Ch. 5 - ChiralityWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

Concept #1: R and S rule for Fischer Projections.


Now that we're pretty familiar with Fisher projections it turns out that there's going to be a new way to determine R and S for them, the reason is because converting these structures to bond line and then figuring out our R and S would be pardon my French a bitch, alright? So what we want to do is want to figure out an easy way to figure out R and S and there actually is there's a shortcut that we can use so I want to go ahead and show you guys that right now, alright? So this is basically the way it works we want to determine the location of the lowest priority group, OK? what I mean by location is you want to figure out is it vertical or is horizontal, OK? If and the lowest priority group is always going to be 4 so basically I just want to know where is 4, OK? If 4 is vertical, OK? if 4 is faced vertical then the Chirality is exactly as it looks and I'm just going to go from 1 to 3 I'm going to draw that arrow and that's going to be it, OK? Whereas if 4 is horizontal, OK? Then the Chirality is just going to be flipped so wherever you draw you're just going to take the opposite sign, right? So here I have two examples this would be an example where H is vertical so notice that my fourth priority group is vertical so that means that it's going to be as it looks so I'm just going to say 1 to 2 to 3 it's going a S direction so that's actually going to be the final answer, the final answer for this Chiral's center would actually be S, does that make sense so far? Now let's look at this next one here's my Chiral center, 4 as you can see is now horizontal so that means it's going to be flipped so once again I'm going to do 1 to 2, 2 to 3, 3 to 1 it looks like S but it's actually going to be R because of the fact that it's horizontal, now keep in mind for Fisher projection I'm never swapping groups so I'm not swapping out 1 and 4 or anything like that all I'm doing is I'm just taking the chirality and I'm flipping it if it happens to be horizontal or I'm keeping it if it happens you vertical so in some ways this is actually easier than we learned for the other compounds and when you have a very big Fisher projection that has a lot of Chiral centers you're going to be thankful that you have this method that you can just go really really fast and figure it out, OK? So what I want you guys to do now is go ahead and determine the absolute configurations meaning the R and the S for this Fisher projection using this formula and using this format and then when you're done I'll go and show you guys how to do it.

Determine location of lowest priority group:

  • If vertical, chirality is as it looks
  • If horizontal, chirality is flipped.

Determine the absolute configurations for all chiral centers.

Example #1: Determine the absolute configurations for all chiral centers.

Name the following molecule.
Answer the following questions based on the compoud named.  a) Draw the Fischer projection of (2R,3S,5R)-5-bromohexa-2,3-diol.                 b) Name and draw two diastereomers of (2R,3S,5R)-5-bromohexa-2,3-diol.               c) Name and draw the enantiomer of (2R,3S,5R)-5-bromohexa-2,3-diol. 
Determine whether each statements is true or false: Rotating the Fischer projection of a molecule with a single chirality center by 90° will generate the enantiomer of the original Fischer projection:
What is the IUPAC name of the compound shown below? A) (2R,3S,4R)-3,4-dibromo-2-chloro-3-methylhexane B) (3S,4S,5S)-3,4-dibromo-5-chloro-4-methylhexane C) (2R,3S,4S)-3,4-dibromo-2-chloro-3-methylhexane D) (2R,3R,4S)-3,4-dibromo-2-chloro-3-methylhexane E) (2R,3S,4S)-2-chloro-3,4-dibromo-3-methylhexane
For each of the following pairs of molecules identify them as one of the following: constitutional isomers (I), same molecule (S), enantiomers (E), diastereomers (D), or none of the above (N).
What are the absolute configurations of these two molecules? a) S(I) and S(II) b) S(I) and R(II) c) R(I) and S(II) d) R(I) and R(II)
In the Fischer projection below determine the correct R/S designation for each chirality center [going from top (1) to bottom (3)].  
The configurations of the two stereocenters (chiral centers) in this Fischer projection are  a) 2R, 3R  b) 2R, 3S c) 2S, 3R  d) 2S, 3S
Draw the mirror images of the following molecules. Correctly identify the absolute configuration of each chiral center in both the molecules shown and their mirror images. Are any of these molecules superimposable on their mirror image?
Consider the compound below to answer the following questions:  Assign the configuration as (R) or (S) at each chiral center. Draw an acceptable regular three dimensional structure for the compound. Draw the structure of its mirror image and determine its relationship with the original molecule. Is the molecule chiral?
As shown below, compound (B) is one of the configurational isomers of (A). (a) Determine stereo‐configuration of the carbons in (B) (R, S, or none) and complete Fisher projection of (B). (C1 on the top) and cross points representing C2, C3, and C4. (b) Please fill in wedge/dash bonds and substituents in the blanks provided below to create the enantiomer (C) to the compound (B). And please also complete the drawing of two meso compounds (D) and (E) based on skeletal (A).
Circle the structure that represents (2S,3R)-2-bromo-2-chlorohex-4-yne-1,3-diol.
Determine the R and S configuration of the following compound. 
Draw the mirror image of the following molecule. 
Which statement about these Fischer projections is correct?a) I and III are enantiomers.b) II is a meso isomer.c) II and IV are identical.d) I and II are diastereomers.
Draw structural formulas for the three compounds shown below. Make sure to include all pertinent stereochemical information.
Draw Fischer projection formulas for all stereoisomers of 2,4-dimethyl-3-hexanol, giving stereochemical details for each structure. As a bonus, include which compounds are enantiomers of each other and which are diastereomers.