Question #85ebf

A Carbohydrate has the general formula #C_x(H_2O)_y#

So it has to have two times as many hydrogens as there are as many oxygens and another number of carbons

All carbohydrates must also be either a polyhydroxy aldehyde or a polyhydroxy ketone. In both, you have a hydroxy, which is an alcohol. SO the carbohydrate would need to have an oxygen bonded to a hydrogen somewhere in the molecule. It would look like:

#-OH#

Before hydroxy, it says poly, so it needs a few hydroxyls. This also means that the Carbon Chain has to be bigger than just 1 or 2 Carbons Long.

You also have either a Aldehyde or a Ketone. An Aldehyde is an oxygen double bonded to a Carbon at the end of the chain, and a hydrogen is also bonded to the same Carbon.
This looks like:

(Where R is rest of Chain)

This can also be a Ketone which is an Oxygen double bonded to a Carbon anywhere in the middle of the chain.
This looks like:

(Where R' may be a different rest of chain to R)

Both of these have a #C=O#, which is a carbonyl.

So the two functional groups a carbohydrate needs are a hydroxyl (alcohol) and a Carbonyl (#C=O#)