
CHO
1 1 1
H
OH
OH
-H
CH,OH
CH,OH
1
D-glyceraldehyde
L-glyceraldehyde