Organic Structure & Stereochemistry

Each list begins with basic conceptual vocabulary you need to know for MCAT questions and proceeds to advanced terms that might appear in context in MCAT passages. The terms are links to Wikipedia articles.
Stereochemistry involves the study of the relative spatial arrangement of atoms within molecules.
The term chiral is used to describe an object that is non-superimposable on its mirror image.
Cis-trans isomerism
Cis-trans isomerism is a form of stereoisomerism describing the orientation of functional groups typically around double bonds which cannot rotate.
Steric effects
Steric effects arise from the fact that if atoms are brought too close together, there is an associated cost in energy due to overlapping electron clouds.
Enantiomers are stereoisomers that are nonsuperimposable complete mirror images of each other.
A racemic mixture is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule.
Diastereomers are stereoisomers that are not enantiomers.
Optical activity
Optical rotation or optical activity is the rotation of linearly polarized light as it travels through certain materials.
Meso compound
A meso compound is a chemical compound with molecules that contain 2 or more stereocenters but which is optically achiral because it contains an internal plane of symmetry.
Newman projection
A Newman projection visualizes chemical conformations of a carbon-carbon chemical bond from front to back, with the front carbon represented by a dot and the back carbon as a circle.
Staggered conformation
A staggered conformation is a chemical conformation that exists in any open chain single chemical bond connecting two sp3 hybridised atoms as a conformational energy minimum.
Eclipsed conformation
An eclipsed conformation is a chemical conformation that exists in any open chain single chemical bond connecting two sp3 hybridised atoms as a conformational energy maximum.
A stereocenter is any atom in a molecule bearing groups such that an interchanging of any two groups leads to a stereoisomer.
Conformational isomerism
Conformational isomerism is a form of stereoisomerism involving molecules with the same structural formula existing as different conformers due to atoms rotating about a bond.
Van der Waals strain
Van der Waals strain results from van der Waals repulsion when two substituents in a molecule approach each other with a distance less than the sum of their van der Waals radii.
Cyclohexane is a cycloalkane containing 6 carbons and 12 hydrogens, which has the lowest angle and torsional strain of all the cycloalkanes.
Angle strain
The presence of angle strain in a molecule indicates that in a specific chemical conformation bond angles are deviating from the ideal bond angles required to achieve maximum bond strength.
Ring strain
Ring strain is an organic chemistry term that describes the destabilization of a cyclic molecule-such as a cycloalkane-due to the non-favorable high energy spatial orientations of its atoms.
Chiral resolution
Chiral resolution in stereochemistry is a process for the separation of racemic compounds into their enantiomers.
Prochiral molecules can be converted from achiral to chiral in a single step.
Hyperconjugation is the stabilizing interaction that results from the interaction of the electrons in a sigma bond with an adjacent empty or partially filled non-bonding p-orbital or antibonding pi orbital leading to an extended molecular orbital that increases the stability of the system.
Anomeric effect
The anomeric effect or Edward-Lemieux effect describes the tendency of heteroatomic substituents adjacent to a heteroatom within a cyclohexane ring to prefer the axial orientation instead of the expected, less-hindered equatorial orientation.
Enantiomeric excess
Enantiomeric excess exists where one enantiomer is present more than the other in a chemical substance.
Baeyer strain theory
Baeyer strain theory explains specific behaviour of chemical compounds in terms of bond angle strain.
Enantiomer self-disproportionation
Enantiomer self-disproportionation is a process describing the separation of a non-racemic mixture of enantiomers in an enantioenriched fraction and a more racemic fraction.
Homochirality is a term used to refer to a group of molecules that possess the same sense of chirality with similar groups are arranged in the same way around a central atom.
Chiral pool synthesis
Chiral pool synthesis is a strategy that aims to improve the efficiency of chiral synthesis by beginning from a stock of readily available enantiopure substances.
Asymmetric induction
Asymmetric induction describes the preferential formation in a chemical reaction of one enantiomer or diastereoisomer over the other as a result of the influence of a chiral feature present in the substrate, reagent, catalyst or environment.
Chiral auxiliary
A chiral auxiliary is a chemical compound or unit that is temporarily incorporated into an organic synthesis so that it can be carried out asymmetrically with the selective formation of one of two enantiomers.
Circular dichroism
Circular dichroism is a form of spectroscopy based on the differential absorption of left- and right-handed circularly polarized light.

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