MolDraw › Chemistry tools › Fischer Projection Converter
Fischer Projection Converter (Fischer ⇄ Wedge-Dash, R/S, D/L)
In short: Build a Fischer projection row by row, or paste a SMILES with @/@@ marks. The tool draws the Fischer projection and the wedge-dash structure, labels every stereocentre R or S with its CIP priorities, and gives D or L for sugars and amino acids.
Use it for glucose, threose, tartaric acid, amino acids and any open-chain molecule with up to five stereocentres in a row. The turn and swap buttons show which moves keep the molecule the same and which give its mirror image.
Or build the Fischer projection (top to bottom)
Examples:
Wedge = toward you, dash = away from you. The R/S labels on both drawings come from the same CIP analysis.
How to use the Fischer projection converter
- Paste a SMILES with
@/@@and press Convert, or press an example such as D-Glucose. - Change any group with the menus. The top menu is the top of the vertical chain; each row is one carbon with a left and a right group.
- Read the Fischer projection and the wedge-dash structure side by side. Each centre gets a card with its CIP priorities, where each group sits, and how R or S follows.
- Try Rotate 180° (same molecule), Rotate 90° (enantiomer, one centre only), Mirror image, or ⇄ on a row (inverts that centre).
Fischer projection rules
Horizontal = toward you
Every crossing point is a carbon. Horizontal bonds come out of the page (wedges). Vertical bonds go back into the page (dashes). The main carbon chain runs top to bottom, most oxidised carbon (CHO, COOH) at the top.
Rotate 180° is allowed
Turning the whole drawing 180° in the plane of the page keeps vertical bonds back and horizontal bonds forward. It is the same molecule.
Rotate 90° is not
A 90° turn puts the back bonds on the horizontal and the front bonds on the vertical. Read as a Fischer projection, it shows the enantiomer.
One swap inverts
Swapping any two groups on one carbon inverts that centre (R ⇄ S). Two swaps on the same carbon give back the original.
R/S straight from a Fischer projection
- Rank the four groups on the carbon by CIP rules (atomic number first; duplicate atoms for C=O).
- Trace 1 → 2 → 3 on the page.
- If group 4 (often H) is on a vertical bond, clockwise = R and anticlockwise = S.
- If group 4 is on a horizontal bond, reverse the answer.
D and L
Draw the chain with the most oxidised carbon at the top. For a sugar, look at the stereocentre furthest from the C=O: OH on the right is D, on the left is L. For an amino acid, look at NH₂ on the α-carbon: right is D, left is L. D/L compares a molecule with glyceraldehyde; it does not say which way the molecule rotates light, and it is not the same as R/S.
Fischer to wedge-dash (zigzag)
The Fischer projection shows every carbon in an eclipsed conformation, with the chain curling back behind the page. A zigzag drawing shows the chain staggered and flat in the page. Rotating every second carbon by 180° turns one into the other, so groups on the same side of a Fischer projection end up on opposite sides (one wedge, one dash) on neighbouring carbons of the zigzag. The tool does this conversion for you and checks the result with R/S.
Worked examples
L-Alanine
COOH top, CH₃ bottom, NH₂ left. NH₂ (1) > COOH (2) > CH₃ (3) > H (4). 1 → 2 → 3 is clockwise, H is horizontal, so reverse.
(S)-alanine; L because NH₂ is on the left
D-Glucose
OH right, left, right, right on C2 to C5. The last stereocentre (C5) has OH on the right.
(2R,3S,4R,5R), D-series
Tartaric acid
OH on the same side on C2 and C3: a mirror plane cuts the molecule between them. OH on opposite sides: chiral.
meso (2R,3S) and the pair (R,R)/(S,S)
Erythrose and threose
Erythrose has both OH on the same side; threose has them on opposite sides. They are diastereomers.
D-erythrose (2R,3R), D-threose (2S,3R)
Common mistakes
- Rotating a Fischer projection by 90°. It gives the enantiomer.
- Forgetting to reverse the answer when H is on a horizontal bond.
- Thinking D always means R. D-glyceraldehyde is R, but D/L and R/S are different systems; L-cysteine is R.
- Reading D/L from the wrong carbon. For sugars use the stereocentre furthest from the C=O, not C2.
- Copying a Fischer projection into a zigzag without turning alternate carbons: same-side groups in a Fischer projection become anti (wedge and dash) on neighbouring zigzag carbons.
The tool handles open chains with up to five stereocentres in a row. Stereocentres in a ring cannot be drawn as a Fischer projection.
Draw it properly. Open the structure in the free MolDraw editor to add wedges, labels and arrows, then export a PNG or SVG.
Open full MolDraw editorFrequently asked questions
What is a Fischer projection?
A flat drawing of a molecule with stereocentres. Each crossing point is a carbon. Horizontal bonds point toward the viewer and vertical bonds point away. The main chain runs from top to bottom.
How do I find R or S from a Fischer projection?
Rank the four groups by CIP rules and trace 1 → 2 → 3. If the lowest-priority group is on a vertical bond, clockwise is R. If it is on a horizontal bond, reverse the answer.
Can I rotate a Fischer projection?
You can rotate it 180° in the plane of the page and it stays the same molecule. A 90° rotation gives the enantiomer, because it puts back bonds on the horizontal.
How do I tell D from L?
Put the most oxidised carbon at the top. For a sugar, the OH on the stereocentre furthest from the C=O is on the right in D and on the left in L. For an amino acid, NH2 on the α-carbon is on the left in L.
Is D the same as R?
No. D/L compares the molecule with glyceraldehyde, while R/S comes from CIP priorities. D-glyceraldehyde is R, but L-cysteine is R and most other L-amino acids are S.
How can I spot a meso compound in a Fischer projection?
Look for a horizontal mirror line through the middle: if the top half is the mirror image of the bottom half, the molecule is meso and achiral. meso-Tartaric acid has both OH groups on the same side.
Is the Fischer projection converter free?
Yes. It runs in your web browser with no sign-up.
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