SYNT 721. A Wittig Reaction CHEM 3780

Experimental Notes: 1. Please read and be familiar with the background (p. 209-211) and semi-microscale procedure (p. 212-215, 217-219) before

coming to lab. (75 pts) Lab Write-up: (1pts) Date and Title of Experiment (1 pts) Objective (5 pts) Reaction Scheme with balanced equation— (i) include the mechanism beginning with PhCH2PPh3Cl and NaOH

to form the ylide; and (ii) label the betaine and oxaphosphatene intermediates. (4 pts) Table of physical constants for each reactant and product. Include hazards associated with use of each. (4 pts) Outline of procedure. ************************************************************************************************** (25 pts) Observations and calculations (data recorded during the lab)

1. (10 pts) Include observations that you make during the experiment. 2. (10 pts) Show the calculation of the theoretical yield and percent yield of your Wittig product. 3. Recrystallize your product from 2-propanol, and obtain a TLC and IR of your recrystallized product. 4. (5 pts) Sketch your TLC plate in your notebook; calculate the Rf of your product and starting material. 5. Determine the melting point of your dried product.

(25 pts) Results and Discussion 1. (5 pts) Using the melting point and IR data from your compound, what evidence allows you to conclude

that your product is trans-9-(2-phenylethenyl)anthracene? 2. (5 pts) Prepare a table showing all the pertinent absorption in the IR spectrum and their assignment. 3. (5 pts) Using the 1H NMR, identify the double bond 1H peaks (note the chemical shift) and calculate the

coupling constant. What evidence supports the synthesis of the trans-isomer instead of the cis-isomer? 4. (5 pts) What combination of carbonyl and phosphorous ylide could you use to synthesize the following?

CH3CH2CH(CH3)CH=CHCH3 (CH3)2C=CHC6H5

(10 pts) Conclusions Hint for determining the coupling constant

1. Identify the two olefin hydrogens—they should have identical coupling constants and will integrate to 1 H each.

2. Determine the coupling constant (J) in millimeters (x mm). 3. Determine how many mm are in 1 ppm (y mm). Then, assume that

1 ppm = 400 Hz = y mm. 4. Set up a ratio and solve for J. This is the coupling constant between

the olefin hydrogens.

x mm

J=

y mm

400 MHz