Thanks with regards for your answers.

For a hexose, you’re looking at the C-5 stereocenter which is (R) for the D-sugars. When the hexose is drawn as a nice six-membered ring with the C1-c2-c3-c4- numbered clockwise (99% of cases, i.e. anomeric C-1 carbon on the right) if the C-5 CH2OH points up, it’s D and if it points down it’s L.
Things get more complicated if the hexose is drawn in its pyranose form. You need to determine if C-5 is (R) or (S).

For pentoses, you have to look at the C-4 chiral center.

I’m not aware that we fully understand what makes humans left- or right-handed in the first place, so your guess is as good as mine.

Good question. It’s a naming convention, so at some level it becomes, “because X says so! ” rather than a physical explanation.

However, it is wiser than at least one alternative. If it were the asymmetric carbon *nearest* the aldehyde that determines D/L , that would pose serious problems as the C-2 carbon’s configuration can change through “epimerization” (i.e. formation of an enol/enolate followed by protonation). As “D” and “L” denote “absolute configuration” and therefore define a pair of enantiomers, this would be a bad protocol if changing one chiral center (e.g. flipping C-2 of glucose to give mannose) resulted in switching the name from D- to L- .

I don’t know if this answers your question, feel free to drill down to something more specific.

(Yeah, google it, there’s lots of this happening.)