Nucleophilic Substitution

Topics: Chemical kinetics, Reaction rate constant, Chemistry Pages: 5 (1392 words) Published: May 26, 2014


CHEM/ENCH 212

EXPERIMENT II: KINETICS OF NUCLEOPHILIC SUBSTITUTION

DATE OF SUBMISSION:
Table of Contents

Experimental

Table : Hazardous properties of chemicals used in the experiment.[1] Acetone
Irritant. Do not inhale vapors. Highly flammable.
2 chloro, 2 methyl propane
Flammable.

Equipment
1. Conductivity probe
2. Constant temperature water circulation bath
3. Stir-plate with stirring magnets
4. 20 mL vials
5. Eppendorf pipette
6. Computer with LoggerPro

Procedure
For the fully detailed procedure, please refer to the CHEM/ENCH 212 Laboratory Manual.[2]

10 mL of a provided 85/15 water/acetone mixture was taken in a vial and placed in a constant temperature water circulation bath set to approximately 35°C. A calibrated conductivity probe was added to the solution, along with a magnetic stirrer. After this, 200 μL of 2-chloro, 2-methylpropane (also called t-butyl chloride) solution was added using a pipette and data for the change in conductivity with respect to time was found.

This experiment was then repeated several times, changing a variable on each occasion: 1. Original run, 10 mL of 85/15 acetone solution, 200 μL of 2-chloro, 2-methylpropane. 2. Same as original, but with 400 μL of t-butyl chloride.

3. Same as original but with 800 μL of t-butyl chloride.
4. Same as original but with 90/10 water acetone solution.
5. Same as original but with 80/20 water acetone solution.
6. Same as original, but with the water bath at 45°C.
7. Same as original, but with no water bath (room temperature run).

One change made to experimental procedure was that for the sixth run, instead of setting the water bath to 45°C, it was set to 48.5°C, since the temperature being used was an approximation, and it would have wasted time to try to set the temperature to exactly 45°C. The other was that the conductivity probe was tapped after it was placed in the solution, so as to remove any air bubbles, which would affect the readings.

Results

PART A

Figure : Graph showing the variation of conductivity with time for different amount of t-butyl chloride.

Figure : A graph showing the rate reaction constant for each trial, using a line of best fit for a limited, linear section of each trial.

Figure : A plot showing the three rate constants obtained from the different trials. Figure 3 clearly indicates that for first-order reaction systems, the k-value is dependent of the initial reactant concentration. The graph illustrates that increasing the initial amount of reagent added, decreases the k-value. In addition to this, theoretically the k-value is supposed to be dependent of the initial concentration for first order reactions.[4]

PART B

Figure : A graph depicted how the conductivity varied with time for different percentage compositions of the acetone/water solution.

Figure : Linearized data traces for the three trials with different acetone percentages.

Figure : Comparison of the k-values obtained for the corresponding different percentages of acetone for each trial.

The trend observed from the Figure 6 shows, that as you decrease the percentage of acetone in the mixture, greater the reaction rate constant becomes. The graph clearly shows that the reaction mechanism is SN1 because SN1 reactions use polar solvents to stabilize the respective carbocation, therefore as the percentage of water used was increased, the reaction rate constant increased.[5]

PART C

Figure : A plot showing how different temperature trials produced varying results for the conductivity over time.

Figure : Linearized data traces for the three different temperature trials.

Figure : A plot using the ln(k) values and the inverse of the temperature to give a relation for the Arrhenius data. The Arrhenius plot shows a linear relationship for our reaction system. This...


Cited: 1. Sigma-Aldrich Co. LLC. (2013). MSDS Search & Product Safety. Retrieved 9 1, 2013, from Sigma-Aldrich: http://www.sigmaaldrich.com/safety-center.html?cm_mmc=Google_eBusiness-_-search-_-SIAL+Branded_Sial+Branded+MSDS-_-Sigma-Aldrich+MSDS_Phrase&cm_guid=1-_-100000000000000038125-_-23525955399
2. Queen 's University Department of Chemistry. (2013). CHEM/ENCH 212 Laboratory Manual 2013. Queen 's University.
3.NCSU Dept. of Chemistry. (n.d.). Retrieved 10 5, 2013, from ncsu.edu: http://ncsu.edu/project/chemistrydemos/Organic/SN1tBuCl.pdf
4. Sibert, G. (n.d.). Reaction Order. Retrieved 10 6, 2013, from http://www.files.chem.vt.edu/RVGS/ACT/notes/rxn_order.html
5. Carey, F. A. (n.d.). Chapter 8: SN1 Mechanism. Retrieved 10 6, 2013, from On-Line Learning Center for Organic Chemistry: http://www.mhhe.com/physsci/chemistry/carey5e/Ch08/ch8-2.html
6. Oyvind Eraker, K. S. (2011). CSTR Study: The Reaction of t-butyl chloride and Water.
7. D. Oancea, A. R. Conductometric Investigation of Enzymatic Urea Hydrolysis in a Self Buffering System.
8. Chohan, H. Q. (2010). Conductometric Titrations. Retrieved 10 7, 2013, from http://ceulk.weebly.com/uploads/3/1/3/8/3138840/conductometric_titration.pdf
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