all configurations match after rotation
🪞ACS ORGANIC CHEMISTRY STUDY GUIDE
Stereochemistry and Conformations for the ACS Exam
Practice chirality, R and S labels, enantiomers, diastereomers, Newman projections, and cyclohexane chairs.
8 key ideas8 flashcards5 practice questions
Copy to my workspace →LISTEN WITH SOBATake this set with you.
Audio is saved on this device after the first play.
Reflection is only the first test.
every stereocenter is inverted
some, but not all, are inverted
Key ideas to know
Start with the relationships between ideas. Then close the notes and explain each one from memory.
- 01
Constitutional isomers differ in atom connectivity, while stereoisomers share connectivity and differ in spatial arrangement.
- 02
A tetrahedral stereocenter commonly has four different substituents.
- 03
Enantiomers are nonsuperimposable mirror images.
- 04
Diastereomers are stereoisomers that are not mirror images.
- 05
Cahn-Ingold-Prelog priority begins with atomic number at the first point of difference.
- 06
A meso compound contains stereocenters but is achiral because of internal symmetry.
- 07
Staggered conformations have lower torsional strain than eclipsed conformations.
- 08
In a cyclohexane chair, bulky groups usually prefer equatorial positions to reduce 1,3-diaxial interactions.
PART OF THE ACS ORGANIC CHEMISTRY GUIDE
See every set in this course and follow a focused review order.
Open the full ACS Organic Chemistry guide →Two ideas worth correcting now
NOT QUITE
→Clockwise always means R
USE THIS INSTEAD
That is true only when the lowest-priority group points away.
NOT QUITE
→A molecule with stereocenters must be chiral
USE THIS INSTEAD
A meso compound has stereocenters and is still achiral.
Flashcards
Answer before opening each card. The effort to retrieve is part of the learning.
1What makes two molecules enantiomers?Show answer ＋
They are nonsuperimposable mirror images.
2What makes two stereoisomers diastereomers?Show answer ＋
They are not mirror images of each other.
3How is priority assigned when directly attached atoms match?Show answer ＋
Compare the next set of attached atoms until the first difference appears.
4What happens to an R or S reading when the lowest-priority group points toward you?Show answer ＋
Invert the clockwise or counterclockwise result.
5What is a meso compound?Show answer ＋
An achiral compound with stereocenters and an internal symmetry element.
6Which Newman arrangement is lowest in energy for butane?Show answer ＋
The staggered anti arrangement with the methyl groups 180 degrees apart.
7What happens during a cyclohexane chair flip?Show answer ＋
Axial bonds become equatorial and equatorial bonds become axial, while up and down stay the same.
8Why does tert-butyl strongly prefer equatorial?Show answer ＋
Its size makes axial 1,3-diaxial interactions costly.
Explain it in your own words
Use the answer as a check after you have written or spoken your response.
01How can you tell whether two wedge-dash drawings show the same molecule?
Match connectivity, assign configurations, and account for allowed rotations before deciding.
02Why is a molecule with two stereocenters not guaranteed to have four stereoisomers?
Internal symmetry can produce a meso form and reduce the total count.
03How do you compare two chair conformations?
Count axial substituents and weight larger substituents more heavily.
04Why does rotating one bond not create a new configurational isomer?
Bond rotation creates conformers that interconvert without bond breaking.
05How does an SN2 reaction affect one reacting stereocenter?
Backside attack produces inversion at that carbon.
Related study materials
〜•‿•
Ready to remember this?
Copy the set and let Soba schedule what to review next.
Study this set for free →