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Desymmetrization of the Tetrahedron: Stereogenic Centers
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Abstract
In undergraduate teaching, stereochemical issues in the molecule Cabcd, formed by an sp3 hybridized carbon atom bonded to four substituents, a, b, c, and d, are usually analyzed using drawings or molecular models that represent the molecules as regular tetrahedra with the substituents at the vertices. Strictly speaking, however, Cabcd can only have the geometry of a regular tetrahedron if all substituents are identical, as in methane CH4 or tetrachloromethane CCl4. Other combinations of substituents, such as a – b – c – d (but also a – b – c = d, or a = b – c = d, or a = b = c – d) give rise to structures that cannot be modeled as regular tetrahedra, since the bond lengths and bond angles in such molecules are nonequivalent. Despite this, only structures belonging to five symmetry point groups, Td, C3v, C2v, Cs, and C1, are possible, irrespective of whether Cabcd is modeled as a regular tetrahedron or as irregular tetrahedra having different, substituent-dependent bond lengths and bond angles. While the regular tetrahedron is the more straightforward model and is preferable for rationalizing stereochemistry at the undergraduate level for molecules containing stereogenic centers , it is important that both the instructor and students be fully aware that the tetrahedral model represents a simplification and that the use of irregular tetrahedra would be physically more realistic.
Keywords (Audience):
Second-Year UndergraduateKeywords (Domain):
Organic ChemistryKeywords (Subject):
Chirality / Optical ActivityCiting Articles
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This article has been cited by 3 ACS Journal articles (3 most recent appear below).
The Protocenter Concept: A Method for Teaching Stereochemistry
David E. LewisJournal of Chemical Education2010 87 (6), 604-607The Protocenter Concept: A Method for Teaching Stereochemistry
David E. LewisJournal of Chemical Education2010 87 (6), 604-607The protocenter, defined as an atom carrying two different attached groups in a nonlinear arrangement, is proposed as a concept useful for the introduction of chirality and geometric isomerism in introductory organic chemistry classes. Two protocenters ...
Stereogenic Centers and Axes: A Comparison of the Chiral Topologies Available to Cabcd and abC=C=Ccd
Paul Lloyd-Williams and Ernest GiraltJournal of Chemical Education2005 82 (7), 1031Stereogenic Centers and Axes: A Comparison of the Chiral Topologies Available to Cabcd and abC=C=Ccd
Paul Lloyd-Williams and Ernest GiraltJournal of Chemical Education2005 82 (7), 1031In this article we provide a comparative analysis of molecular chirality as a consequence of the presence of stereogenic centers and axes. We have found this to be a useful and informative classroom exercise that helps to put some of the most important ...
Chirality Made Simple: A 1- and 2-Dimensional Introduction to Stereochemistry
Robert E. GawleyJournal of Chemical Education2005 82 (7), 1009Chirality Made Simple: A 1- and 2-Dimensional Introduction to Stereochemistry
Robert E. GawleyJournal of Chemical Education2005 82 (7), 1009Using internal and external reflection elements in one-, two-, and three-dimensional space, the concept of chirality can be introduced in simple terms that are readily understood. Illustrations of 2-D chirality include block letters of the alphabet and ...
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- Received: August 03, 2009
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