The purpose of this experiment is to compare the relative nucleophilicities of chloride ions and bromide ions towards a primary alcohol and a tertiary alcohol. In part A, the primary alcohol, 1-butanol (omit the 2-butanol) yields a mixture of 1-chlorobutane and 1-bromobutane. In Part B, the tertiary alcohol, 2-methyl-2-propanol yields a mixture of 2-bromo-2-methylpropane + 2-chloro-2-methylpropane. These products have been analyzed by Gas Chromatograph and give the attached chromatograms, labeled Part A and Part B. You can see that the ratio of products differs when comparing Part A to Part B reactions and this difference is due to several factors, including the strength of the nucleophile and whether the mechanism of the reaction is SN1 or SN2 (see conclusion section of lab report template for more information).
The first thing you must do is triangulate the areas of the 2 peaks in each part to approximate their mole %. This technique is demonstrated in the Techniques section of your lab manual under Gas Chromatography (the actual page for the technique is given in the lab procedure in the Part C Analysis section of the procedure; for the 3rd ed. it's on page 722 - 723). Here's how I would do it (a little different from the book, but you can triangulate either way):
For Part A: Visualize each peak as a triangle. Using a ruler, measure the height of the first peak. Then measure the base of the peak (bottom of the triangle) from where the peak begins to leave the baseline to where it meets the baseline again. Calculate the area of the peak by using the equation for the area of a triangle: 1/2 Base x Height. Repeat this measurement on the next peak to determine the area of the second peak. Now you have the area of both peaks. To determine "mole %" you will add the areas of both peaks together to get the sum of the peaks, then determine the % of each peak as follows: (area of 1st peak / sum of peaks) x 100, then (area of 2nd peak / sum of peaks) x 100.
Repeat this process for Part B (see lab report template). To complete the lab, you must determine if Part A products are formed by an SN1 or SN2 reaction and why, then do the same for Part B. Refer to the conclusion section of the lab report. Also answer questions 2,4, & 7. I strongly suggest you read the section in your lecture text on characteristics of SN1 and SN2 reactions if you want to succeed with this analysis. Also, on the lab report template, you must replace all of the blue lettering in the purpose, reaction, and procedure, so don't lose points due to carelessness!
This report may take a bit more work than others you've done, so please don't wait until the last minute to work on it. Feel free to email any questions you have, but only after you've carefully read the entire procedure, techniques section for Gas Chromatography and corresponding sections on nucleophilic substitution reactions in your lecture text. I think once you've done this research, you'll be able to answer your own questions.
|Due By (Pacific Time)
||12/14/2014 02:00 pm