Organic Chemistry 1 · Stereocenters and configuration
Comparing two directions around a ring
Conditions: 1-Ethyl-1-methylcyclohexane, with no other substituents and no isotopic labels. Consider the carbon bearing ethyl and methyl.
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The question
Is that carbon an ordinary tetrahedral stereocenter?
Reveal the answer and explanation
Answer and explanation
Correct answer No; the two paths around the otherwise unsubstituted ring are equivalent.
Both ring ligands encounter the same sequence and reconnect equivalently.
Not this one Yes; clockwise and counterclockwise are intrinsically different chemical groups.
A drawing direction does not establish chemical distinguishability.
Not this one No; any carbon in a ring is forbidden from being stereogenic.
Unsymmetrical substitution can make the two ring paths distinct.
Worked solution
The center has methyl, ethyl, and two ring attachments. Starting along either ring direction gives equivalent carbon and hydrogen environments all the way around. Because those two ligands are identical, four distinguishable ligands are absent despite the different methyl and ethyl groups.
What you'll practice
Recognize identical cyclic ligands in an unsubstituted ring.
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