Meso Carbohydrate and stereochemistry

[UIUCstudent]

So I feel like carbohydrates are anomalies to me. Is it true that hydroxyl on the right side of carbohydrates are always R? I feel like this rule might go awry for non-carbohydrates. Like when the terminal carbons get reduced by NaBH4 or put through the nitric acid test.

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[babystepsCA]

So I feel like carbohydrates are anomalies to me. Is it true that hydroxyl on the right side of carbohydrates are always R? I feel like this rule might go awry for non-carbohydrates. Like when the terminal carbons get reduced by NaBH4 or put through the nitric acid test.

You are right.For carbohydrates, when you draw fischer projection, if the hydroxyl on the last chiral carbon is on the right, the sugar is named D, which happens to be also R of this carbon. Of course, changing oxidation state of the carbon atoms will have impact on the R/S naming. In that case, to correctly assign R/S, you really have to determine one chiral center at a time.