Jacobsen Catalyst C344. Overview Asymmetric catalysis Lab overview Organometallic reactions Chiral GC analysis Optical Activity.

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Presentation transcript:

Jacobsen Catalyst C344

Overview Asymmetric catalysis Lab overview Organometallic reactions Chiral GC analysis Optical Activity

Asymmetric Catalysis

Asymmetric Synthesis Stereoselectivity Diastereomeric excess Enantiomeric excess From JOC, 2013, 78, % ee

Lab Overview

Lab 1 Formylation reaction Isolate chiral salt during reflux May not get to silica column of aldehyde

Lab 2 Imine formation Lowest yielding reaction Optical activity

Lab 3 Jacobsen’s catalyst Air, moisture stable! You do not need optical activity data

Lab 4 Finally getting to the point! Bleach: a green, stoichiometric catalyst Full characterization, with optical activity Submit sample for chiral GC Lab 5 can be used to catch up, finish characterization data

Organometallic Chemistry Mechanism: Wikipedia

Enantiomeric Excess Maybe due to radical mechanism Calculations of ee

Chiral GC Basics of separation Cyclodextrin column Calculating ee But which peak is which?

Optical Activity Chiral compounds bend plane polarized light Angle depends on concentration, path length, solvent, temperature, wavelength of light, which enantiomer Specific rotation [  ] 20 D = o (H 2 O) The specific rotation of sucrose is reported: D = sodium D-line = 589 nm

Calculation Specific rotation is calculated from observed rotation by [  ] =  / (c. l) – C (concentration) is in grams/mL – L (pathlength) is in decimeters Most samples are determined at more dilute concentrations (g/ 100mL) Dilution does affect rotation, so to compare to literature, you must obtain data at same concentration they did

Example Reported data: Compound A has a reported specific activity [  ] 23 D = 93 o (c = 1.9, CH 2 Cl 2 ) To repeat the experiment, you mixed 190 mg of compound in 10mL of methylene chloride at 23 o C and used a sodium lamp and standard tube. You obtained a rotation of 1.6 o What is the ee of your compound? – Answer: 90% ee (Mixture is 95% to 5%)