Determining the Absolute | RS Configurations of 3-Dimensional Examples
Organic Chemistry → Stereochemistry → Isomers → Stereoisomers → Enantiomers → Stereocenters

The McLaurin Method

(aka: The Rock-On Method)

The Fastest, Easiest, Simpliest and most Realistic Method for Assigning | Determining Absolute Configuration

Determine the Absolute Configurations of the 3-dimensional Practice Problems

3-Dimensional Examples

3-d-a1

Example A: 2-Butanol

3-d-1

3-d-2

Example B: 2-Chlorobutane

3-d-16

3-d-22

Example C: 2-Bromopentane

3-d-4

3-d-5

3-d-6

Example D: 1-Chloro-2-methylbutane

3-d-7

3-d-8

3-d-9

3-d-10

3-d-11

Example E: 2-Hydroxy-3-butene (But-3-en-2-ol)

3-d-12

3-d-13

3-d-14

3-d-15

 

 

Acknowledgments


I would like to acknowledge and thank the following for their time and effort: Denise for her help with her editing skills, Dr. and Mrs. Greever (Organic Chemists)

for making Organic Chemistry interesting and learnable when I was an undergraduate Organic Chemistry student in 1982-1983, the girls of Physical Therapy

(Zofia (Chairman of the Physical Therapy Department) Julie, Debbie, Sharon and Gloria) for making me realize my academic success and excellence is the

number one priority, aside from my nearly four (4) consecutive years of work with patients (not customers or clients) in the Physical Therapy Department

(while going to college full-time during the fall, spring and summer semesters, of 1980-1984). In addition, I would like to thank very much, the Chairman (Dean)

of the University of Mississippi Medical School, for providing me the inspiration and wisdom, at the end of every semester, to continue my undergraduate

studies to be a future physician, during the years of 1981-1984, in addition to the time Dr. Corbett (Dean of the Basic Sciences - Ross Medical School -

1994-1996) provided me, with my unannounced 20-30 minute visits to his office in the administration building, about every week or two, during my two years

of basic sciences in medical school. Dr. Corbett, for two years, never said he was too busy to talk with me. Dean Corbett and his wife, even asked me over

to their house, for supper many times! And last but least, a special thanks to Avril Lavigne for being instrumental and thus providing me with the key to the

development of this method and my parents for which none of this would have ever happened if it was not for their unyielding positive support,

that no other could equal.

 

Why was the Method developed?

When I took Organic Chemistry in 1982-83, I missed 80-85% of the questions related to determining the configuration(s) of enantiomers (that is,

RS configurations).  Of which, I still have my Organic Chemistry quizzes and exams from 1982-83. Twenty-one (21) years later, I wrote a review book on

Organic Chemistry and when I got to Stereochemistry, I remembered the trouble I had with determining/assigning RS configurations. As a result, I decided

to try to develop a method that would make it as easy as possible for students to determine/assign the correct configuration.

Most of my goals in the endeavor are as follows:

 

1. I decided that the following list contained most of the appropriate expectations of students.

     a. The method has to be as easy, fast and simple, as any method that has ever been published, if not better than all methods that have been published.

     b. The method should be used in the classroom during quizzes and exams, even on the medical college admission test (MCAT).

     c. The method should be as to scale as a 'Real' molecule (as similar to the model set as possible).

     d. The method should demonstrate the four (4) elements bonded to the chiral carbon.

     e. The method should help students develop their 'stereoperception' (the ability to visualize the 3-dimensional spatial arrangement of the molecule at and around

         the stereocenter and be able to mentally rotate the molecule), thus the use of the 'Pinky' finger, Index finger, Thumb and Arm, with the hand acting as the

         chiral carbon.

     f. The method should work with all molecular representations that show some 3-dimensional direction, for example, a dash or wedge, as well as, work with

        Fischer Projections.

     g. The method should only require the student to use one (1) hand for all the stereocenters of each chiral molecule, even if the molecule has two or more

         stereocenters.

     h. The method has to determine the correct configuration 100% of the time.

     i. The method should be easy to learn, use and remember.

     j. The method should be FREE for all students, faculty and others.

 

2. In addition, the method should not do the following.

     a. The method should not be a 'Trick of the Trade', for example, exchanging elements (groups). For this to happen in real life, bonds are broken and made,

         involving energy. In real life, this exchanging of elements (groups) does not occur. In addition, exchanging of elements does not help the student develop

         their 'Stereoperception', mental visualization of 3-dimensional spatial arrangement of the molecule(s) (chiral molecules).

     b. The method should not require two (2) hands to determine/assign an RS configuration, or multiple configurations on the same molecule (increases

         confusion).

     c. The method should not require the student to be a contortionist, in order to use the method.

     d. The method should not provide the opposite answer (aka: opposite configuration)!

     e. The method should not have been published in the Journal(s) by anyone, ever before.

 

*Historical Origin of Stereochemistry (1):

It was . . . Louis Pasteur's separation of a racemic form of tartaric acid in 1848 that led to the discovery of the phenomenon called enantiomerism. Pasteur, consequently, is considered to be 'The Founder of the field of Stereochemistry'. Pasteur's discovery of enantiomerism and his demonstration that the optical activity of the two forms of tartaric acid was a property of the molecules themselves led, in 1874, to the proposal of the tetrahedral structure of carbon by van't Hoff and Le Bel.

In 1877, Hermann Kolbe (of the University of Leipzig), one of the most eminent organic chemists of the time, wrote the following:

Not long ago, I expressed the view that the lack of general education and of thorough training in chemistry was one of the causes of the deterioration of chemical research in Germany . . . Will anyone to whom my worries seem exaggerated please read, if he can, a recent memoir by a Herr van't Hoff on "The Arrangements of Atoms in Space," a document crammed to the hilt with the outpourings of a childish fantasy . . . This Dr. J. H. van't Hoff, employed by the Veterinary College of Utrecth, has, so it seems, no taste for accurate chemical research. He finds it more convenient to mount his Pegasus (evidently taken from the stables of the Veterinary College) and to announce how, on his bold flight to Mount Parnassus, he saw the atoms arranged in space.

Kolbe, nearing the end of his career, was reacting to a publication of a 22-year-old Dutch scientist. This publication had appeared earlier, in September 1874, and in it, van't Hoff had argued that the spatial arrangement of four groups around a central carbon atom is tetrahedral. A young French scientist, J. A. Le Bel, independently put forth the same idea in a publication in November 1874. Within 10 years after Kolbe's comments however, abundant evidence had accumulated that substantiated the "childish fantasy" of van't Hoff. Later in his career (in 1901), and (also) for other work, van't Hoff was named the first recipient of the Nobel Prize in Chemistry.

Together, the publications of van't Hoff and Le Bel marked an important turn in a field of study that is concerned with the structures of molecules in three dimensions: Stereochemistry

Literature

1. Solomons, T. W. G.; Fryhle, C. B. Organic Chemistry, 9th ed.; Wiley: New York, 2008; pp. 188-189, 214.

 

 

Future Chemistry and Organic Chemistry Websites

StereoChemistry.net
StereoIsomer.com
StereoIsomers.net

ChemistryTerminology.com

 

 

NOTE: This method is copyrighted with the Library of Congress located in an Organic Chemistry Review Book, I wrote years ago.

 

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