So... Should we believe Jane is next?
What's the difference between L-sugar and... a sugar molecule that you're looking at from the other side?
I understand why this question is oftenly asked. Considering this kind of representation of a molecule I would consider it is just seeing the same molecule from another point of view.
First of all, an L sugar is an enantiomer (mirror image) of the D sugar (L-Glucose and D-Glucose in the image). Optically, we would consider that changing the view of the L-Glucose would give the D-Glucose, but that's not the case. We have to (must) consider the spatial organization of atoms within a molecule.
In a molecule, each type of bond require an amount of space to stabilize the bonding of the atom. What I mean is: every valence electron that participates in a bond require a space according to the type of bonding (typically in C compounds, there are n, pi and sigma bonds depending if there is a single, double or triple bond) and, as consequence, all valence electrons distribute the space proportionally. For example a Carbon with 4 single bonds will have two bonds to the side, 1 pointing to the front and 1 to the back. Obviously this example is subdued to change if you change the point of view, but what I mean is 2 bonds are in the same plane.
Now, going back to the L sugar... Consider the next image with the D-molecule to the left and the L-molecule to the rigth (NOTE: this applies to all enantiomers):
As you can see in the image, the H, NH2, CH3 and COOH parting from the chiral carbon (central carbon in this case) mantain their respective bond representation (a black triangle represents a bond pointing to the front and the pointed line to the back). Now, if you change the point of view of the L-molecule as to overlap the position of H, NH2, CH3 and COOH of the D-molecule (seeing the L-molecule from behind), you would notice that, even though the functional groups are now in the "same" place, the spatial orientation of the NH2, CH3 and COOH is different (D-molecule has CH3 to the front and NH2 and COOH to the back while L-molecule is opposite).
I hope I could explain myself as to clarify any doubt about D and L molecules...
EDIT: GAH! I hate Wikipedia and its .svg images...