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

1 Answer
Ernest Z.
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.

enter image source here

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

enter image source here

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.

enter image source here

This structure could represent any of the 16 aldohexoses.

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