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Count the stereoisomers of four sugars, each with an unbranched carbon chain: an aldotetrose (4…

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Count the stereoisomers of four sugars, each with an unbranched carbon chain: an aldotetrose (4 carbons), an aldopentose (5 carbons), an aldohexose (6 carbons) and a 2-ketohexose (6 carbons). Count the D and L forms together. Then say how many of the aldohexoses belong to the D series.

Need a reminder? The key ideaShow

A carbohydrate is a polyhydroxy aldehyde or ketone. An aldose has $n - 2$ stereocentres and a ketose has $n - 3$ , where $n$ is the number of carbons in the chain. The number of stereoisomers is $2^{\text{centres}}$ , and half of them belong to the D series. An empirical formula comes from the moles of each element in 100 g.

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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