CHE 230-002

Facts and Skills to Master for the Second Exam

The second exam will cover Chapters 1–5 in Klein. The following guidelines are not meant to be complete or comprehensive lists of the information you are expected to know.

You are expected to have command of all the material covered on the first exam.

You should be able to determine whether a structure X–C–C–Y is in an eclipsed or staggered conformation, and, if the latter, you should be able to determine whether X and Y are anti or gauche. You should be able to calculate the difference in energy between different conformations of a compound, and you should be able to draw a graph of energy vs. dihedral angle about a C–C bond.

Given its name, you should be able to draw a substituted cyclohexane in either chair conformation, and you should be able to determine which conformer is higher in energy. Given a table of energies of 1,3-diaxial interactions, you should be able to determine the difference in energy between two chairs.

You should be able to determine whether a structure, possibly a cyclohexane, is chiral or achiral by looking at its symmetry or its stereocenters. You should also be able to determine whether a compound, possibly a cyclohexane, is chiral or achiral overall (depending on whether it has at least one achiral conformation).

You should be able to determine whether two structures, possibly cyclohexanes or alkenes, are:

• skeletal isomers;
• configurational diastereomers;
• configurational enantiomers;
• conformational diastereomers;
• conformational enantiomers;
• resonance structures; or,
• identical (homomers).

You should be able to draw one or more stereoisomers of a structure or a compound, including an alkene.

You should be able to identify the sp³ stereocenters in a compound.

You should understand why and under what circumstances alkenes can have diastereomers, and you should be be able to determine whether a particular alkene has a diastereomer.

You should be able to use the mathematical relationship between the ee of a compound, its observed optical rotation, and its specific rotation to calculate any one of these values, based on the other two. You should be able to interconvert the ee and the enantiomeric ratio (er) of a compound.

You should understand the following concepts and be able to use them logically:

• In a chemical reaction, optically inactive starting materials (achiral, or chiral and racemic) give optically inactive products.
• Two enantiomers have the same physical properties (except for optical activity), whereas two diastereomers have different physical properties.
• Although two enantiomers have identical interactions with achiral substances, their interactions with chiral substances, such as living organisms, can differ.
• Two enantiomers can be separated by the process of resolution, which involves a reaction with a chiral, enantiopure reagent.
• In asymmetric synthesis, at least one optically active (chiral and enantioenriched) starting material or reagent, possibly along with other optically inactive (achiral, or chiral and racemic) starting materials or reagents, is used to prepare an enantioenriched product.

You may find these handouts helpful.

Return to the Grossman CHE 230 page.

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