Methods Determining Absolute Configuration | RS Configurations using 3 fingers

Organic Chemistry → Stereochemistry → Isomers → Stereoisomers → Enantiomers → Stereocenters

The McLaurin Method

(aka: The Rock-On Method)

The Fastest, Easiest, Simpliest and most Realistic Method for Determining

Absolute Configuration | RS Configurations

 

 

A. Method Comparisons


In 1976, Thoman (18) developed and published in the Journal of Chemical Education, the first method using three (3) fingers, hand and arm to determine absolute

configuration. Since that time, five more methods using three fingers, hands and arms to determine absolute configuration, have been published in the Journal of

Chemical Education (JCE). The five developers (authors) of the other methods are, in chronological order, Garret, Beauchamp, Mattern, Huheey and Siloac. The

following chart notes those six developers (Academic Scholars) and their method's essential parts including the essential parts of the method described in this

manuscript.

 

The following chart represents the only methods (six of them) published in the Journal of Chemical Education requiring three (3) fingers,

hand(s) and arm(s), in addition to, the method I developed.

 

Thoman
1976
1st method

published 

Garret
1978
2nd method

published

Beauchamp
1984
3rd method

published 

 Mattern
1985
4th method

published

Huheey
1986
5th method

published 

 Siloac
1999
6th method

published

McLaurin
2004-2014
7th Method 

 Uses both

left and right

hands

 Uses both

left and right

hands

 Uses both

left and right

hands

 Uses both

left and right

hands

 Uses both

left and right

hands

 *Uses either the

right or

left hand

 *Uses either the

right or

left hand

 Uses the first three (3) fingers
(thumb, index and middle fingers)

 Uses the first three (3) fingers
(thumb, index and middle fingers)

 Uses the first three (3)     fingers
(thumb, index and middle fingers)

 Uses the first three (3) fingers
(thumb, index and middle fingers)
 Uses the first three (3) fingers
(thumb, index and middle fingers)

 Uses the first three (3) fingers
(thumb, index and middle fingers)

 *Uses the thumb, Index and Pinky finger
 The arm is pre-

assigned the 4th

priority group
 The arm is pre-

assigned the 4th

priority group

 

The arm is pre-

assigned the 4th

priority group
 

The arm is pre-assigned

the 4th priority group. 

In addition, the thumb,

index and middle finger

are assigned priority

groups 3, 2, and 1,

respectively.

 

The arm is pre-assigned

the 4th priority group.

In addition, the thumb,

index and middle finger

are assigned priority

groups 3, 2, and 1,

respectively.

 

*No predetermined

assignment of priority

groups to specific

fingers
 

*No predetermined

assignment of priority

groups to specific

fingers
 

Thoman, Garret, and

Beauchamp's methods

are the same!

In other words,

methods

1, 2 and 3

are identical,

that is, the steps are the

same!
 

Thoman, Garret, and
Beauchamp's methods
are the same!

In other words,
methods
1, 2 and 3

are identical,

that is, the steps are

the same!

 

Thoman, Garret, and Beauchamp's methods are the same!

In other words,

methods

1, 2 and 3

are identical,

that is, the steps are the

same!

 

Mattern and Huheey's
methods are the same!

In other words,

methods

4 and 5

are identical,

that is, the specific

fingers are assigned

the same priority

sequence, thus the

steps are the same!

 

Mattern and Huheey's
methods are the same!

In other words,

methods

4 and 5

are identical,

that is, the specific

fingers are assigned the

same priority

sequence, thus the

steps are the same!

 Siloac's method is different by using one hand, not the two (2) hands as required by the first five (5) methods, yet still uses the first three (3) fingers!

 First, the McLaurin method is different due to the different set of fingers (thumb, index and Pinky fingers) used, of which, are different than the previous six methods developed and published.

Secondly, using the thumb, index finger and pinky fingers increases the students 'stereoperception', thus allowing the student to visualize the hand and digits as a tetrahedral shape more so, than any of the previous methods.

The method's advantages parallels the tetrahedral shape the model takes on. All textbooks and professors, tell their students to practice with a model, it just makes sense to use a method that accounts for the tetrahedral shape, as well.

 

 Chart-1

 

 

Photo-222                     Photo-333

                                                            Photo-2                                                                                          Photo-3

 

 

 

          The first six methods, listed in Chart-1 from left to right, using three fingers, hand and arm to mimic the tetrahedral carbon, of which are published in the

Journal of Chemical Education, require the student to use their first three fingers, hand and arm, as depicted in photo-2. The seventh method, last column in

Chart-1, is the first to use the three fingers as depicted in photo-3. The first five methods in Chart-1, assign the 4th priority group to the arm. Designating the arm

with the 4th priority group, requires the student to move their elbow vertically, as much as 70 degrees depending on the location of the 4th priority group.

Therefore, the first five methods trying to mimic the tetrahedral shape of a stereocenter, have more mechanical parts. Those methods are requiring the student to

use their elbows and shoulders, in addition to their fingers, hands and arms. The sixth and seventh methods, last two columns in Chart-1, do not require the

student to engage in such contortional movements of the arm, elbow, and shoulder, yet a simple rotation of the hand to the correct position, in which the student

can determine the absolute configuration of the chiral carbon.  Yet, again the sixth method uses the first three fingers unsuccessfully mimicking the tetrahedral

shape of the stereocenter. The seventh method accounts for the tetrahedral shape of the stereocenter by using the thumb, index finger and the pinky finger, of

which, no method has been published noting that the tetrahedral shape of the method (hand model) is significant. In addition, the mental challenge encountered

by the student when working with the seventh method versus the first six methods, is significantly decreased by using the thumb, index finger and the pinky

finger. It is much easier to conceptualize and teach the tetrahedral shape and determine absolute configuration of a stereocenter using the pinky finger

(spanning the entire wrist) versus the third phalange (spanning 3/5ths of the wrist).

          After the student works through four or five structures (stereocenters), the student will not need to mark his/her fingers, yet will have begun to develop the

ability to visualize the 3-dimensional (tetrahedral) shape of the method in relation to the prioritized structure. For example, when the 4th priority group is directed

downwards it could be assigned to the arm, the thumb and index finger could represent two groups facing upward and out of the plane of the paper and the pinky

finger could represent the group going into the plane of the paper, then the student begins to develop an excellent 3-dimensional imagery of stereocenters in

comparison to the six methods that have been published in the Journal of Chemical Education. By spanning the entire width of the wrist using the thumb to the

pinky finger, the student recognizes the tetrahedral shape faster than any method previously developed and published.

 

Conclusion


The method described in this manuscript for assigning R,S-configuration, is the first method in which either hand can be used as a chiral template and makes

use of the pinky finger. By doing so, the method provides a clearer approximation of the actual three-dimensional shape of the tetrahedral geometry. As

demonstrated above, the method works equally well for any molecular representation of the three-dimensional geometry, including Fischer Projections or Natta

(wedge-dash) projections. Absolute configuration from the Fischer Projections is easily determined by the method without exchanging groups as required by the

exchange rules (6). The method facilitates the students' ability to successfully mentally rotate structures over a shorter period of time by using a method that

accounts for the tetrahedral shape. Students will always find conceptualizing spatial arrangement in three dimensions to be challenging. The method described

in this manuscript is a fast, comprehensive, reliable and a rapidly learned method for students to use whenever they need the assistance of a 3-dimensional

model.  I developed the method so that students could learn this critical content of Organic Chemistry with little difficulty. I find this method to be the most useful

and simplest method that has been published or presented to the Journal of Chemical Education. Students should find it very easy to use a method noting the

tetrahedral shape, while using one hand versus the traditional two hand methods, when taking exams and studying.

 

Hyperlinks to the Journal of Chemical Education (JCE) - The six methods (using fingers, hand and arm) listed above, in the method comparison chart, are

listed below with hyperlinks to the JCE for quick reference (must be a member of the JCE for free access).

 

1st method: 1976 - Thoman Method - University of Scranton: http://pubs.acs.org/doi/abs/10.1021/ed053p502.4
2nd method: 1978 - James Garrett - Stephen F. Austin State University: http://pubs.acs.org/doi/abs/10.1021/ed055p493
3rd method: 1984 - Phillip Beauchamp - California State Polytechnic University: http://pubs.acs.org/doi/abs/10.1021/ed061p666
4th method: 1985 - Daniel Mattern - University of Mississippi: http://pubs.acs.org/doi/abs/10.1021/ed062p191
5th method: 1986 - James Huheey - University of Maryland: http://pubs.acs.org/doi/abs/10.1021/ed063p598
6th method: 1999 - Edward Siloac - University of Virginia: http://pubs.acs.org/doi/abs/10.1021/ed076p798

 

The question must be addressed: Would the method that best mimics the tetrahedral shape of the molecule, in regards to the beginning student trying to

learn the difficult mental task of visualizing the 3-dimensional spatial arrangement of a stereocenter, be the 'Method of Choice', to teach or mention to

students, specifically when covering the topic of stereochemistry/isomers/stereoisomers/enantiomers/the assignment of R and S configurations to

stereogenic centers (stereogenic/chiral carbons)?

 

Other noteworthy methods are listed below, yet all 15 methods fail to demonstrate, with distinguishment, a real 3-dimensional spatial arrangement, that is,

the four bonded elements/groups to the carbon element. Thus the 15 methods are more confusing and time consuming in their approach to determining the

RS configuration's versus any method using three (3) digits (phalanges), hand and arm. Yet, the 15th method is understood as a staple in the teaching

process of many professors, and certainly Organic Chemistry textbooks.  The method presented on this website (webpage), is best method suited to mimic

the tetrahedral shape of the molecules stereocenter, due to the designated digits (thumb, index finger pinky finger), better than any method mentioned in this

article, on this website or any published method, journal or textbook.

 

1. Complementary Rules to Define R or S Configurations: 1972 - Cori - University of Chile, Chile:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed049p461

2. Facile Assignment of R,S Designations to Fischer Projections: 1980 - Price - Marshall University:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed057p528.3

3. A Simple Method for Specifying the R/S Configuration about a Chiral Center: 1982 - Idoux - University of Central Florida:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed059p533

4. Absolute Configuration in a Fischer Projection - A Simple Approach: 1983 - Bhushan and Bhattacharjee - University of Roorkee, India:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed060p191

5. Absolutely "Simple" Configuration in Fischer Projection Formula: 1983 - Reddy - University of Roorkee, India:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed066p480

6. The Flat and Direct Way to Rand S Configurations: 1983 - Brun and Leblanc - University of Moncton, Canada:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed060p403

7. A New Gimmick for Assigning Absolute Configuration: 1983 - Ayornide - Howard University:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed060p928

8. The Determination of Chiral Molecule in Fischer Projections: 1984 - Epling - University of Connecticut:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed059p650

9. The R/S System - A Method for Assignment and some recent modifications: 1985 - Eliel - University of North Carolina:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed062p223

10. An Astonishing Easy Method for Determining R and S for Fischer Projections (aka: 1-2-5 Rule): 1987 - Ruekberg - University of Rhode Island:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed064p1034

11. The Triangle Method: 1992 - Yongsheng and Cailan - Henan Normal University, China:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed069p273

12. The Rule of Multiplication: 1992 - Wang and Yang - Northwest Normal University, China:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed069p373

13. Grasping the Concepts of Stereochemistry (aka: The "Right-Hand Rule" of Organic Chirality): 1994 - Barta and Stille - Michigan State University:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed071p20

14. The Use of Stick Figures to Visualize Fischer Projections: 2001 - Starkey - California State Polytechnic University:
                                                                                                                                                     http://pubs.acs.org/doi/pdfplus/10.1021/ed078p1486

15. The "Steering Wheel" analogy, of which, is in every college Organic Chemistry textbook.

 

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.

 

Written permission needs to be obtained from
Tim McLaurin for reproduction and duplication.

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