CHEM 281 Chapter Notes - Chapter 3: Alkane Stereochemistry, Substituent, Methyl Group
30 Aug 2018
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Chapter 3 notes part 17: an introduction to organic compounds. Unlike cyclohexane, which has two equivalent chair conformers, the two chair conformers of a monosubstituted cyclohexane (such as methylcyclohexane) are not equivalent. The chair conformer with the methyl substituent in an equatorial position is the more stable of the two conformers because a substituent has more room and, therefore, fewer steric interactions when it is in an equatorial position. This can be understood by looking at figure 3. 14a, which shows that a methyl group in an equatorial position extends into space, away from the rest of the molecule. In contrast, any axial substituent will be relatively close to the axial substituents on the other two carbons on the same side of the ring because all three axial bonds are parallel to each other (figure 3. 14b). Because the interacting axial substituents are in 1,3-positions relative to each other, these unfavorable steric interactions are called 1,3-diaxial interactions.
