Nucleophilic+Substituion+Reaction

**Background Information:**
Whether a substitution reaction decides to proceed in a Sn1 or Sn2 manner depends on the solvent the reaction takes place in, the alkyl halide (leaving group), and the characteristics of the nucleophile, and the structure of the Carbon structure at hand. This experiment shows how reaction time is affected with each change in solvent and alkyl halide.

**Introduction:**
This experiment investigates what effect the solvent will have between 2-chloro-2-methyl propane and water. The Sn1 reaction between 2-chloro-2-methyl propane and water is as follows:

2-Chloro-2-methyl propane + water >>>>>> (R/S) 2-methyl-2- hydroxypropane + protonated hydrogen

For additional "Style" points, include the reaction drawn out, and/or provide additional explanation of what the theory is behind the polar protic/polar aprotic and SN1 reaction trends we expect. Tell me what you expect to see--a sort of hypothesis.

**Procedure**:
This procedure comes from Ken Doxsee and Jen Hutchinson's laboratory text, "Green Organic Chemistry, Strategies, Tools, and Laboratory Experiments."

To begin, collect the materials to set up the apparatus: 5 - 25mL Erlenmeyer Flasks, a stir bar, magnetic stirrer, 2-3 graduated glass pipets, a stopwatch, and 5 small test tubes. First, label the five test tubes A-E, and the five flasks #1-5. Using the glass pipets, add 2.0 mL of 0.1 M alkyl halide into the first four test tubes (A-D). With test tube E, add 2.0mL of 0.1M HCL with the glass pipet. Next, begin to fill each Erlenmeyer flask with the directed amount of water, 0.01M NaOH, color indicator, and Acetone or Isopropanol as assigned. Use the table for clear guidance:

(as assigned) || 3.0mL || 3.0mL || 2.0mL || 1.0mL || none || Once this is completed, the experiment is ready to begin. Start by putting the stir bar into Flask #1 and onto the magnetic stirrer. Get the stop watch ready, and pour the contents of test tube E into Flask #1 and begin timing, in seconds. Record the number of seconds it took for the solution to change colors. Record this on a chart. Repeat this procedure for the remaining four test tubes and flasks. Test Tube A for Flask #2, B for #3, C for #4, and D for #5.
 * **Material** || **Flas**k #1 || **Flask #2** || **Flask #3** || **Flask #4** || **Flask #5** ||
 * Water || 3.0mL || 3.0mL || 4.0mL || 5.0mL || 6.0mL ||
 * 0.01 M NaOH || 2.0mL || 2.0mL || 2.0mL || 2.0mL || 2.0mL ||
 * Acetone/Propanol
 * Indicator || 3 drops || 3 drops || 3 drops || 3 drops || 3 drops ||

Calculate the percent composition of water in each flask after adding the alkyl halide and record these values in Table #2 in the procedure. Also, complete the table to show the concentration of NaOH in M in each flask after the addition of HCl and RCl as well as the concentration of HCL (Flask #1) and RCl (Flasks #2-5).

Data/Results: Our data using iPA as a solvent: Other data from another group using Acetone as a solvent:
 * **Material** || **Flask #1** || **Flask #2** || **Flask #3** || **Flask #4** || **Flask #5** ||
 * **% Water** || 30% || 30% || 40% || 50% || 60% ||
 * **[NaOH]** || 0.002M || 0.002M || 0.002M || 0.002M || 0.002M ||
 * **[HCl]** || 0.02M || None || None || None || None ||
 * **[RCl]** || None || 0.02M || 0.02M || 0.02M || 0.02M ||
 * **Flask #1** || **Flask #2** || **Flask #3** || **Flask #4** || **Flask #5** ||
 * 0.41 sec || 693 sec || 464 sec || 106 sec || 16.5 sec ||
 * **Flask #1** || **Flask #2** || **Flask #3** || **Flask #4** || **Flask #5** ||
 * 2.00 sec || 700 sec || 213 sec || 56.0 sec || 18.0 sec ||

For additional points in this category, take the time to graph out the results. The trends will become very clear when you look at the data in that form.

Conclusion:
Looking at the results from the lab, it can be deduced that the smaller amount of acetone or propanol used as well as the more water, the faster the reaction rate was. The results suggest that the use of acetone created faster reaction times than the use of propanol. This is a troubling result considering the polarity of the different reactions. Polan solvents lower the potential energy of the reactants and therefore quicken the reaction rate. Water is a polar solvent in this reaction, and the more water that was used, the faster the reaction rate was. yes, good.... Both acetone and propanol were not nearly as polar as water, but propanol is more polar than acetone. actually it is NOT! It is protic, and as an alcohol you might think it more polar, but it is not. This is why are results do not represent what should have happened well. The reactions should happen quicker with polar solvents. The reactions in flasks containing acetone should have lasted longer than those with propanol, so errors in the lab must have led to these skewed reaction times. At least the amount of water used in each flask and reaction times were consistent. These trends were very consistent across groups and in both sections of lab. I think they're for real.

If you look up each solvent (acetone and isopropranol) on Wikipedia, you can find the dipole moment. You'll discover that acetone is actually quite a bit more polar than iPA.

Errors:
Some of our flasks did not have a designated blue tint to them before commencing the reaction, so a few more drops of the indicator were added. This could have affected the percent of each reactant in those flasks, but I do not think it would have affected the times recorded very much. Also, some of the lab groups could have forgotten to wash pipets out before using them again, which would indeed alter results since the amounts of each solvent and reactant added were to be very precise. Poor or sloppy measurements could also be a reason for the poor results. I'm in complete agreement on your first two potential errors. As for the third one--remember that preventable errors (sloppy measurement, inaccurate records, etc.) are not excusable and therefore we should not expect them to be (very) influential.