Chem 51LB Week Summer Session 1 Kevin Chen

Lecture Outline Miscellaneous administrative stuff and friendly reminders Experiment #2: Nucleophilic substitution (Part 2 of 2) Experiment #3: Stereochemistry of bromine addition to alkene

Lecture and lab participation Dr. Borovik’s unique participation method… clapping

Lecture and lab participation Dr. Borovik’s unique participation method… clapping Who wants to get an A in this class?

Lecture and lab participation Dr. Borovik’s unique participation method… clapping Who wants to get an A in this class? Who will obey all safety rules in lab?

Lecture and lab participation Dr. Borovik’s unique participation method… clapping Who wants to get an A in this class? Who will obey all safety rules in lab? Who will write great lab reports and learn a lot and make me proud?

Safety reminder (part 1) Proper glove usage – Do not touch your phone, computer, face, door knobs, etc with gloves on. – Place plastic wraps to cover your electronic devices – Remove glove before leaving lab – Change gloves when you think they are dirty  to avoid contamination WASH HANDS BEFORE LEAVING LAB!

Safety reminder (part 2) Proper PPE – Shirt with sleeves, long pants, close-toe shoes, goggles (not glasses), and lab apron Proper waste disposal – Glass waste in regular trash = major no no – Chemical waste in trash or sink = major no no CONSEQUENCES – lose TA discretion points – Get kick out of lab (lose lots of points) – EVERYONE in the ENTIRE section drops a grade!

Proper TLC disposal Regular trash Specialized container

What to do with used TLC plates Regular trash Specialized container

Dr. Link’s videos The videos will explain theoretical concepts of lab techniques, experiments, data analysis, etc. They are great! Watch them!

Be prepared! People are unprepared  work slower Exactly 4 hrs to perform lab AND clean up – No exception! – Lose major TA discretion points – Lose points related to the incomplete data – Get on TA’s and stockroom’s bad side Solution: BE PREPARED!

Report scaffolds reminder Answer all questions – Understand why those questions were asked Answer in full sentences or paragraphs – Exception: some data can be in tables for results Understand when it is a good time to use tables AND what information should be included ALWAYS include unknown number Make grading easy for grader aka your awesome TAs

Experiment #2 Nucleophilic substitution (Part 2 of 2) Given: your own material from part 1 Goal: recrystallization of crude product, mix melting point and TLC End game: Identify your unknown through the analysis of your product with MP, TLC, AND NMR

Recrystallization A great way for “painless” purification of crude product containing product, starting material, byproducts, etc. Often require two solvents, a good and a bad one – Good solvent (dissolves material) – Bad solvent (crashes out material) Patience is a virtue! DO NOT ADD TOO MUCH OF THE GOOD SOLVENT!

Mix melting point A great way to confirm that your recrystallized product is pure (or more pure than before) Your product + standard (pure compound that stockroom provided) should have same melting point range as MP of just the standard, WHY?

Mix melting point A great way to confirm that your recrystallized product is pure (or more pure than before) Your product + standard (pure compound that stockroom provided) should have same melting point range as MP of just the standard, WHY? They are the same material! What happen if your product is not pure?

Mix melting point A great way to confirm that your recrystallized product is pure (or more pure than before) Your product + standard (pure compound that stockroom provided) should have same melting point range as MP of just the standard, WHY? They are the same material! What happen if your product is not pure? MP depreciation, but hopefully not as much as before recrystallization

Thin Layer Chromatography (TLC) One of the most important lab technique in organic chemistry Separate organic compounds based on their polarity By The original uploader was Natrij at English Wikipedia - Transferred from en.wikipedia to Commons., CC BY-SA 3.0,

Thin Layer Chromatography (TLC) One of the most important lab technique in organic chemistry Separate organic compounds based on its polarity By The original uploader was Natrij at English Wikipedia - Transferred from en.wikipedia to Commons., CC BY-SA 3.0, How many compounds are in black ink?

Thin Layer Chromatography (TLC) One of the most important lab technique in organic chemistry Separate organic compounds based on its polarity By The original uploader was Natrij at English Wikipedia - Transferred from en.wikipedia to Commons., CC BY-SA 3.0,

TLC background Stationary phase (solid)  usually silica, which is a silicon based material that is polar Mobile phase (liquid)  usually a solvent mixture of two organic solvent, one polar and one “relatively” nonpolar The mobile phase is relatively nonpolar compared to the stationary phase – This difference in polarity means organic compounds either likes to interact with polar stationary phase or nonpolar mobile phase

Mobile phase matters A LOT Relative polarity differences between compounds A, B, and C is the same

Monitoring reaction Rf value = retardation factor Rf = distance to spot/ distance to top (unitless!)

Common TLC problems I cannot see my spots! – Not UV active  stain it – Not enough material  spot more material My spots are streaking! – Too much material  spot less material next time My spots/lanes are going sideways! – TLC was places diagonally into the TLC chamber  use a tweezer and place TLC plate in slowly

Experiment #3: Stereochemistry of bromine addition to alkene Product analysis can help elucidate rxn mechanism (syn vs anti vs racemic) Goal: Conduct bromination rxn, workup (quench), vacuum filtration, recrystallization, and MP End game: Determine if the brominated alkene is syn or anti or racemic

Data analysis Syn products are enantiomers (R,R and S,S) Anti products are enantiomers (R,S and S,R) Syn and Anti are diastereomers Enantiomers have the same chemical properties except optical rotation Diastereomers have different chemical properties If you have enantiomers, can you tell which one you have?

Next week July 4 th (Monday) – No lab lecture – No lab – No office hour July 5 th (Tuesday) – No lab – Office hour July 6 th and 7 th (Wednesday and Thursday) – Acid/base separation