Question about Straight Chain Sugars

[tablerule]

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How come straight chain sugars can't rotate about the Carbons that connect to each other in their single bonds. Can't single bonds rotate? I don't understand why they are fixed in place to have all the different types of sugar.

Can't wrap my head around it..

 

[theonlytycrane]

can you elaborate?

 

[popopopop]

I think he's asking why can't open chain carbs change conformation to other sugars, because they're single bonded carbon skeletons. He's asking why there are different isomers of sugars.

 

[aldol16]

The rotations should not give you another sugar. You can build it using a model and try it for yourself but once a stereocenter is set, you can't get to the other stereoisomer by simple rotation about sigma bonds.