Intro-to-Nucleophilic-Substitution

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Iowa State University *

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331L

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Chemistry

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Dec 6, 2023

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pdf

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6

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TEMPLATE: 331L Intro to Nucleophilic Substitution Name: Kim Huynh Section: TA First Name: TA email: Combination: Pre-lab Questions Reminders: All work must be legible or it will not be graded. Do not copy and paste structures or mechanisms unless instructed to do so. 1. Read the Safety and Procedure for this experiment. a. (10 pts) Write a bullet list outline for the procedure. Weigh a 50mL Erlenmeyer flask. Add 2,5-dimethyl-2,5-hexaniediol into flask Add HCl to a flask, stir 5-10 min by a stir bar Add 10mL hexane and put in centrifuge tube Invert and vent, then layers to separate Remove the organic layer and transfer to 125 mL Erlenmeyer flask Transfer the organic layer to rotovap flask and repeat extraction once more Give flask to TA for rotovating Use TLC plate with 10 mL of 95% hexanes/5% ethyl acetate Dip TLC paper in PMA stain Take to TA to heat by hot gun Take photo and calculate Rf Determine the melting point of the product Obtain the IR spectrum of the product b. (5 pts) Write a brief summ ary of the key safety concerns specific for this experiment.  The chemicals used in this lab are very toxic, flammable, irritating, and highly corrosive ; so they must be handled carefully, carefully change new gloves when these chemicals come to contact your gloves. 2,5- Dimethyl-2,5-hexanediol is causes serious eye damage, must wear safety goggles, if it comes to contact eyes, must call for help and wash eyes with cool water. And all containers containing these substances must be closed to avoid causing danger. 2. (15 pts) Label the substrate, leaving group and nucleophile in the reaction scheme below. 3. (10 pts) Carbocation stability is important to examine when determining whether a substitution is S N 2 or S N 1. Look at the reaction scheme above. Is the substrate a 1 o , 2 o , or 3 o carbon? Does this type of carbon form a stable carbocation? The substrate is a 3 o carbon. Yes, it forms a stable carbocation. 4. (10 pts) Based on what you learned from the tutorials on C anvas for today’s experiment, which substitution mechanism do you predict for the substitution reaction involving 2,5-dimethyl-2,5- hexanediol and HCl? Explain briefly why you chose this mechanism.
The substrate carbon is 3 o carbon, forms a stable carbocation; the reaction takes over one step, so it is not SN2. It is SN1 reaction. 5. (35 pts) Draw todays synthesis using the reaction mechanism you chose in question 4. 6. (15 pts) calculate how much substrate and reagent to use based on moles. The following table guides you in this calculation. Amounts to Use for Reaction Reactant Reactant 2,5-dimethyl-2,5- hexanediol Conc HCl (aq) Moles 7 mmol 15x excess = 15 * 7 mmol = 105 mmol MW 146.23 g/mol NA Concentration NA 11.65 M (or mmol/mL) Amount Calculate and write in pre- lab notes. T Be sure and record exact amount Calculate and write in pre-lab notes. In-lab Notes 2,5-dimethyl-2,5-hexanediol: mass= moles x MW= 7/1000 mol x 146.23g/mol= 1.024 (g) Volume of HCl V = 105 mmol ÷ 11.65 mmol/mL = 9.012 (ml) In-lab Notes Erlenmeyer Flask 50mL: 41.223g Erlenmeyer Flask 50mL + 2,5 Dimethyl-2,5 hexanediol: 42.244g 2,5 Dimethyl-2,5 hexanediol: 1.021g HCL: ~9 mL Mass of 100ml rotovap flask: 75.581g Mass of 100ml rotovap flask+ product: 76.531g 18mg for NMR sample. Fumehood 25 for proton NMR Melting point 65 o C -69 o C.
TLC plate: - Solvent front: 6.3cm. - Crude product distance 5.4 cm. - Reactant distance: 0 cm Analysis and Application Questions Do not copy and paste structures or mechanisms from any source. Answers must be legible or they will not be graded. Data and Observations 1. (7 pts) Include a photo of your TLC plate showing product purity. Calculate the R f value for each spot (compound) on your TLC plate. 2. (8 pts) Calculate the percent yield. Show your calculations in order to get credit. From the reaction, 2,5-dimethyl-2,5-hexanediol is limited reactant, so the product 2,5-dichloro- 2,5- dimethylhexane is 7 mmol. Theorical mass of product: 7/1000 mol x 183.12 g/mol = 1.282 (g)
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