McLaurin Method (aka: The Rock-On Method)
Organic Chemistry → Stereochemistry → Isomers → Stereoisomers → Enantiomers → Determining RS Configurations
The Best Method for naming Enantiomers
(Absolute Configuration/RS Configuration/RS Nomenclature)
Title of Method: The McLaurin Method - Determining Absolute Configuration with Maximum Separation
aka: The Rock-On Method - Determining Absolute Configuration with Maximum Separation
Named due to Avril Lavigne's arrangement of her hand and fingers forming the Rock-On hand gesture demonstrated in
Figure 2-c. The Rock-On hand gesture is one of Avril Lavigne's favorite hand gestures.
Authors name: Timothy (Tim) McLaurin
Institutional Addresses: Independent Work - Earned 430 semester hours, at nine (9) Universities, over a 26 year 4 month span, from age 18 to age 44
A bit of Trivia: The 430 semester hours I earned is claimed as the United States and World Record, is it?
In addition, the 430 semester hours I earned at nine (9) different universities, is claimed as the current
United States and World Record, is it? If not, send me a message at Tim@StereoChemistry.net.
Professors who would like to read about this method in Journal format with a list of references: Click Here
Professors who would like to print the method for themselves or their students, please send me an e-mail (Tim@StereoChemistry.net), and I will provide a separate website to print from. The method is FREE for professors to print or download!
The method addresses the following problem that students frequently encounter when first confronted with Absolute Configuration (RS Configuration):
Beginning students have found it confusing and difficult to determine the 'Absolute Configuration' of a stereocenter when the lowest priority group is not directed away. Students'
attempts to mentally rotate the structure, in order to view the three highest priorities and thus determine 'Absolute Configuration', has been described as traumatizing by students. The
ability to mentally visualize and rotate a chemical structure takes practice, usually requiring a model. The authors of every chemistry textbook, college and high school level, have written
in their textbooks, practice with a model. All college chemistry professors and high school chemistry teachers state to the beginning student, practice with a model. The model
represents the tetrahedral shape, that of a carbon element with four different elements bonded to it. The following method, is the first method to specifically mimic the tetrahedral shape
of a stereocenter, as much as humanly possible. By using a method that depicts (resembles) that of the tetrahedral shape, the student is provided with the best resources (method and
model) to not only determine the 'Absolute Configuration', yet to mentally conceptualize and rotate the structure. All the published methods using three fingers, hand and arms, do not
take into account that the method itself, should look like (mimic) the tetrahedral structure, as does the following method. In addition, students can use this method while taking a quiz,
exam or final exam.
McLaurin Method (aka: The Rock-On Method)
(The photo's are of my hand. I understand it is not the most aesthetically pleasing hand, yet I am looking for volunteers.)
The method requires one hand, either the right or the left hand. The following Figures and examples will demonstrate the method using the right hand. The fingers used with the method are the thumb, index finger, and the pinky finger. Students need to assign priority to the four groups bonded to the stereocenter (chiral carbon) and then place the priorities to the corresponding fingers and the arm. The fingers (thumb, index finger, and the pinky finger) are outstretched from the hand as illustrated in the following photo.
A. The fingers (digits) outstretched from the right hand.
B. Examples Showing Relationship of Prioritized Groups to Arm and Fingers.
The four examples illustrate the assignment of fingers and arm in relation to the prioritized structure. The four examples have one chiral carbon with four different groups bonded to it. The four groups have been assigned a priority number according to the Cahn, Ingold, Prelog (CIP) sequence rules. The photo to the right of each structure represents the starting position of the method and has the prioritized groups already assigned to the fingers and arm.
The orientation of the structures in the following four examples is that so the starting position of the hand can easily be aligned with the
3-dimensional structure. The three dimensional structure is that of an upside down tripod with the thumb, index finger, and the pinky finger extended
upwards and outward. If one thought of making a fist with their hand and placing the hand in the place of the chiral carbon and extended the three fingers
(the thumb, index finger, and the pinky finger) upward and outward to represent methyl, bromine, and hydrogen respectively, as illustrated in Figure 1-b,
then the viewer would find that the three groups would be represented by the three fingers of the method. The arm would be the group extending downward,
the chlorine. The priority sequence determined for the four groups would be assigned to the corresponding fingers (thumb, index finger, and the pinky
finger) and arm, thereby assigning the priority sequence to the fingers and arm. Once the fingers and arm have an assigned priority sequence it is a matter of
viewing the fingers and arm so that the 1-2-3 priority sequence can be observed by the viewer, of which, may require rotating the hand to view the 1-2-3
priority sequence, as illustrated Figures 1-b, 2-b, 3-b, and 4-b. The following examples have been prioritized and the photo to the right of the structure has
the fingers and arm already assigned a priority. Note: the highest priority is represented by the number 1 and the lowest priority is represented with the
C. Viewing the 1-2-3 priority sequence of the hand model by the appropriate rotation of the hand, and determining the absolute configuration.
The following four examples illustrate the rotation of the hand to appropriately view the 1-2-3 priority sequence, with the lowest priority group, 4, directed away from the viewer. The viewer then decides the direction of the priority sequence and determines the configuration of the stereocenter.
D. Using the McLaurin Method with a Fischer Projection.
When determining absolute configuration of Fischer Projections, the method requires the arm to always be designated as the bottom vertical group. The thumb and index finger represent the groups to the left and right of the horizontal line, respectively. The pinky finger is designated as the vertical line above the stereocenter and the hand mimics as the stereocenter (chiral carbon).
E. Determining the absolute configuration from Natta Projections.
When orientations that do not have a specific vertical and horizontal illustration of groups (for example, Fischer projections and three-dimensional structures) the arm represents the bottom right group of the structure in question (the bottom right group is only for convenience: the method can determine the correct absolute configuration when the arm represents any group). The arm is assigned to the bottom right group, therefore the pinky finger is assigned one of two positions depending upon which group the arm represents. When the arm represents a group that lies on the plane of the paper the pinky finger always represents the group that lies behind the plane of the paper (Figures 1-e and 2-e). When the arm represents the group that lies behind the plane of the paper and keeping the fingers in the starting position as depicted in Photo-1, the pinky finger represents a group that lies on the plane of the paper (Figure 3-e). The thumb and the index finger always represent groups that are left and right of each other, respectively.
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 which 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 either of the commonly used representations of the three-dimensional geometry: 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. The method facilitates the studentsí 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 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 1981-1982, 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. Once, I stopped to ask the secretary in the administration building, if I could speak with Dean Corbett, and she said it would be few hours. That was the last time I asked the secretary if I could speak (visit) with Dean Corbett, for the next year and a half, I just walked past her and knocked on Dr. Corbett's door, and when he saw me, he said something like, 'What's going on', and I walked in and sat down, and we just talked for 20-30 minutes about all sorts of stuff, including the weather, during my two years of basic sciences. 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.
To view the method with a list of references (click here)
To view the 'Comparison of all Methods' (there a 6 methods) that have been published using fingers, hands and arms
and this method
Using the method with various molecular representations, click on the examples you would like view.
(Best viewed with Internet Explorer.)
A. Determining the RS Configuration's of: 3-Dimensional Formulas
B. Determining the RS Configuration's of: Fischer Projections
C. Determining the RS Configuration's of: Ring Formulas
D. Determining the RS Configuration's of: Newman Projections
AbsoluteConfiguration.Org - RSnomenclature.Org - RSconfiguration.Org
AbsoluteConfiguration.com - RSnomenclature.com - RSconfiguration.com
Future Chemistry and Organic Chemistry Websites
(Orgo Chemistry = Organic Chemistry)
(OChem = Organic Chemistry)
1. are isomers 1. are isomers
2. same molecular formula 2. same molecular formula
3. are stereoisomers 3. are stereoisomers
4. same connectivity 4. same connectivity
5. identical with its mirror image 5. not identical with its mirror image
6. superposable on its mirror image 6. non-superposable on its mirror image
7. has a 'plane of symmetry' 7. does not have a 'plane of symmetry'
8. achiral 8. chiral
9. mirror symmetric 9. dissymmetric
10. no 'handedness' 10. has 'handedness'
11. different chemical and physical properties 11. same chemical and physical properties
12. no optical activity 12. optically active (aka: optical isomers)
13. no tetrahedral center 13. has a tetrahedral stereocenter
14. could be sp3 hybridized, yet not tetrahedral 14. sp3 hybridized (chiral carbon is sp3)
15. more than one stereocenter, could be an enantiomer 15. when a stereocenter exists, it is an enantiomer
16. EZ, Cis-Trans or Syn-Anti nomenclature 16. RS nomenclature (Absolute Configuration)
17. Cis isomers have a dipole moment (polar) 17. D,L or d-l nomenclature (outdated)
18. Trans isomers have no dipole moment (non-polar)
Diastereomers versus Enantiomers
Empirical Formula (EF)
Molecular Formula (MF)
Plane of Symmetry
*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:
1. Solomons, T. W. G.; Fryhle, C. B. Organic Chemistry, 9th ed.; Wiley: New York, 2008; pp. 188-189, 214.
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.
Tim McLaurin is the Webmaster and Web owner.
Copyright © 2004-2011