L X A R (SOUNDS LIKE ELIXER)

First, we will consider only D- sugars. If the next to last -OH is on the right; it is a D-sugar. Here are the four D- pentoses :

Note Carbons #4 and #5 on each (inside the blue box). They are all the same for a D- sugar.

Now comes a very easy way for remembering the structures. We need only consider carbons #2 and #3. From LXAR, R stands for ribose and right:

The OH groups of interest at 2 & 3 point to the right.

The L in LXAR stands for LYXOSE or #2 and #3 on the left.

X in LXAR stands for CROSS. X is also for XYLOSE.

The OH groups cross back and forth.

A in LXAR stands for ARABINOSE.

Use the process of elimination. It is the remaining possibility.

Now you should be able to recognize all 8 pentoses, four D- and four L-.

Note that each D,L pair are mirror images. Sometimes students make the mistake of just flipping the #4 carbon atom to go from D- to L- ; you flip them all. You would not convert a photo of your right hand into a photo of your left hand just by pasting over one finger with one cut from your left hand.