How does the (R)/(S) method work to convert Fischer projections to bond line views?

1 Answer
Jan 29, 2015

A bond-line view gives no stereochemical information. I presume that you want to convert a Fischer projection to a wedge-dash view using (#R"/"S#) information.

Step 1. Start with the Fischer projection of D-glucose.

upload.wikimedia.org

Step 2. Convert this to a "bow tie" view by making all the horizontal bonds into wedges.

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Step 3. Assign configurations to the chiral carbons.

The assignments are #(2R,3S,4R,5R)#.

Glucose is #(2R,3S,4R,5R)#-2,3,4,5,6-pentahydroxyhexanal.

Step 4. Draw the wedge-dash structure.

Draw a trial zig-zag structure. Arbitrarily make all the H bonds wedges and the OH bonds dashes.

Some of them will be correct. Others won't.

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Assign configurations to the chiral carbons.

The assignments are #(2R,3S,4R,5S)#. Oops! Number 5 is wrong. We must interchange the wedge and dash.

We get

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This is the wedge-dash structure of glucose.

Step 6. (If you really wanted this) Convert to a bond-line structure.

Omit the H atoms on the chain and convert the wedges and dashes to solid lines.

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This structure could represent any of the 16 aldohexoses.