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Can someone please tell what this model represents?

Answer 1

The model represents α-D-mannopyranose.

Your model shows a six-membered ring containing an oxygen atom.

Carbon 1 has both an ether and a hydroxyl group. It is part of a hemiacetal group (in the blue rectangle).

There is a hydroxyl group on every carbon, and the hydroxymethyl group on #"C5"# (in the red rectangle) is pointing "up."

The compound is the pyranose form of a D-aldohexose.

It may be easier to identify the compound if we "unwrap" the model and draw it as a Fischer projection.

Remember that "down" is to the right and "'up" is to the left in a Fischer projection.

We get

We compare the structure with those of the eight aldohexoses.

Our mnemonic tells us the compound is D-mannose.

Since the #"OH"# group on #"C1"# is down, the full name of the compound
is α-D-mannopyranose.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.