Uploaded February 2026 | Updated September 2026, 1 week ago
Most students get the math right for enantiomeric excess (ee), but they can still get the exam question wrong. Why? Because they stop too early.
In this video, we go beyond the basic formulas to look at the logic of optical rotation. Whether you're working with polarimeter data, observed rotation, or racemic mixtures, there's a specific "missing step" you need to master to actually identify the percentages of dextrorotatory and levorotatory enantiomers in a sample.
Instead of just memorizing the equation, we're going to build a mental map of how chiral molecules interact with light so you can troubleshoot your own lab data and exam answers.
What we'll solve together:
• How to interpret polarimeter data without getting confused by units
• The real difference between dextrorotatory (+) and levorotatory (-)
• The "not done" trap: How to turn an ee percentage into a full enantiomeric breakdown (Watch at 15:50)
• How to check your work to guarantee 100% accuracy
Related Units:
🧪 Part of the Organic Chemistry Chirality Series: youtube.com/playlist?list=PLvUW25kBaMMupOdw1Wgy8YauiQ40J_5nx
For organic chemistry reaction mechanisms, watch this: youtube.com/playlist?list=PLvUW25kBaMMtvqt_IBtezyBX_kk447pxZ
For all of my ochem videos in one place: youtube.com/playlist?list=PLvUW25kBaMMuKRkW9gDV7vlAk4Y9WRU7c
If you need to take the MCAT: youtube.com/playlist?list=PLvUW25kBaMMuJZI5IVWO8X0syBANn-YqY
🧪Support free education & more through Patreon! patreon.com/c/ChemistryinaNutshell
🥽As an Amazon Affiliate, I earn from qualifying purchases at no extra cost to you.
🥼Need a molecular model kit or other chem supplies? amazon.com/shop/chemnut?ccs_id=11f20bce-5f74-427b-85fb-bdf66849405a
🔬Start any shopping journey here: amzn.to/3IXuAcS
Images:
"Low Pressure Sodium Lamp" By Proton02 - Own work, Public Domain, commons.wikimedia.org/w/index.php?curid=1678845
"Project 365 #21: 210111 Sodium Halo" by comedy_nose is marked with Public Domain Mark 1.0. To view the terms, visit creativecommons.org/publicdomain/mark/1.0/?ref=openverse.
"Fireworks, Greenwich Tall Ships Festival" by barry.marsh1944 is marked with Public Domain Mark 1.0. To view the terms, visit creativecommons.org/publicdomain/mark/1.0/?ref=openverse.
Citations:
Paula Yurkanis Bruice, "Organic Chemistry" 8th ed
openstax.org/details/books/organic-chemistry
openstax.org/details/books/chemistry-2e
Music: youtu.be/lL6AsbG07xY
0:00 Intro
0:12 Polarimeter Demo
1:02 589 nm Sodium Arc Lamp
1:44 Observed Rotation & Path Length
2:26 Chiral Molecules, Dextrorotatory, Levorotatory
3:30 Racemic Mixtures
4:34 Terminology & Variables
8:01 Specific Rotation Equation
8:55 Enantiomeric Excess Equations
10:09 Observed Rotation Calculation
13:24 Dextrorotatory or Levorotatory?
13:46 Enantiomeric Excess Calculation
15:50 Where Most People Mess Up! (40% isn't the answer)
18:22 Check Your Work on EE Calcs!
Most students get the math right for enantiomeric excess (ee), but they can still get the exam question wrong. Why? Because they stop too early.
In this video, we go beyond the basic formulas to look at the logic of optical rotation. Whether you're working with polarimeter data, observed rotation, or racemic mixtures, there's a specific "missing step" you need to master to actually identify the percentages of dextrorotatory and levorotatory enantiomers in a sample.
Instead of just memorizing the equation, we're going to build a mental map of how chiral molecules interact with light so you can troubleshoot your own lab data and exam answers.
What we'll solve together:
• How to interpret polarimeter data without getting confused by units
• The real difference between dextrorotatory (+) and levorotatory (-)
• The "not done" trap: How to turn an ee percentage into a full enantiomeric breakdown (Watch at 15:50)
• How to check your work to guarantee 100% accuracy
Related Units:
🧪 Part of the Organic Chemistry Chirality Series: youtube.com/playlist?list=PLvUW25kBaMMupOdw1Wgy8YauiQ40J_5nx
For organic chemistry reaction mechanisms, watch this: youtube.com/playlist?list=PLvUW25kBaMMtvqt_IBtezyBX_kk447pxZ
For all of my ochem videos in one place: youtube.com/playlist?list=PLvUW25kBaMMuKRkW9gDV7vlAk4Y9WRU7c
If you need to take the MCAT: youtube.com/playlist?list=PLvUW25kBaMMuJZI5IVWO8X0syBANn-YqY
🧪Support free education & more through Patreon! patreon.com/c/ChemistryinaNutshell
🥽As an Amazon Affiliate, I earn from qualifying purchases at no extra cost to you.
🥼Need a molecular model kit or other chem supplies? amazon.com/shop/chemnut?ccs_id=11f20bce-5f74-427b-85fb-bdf66849405a
🔬Start any shopping journey here: amzn.to/3IXuAcS
Images:
"Low Pressure Sodium Lamp" By Proton02 - Own work, Public Domain, commons.wikimedia.org/w/index.php?curid=1678845
"Project 365 #21: 210111 Sodium Halo" by comedy_nose is marked with Public Domain Mark 1.0. To view the terms, visit creativecommons.org/publicdomain/mark/1.0/?ref=openverse.
"Fireworks, Greenwich Tall Ships Festival" by barry.marsh1944 is marked with Public Domain Mark 1.0. To view the terms, visit creativecommons.org/publicdomain/mark/1.0/?ref=openverse.
Citations:
Paula Yurkanis Bruice, "Organic Chemistry" 8th ed
openstax.org/details/books/organic-chemistry
openstax.org/details/books/chemistry-2e
Music: youtu.be/lL6AsbG07xY
0:00 Intro
0:12 Polarimeter Demo
1:02 589 nm Sodium Arc Lamp
1:44 Observed Rotation & Path Length
2:26 Chiral Molecules, Dextrorotatory, Levorotatory
3:30 Racemic Mixtures
4:34 Terminology & Variables
8:01 Specific Rotation Equation
8:55 Enantiomeric Excess Equations
10:09 Observed Rotation Calculation
13:24 Dextrorotatory or Levorotatory?
13:46 Enantiomeric Excess Calculation
15:50 Where Most People Mess Up! (40% isn't the answer)
18:22 Check Your Work on EE Calcs!
