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This is probably trivia for many of you (I already feel the pressure by even posting this question). Yet funny enough, most of the time the materials I have come across show the wedge-d/hash notation. Then due its cumbersome or what not, the material decides to propose Fisher project as a better notation. But frankly that doesn't give the proper picture of the stereochemistry or least understanding of how the atoms would arrange in space.

When revising Rectus-Sinister (R/S) system for stereochemistry, it has almost always indicated about assigning priority to the groups by descending order of the atomic number and that lowest priority substituent should always point away from the plane of the central atom. Speaking of a simple molecule like $\ce{CH4}$, Wedge-Dash is ideally suited to show structure of sp3 hybridised (tetrahedral atoms).

But what about more complex compounds/molecules like amino acids or things like drugs like morphine etc? or even an imaginary molecule given in exam? I dread at the thought of it.

I went through this question for few days now, before posting this question. Perhaps it has more advanced perspective compared to the simplicity of my question I think.

So are there direct guidelines to draw the wedge-h/dash notation for a given complex molecule? Am I really missing something from preliminary general chemistry here?

enter image description here

Obviously there are online applets that allow to get a SMILE of a molecule and generate the 3D structure like JSmol. I also know there are complex methodologies employed in higher level of physical science to determine the structure of molecules. But at this beginning level, is there anyway to determine the 3D structure of a molecule? At least to get a feeling of it, and to predict that what atom/side chain would pop out of plane and remain in the plane?

I am a beginner in Chemistry, so should I really bother about this at all?

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If not using a Fischer projection, structural formulae with hashes and wedges allow to be more specific.

In the structure drawn in your current question, you provide information about the connectivity of atoms within the molecule, up to a point to indicate if the bond between two atoms is a single, double, or (not present here) a triple / quadruple.

Using wedges and dashes, equally provides this information; however additionally informs the reader about the sterochemical relationship of the atoms bound around an atom in a centre, addressing a specific (R)/(S) configuration. Returning to your example, there are three sterogenic centres that I marked by an asterisk:

enter image description here

and for each centre you may find a pair of either configuration; for example for the hydroxyl group in $\alpha$ position to carbonyl alone

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In total (for 3 stereogenic centres), there are $2^3 = 8$ distinct stereoisomers possible with different properties, which all fit into the first "line only" general representation.

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  • $\begingroup$ Buttonwood, thanks for this! Perhaps you are not getting my question? If you give me this molecule, I wouldn't know how to draw wedges/hashes at this state. That's why I wanted to know if there's a checklist, guidelines that has reasoning and which can be followed. Also I have no issues with Fisher. What I mean was most books talk about Fisher as a substitute for wedge/dashes. But do not mention how to begin wedge/dashes. I personally prefer the latter, because it really gives me a good idea of the spatial arrangement/stereoisomerism, geometry etc. So guidelines please? :) $\endgroup$ – bonCodigo Jul 27 '17 at 22:24

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