Kinetics Of Nucleophilic Substitutions

Kinetics Of Nucleophilic SubstitutionsThe study of dynamics involves the observation of the chemical response range and the factors that promote or diminish down those treasures. In addition to providing companionship about the process replys reactant to product translation, but it is alike sustainful in increasing efficiency in the manufacturing world as kinetics provides breeding about how long a response will take and if it take places at all. Hence, it is crucial steady from a financial aspect that kinetics is studied.1This examine exhibits the kinetics of a nucleophilic substitution reception. The purpose of this experiment is to investigate the kinetics of the hydrolysis of t-butyl chloride which solvolyzes by an SN1 mechanism beca hold t-butyl chloride is a tertiary halide ( alkyl radical halide). SN1 mechanism means a first drift chemical reaction with substitution by a nucleophilic result. The boilersuit reaction is as follows t-butyl chloride + H2O - (CH3)3C OH + HCl. The mechanism involves a first ordinate-determine slow step which ionizes t-butyl chloride and produces a chloride anion and carbocation. This is stray determining step because the rate of reaction depends on the alkyl halide and non on the nucleophilic solvent. The ionisation is as follows t-butyl chloride - (CH3)3C+ + Cl-. Thus, the rate of reaction (rate of disappearance of preoccupancy of t-butyl chloride) corresponds to the concentration of t-butyl chloride. The back up step involves the nucleophile and is luxuriant and as follows (CH3)3C+ + Cl- + H2O - (CH3)3COH + HCl. These reactions, at specific known temperature, will help the experimenter obtain the consume beat it takes for the reaction to occur which in change form will help calculate the rate continuous, k. Using the Arrhenius equation, the rate incessant k will help calculate the activation susceptibility.2This experiment demonstrates the correlational statistics between var. in concentration (b oth t-butyl and hydroxide), temperature, solvent preindication, and substrate complex body part with the rate of reaction of the hydrolysis of t-butyl chloride as well as exhibits the kinetic order of the reaction. The reactions are taken to increasing levels of completion (10%, 20%, and 30% completion) to concur sure that the rate constant K is steady at the same(p) temperature and reactant concentration. The activation energy the reaction requires in order to proceed is alike examined in this experiment.ExperimentalFor experiment run 2 of III. adopt of resultant Polarity, in order to make a 6040 (WaterAcetone) sample, 4mL of t-butyl chloride was interracial with 0.4 mL of 0.1 M NaOH and 5.6mL H2O. The reason was because 5.6 mL of irrigate + 0.4 mL of NaOH= 6 mL and 6 mL/ 10mL total volume of declaration = 60% water 4 mL of t-Butyl chloride = 4 mL and 4 mL/ 10 mL total volume of tooth root= 40% dimethyl ketone.The experimental procedure carried out for this science lab followed the steps listed in the lab manual. attend to Organic Chemistry Lab Manual Fall 2010 Winter 2011 pages 21-22.Results abide by All the declarations turned a bit lime-green before turning sensationalistic. The measure measured for reaction to occur corresponds to the m it took the solution to turn yellow in colour. analyse of answer OrderVariation of Hydroxide duckingRUN% CompletionTime (seconds)k (s-1)110492.15 x 10-3220942.37 x 10-33301512.36 x 10-3Note Refer to Appendix for calculation of rate constant kVariation of t-Butyl Chloride ConcentrationRUNt-Butyl Chloride in stock solutiont-Butyl Chloride in reaction solutionTime (s)K (s-1)Rate of Reaction(M/s)Reaction order of t-butyl chloride10.2 M0.06 M271.90x 10-31.11 x 10-41storderPART A, RUN 10.1 M0.03 M492.15x 10 -36.12 x 10-51storder20.1 M0.015 M641.65x 10-32.34 x 10-51storderNote Refer to appendix for calculation of t-butyl chloride in reaction solution, rate constant k, rate of reaction, and reaction order of t -butyl chloride.Study of Temperature Variation (Room Temperature 19.5C)RUNTemperatureTime (seconds)1aRoom temp. 10o =(9.5oC)1211bRoom temp. 10o =(9.5oC)123Part A, enumeration 1Room temp. = (19.5oC)492aRoom temp. + 10o= (29.5oC)202bRoom temp. + 10o=(29.5oC)20Study of Solvent PolarityRUNWater Acetone epoch (seconds)180 2022Part A, Run 170 3049260 40134Study of Structural Variations in the SubstrateRUNSubstrateTime (seconds)1Isopropyl ChlorideNo reaction (Waited for 7 minutes and nothing happened. The reaction categorization was even heated on a steam bath)Calculating activating Energy (Ea)Note The data of the Runs are from the Study of Temperature Variations.Runk (s-1)Average k (s-1)- lumber kT (C)1/T (C-1)1a8.71 x 10-48.64 x 10-43.069.50.10531b8.57 x 10-4Part A, Run 12.15 x 10-32.15 x 10-32.6719.50.05132a5.27 x 10-35.27 x 10-32.2829.50.03392b5.27 x 10-3Note - put down k column was plan on the y-axis and 1/T was plotted on the x-axis of Figure 1Figure 1 This figure represents th e graph of 1/Temperature against - log K, which is used to match the activation energy of the reaction. A line of best fit is lay downn to show the equation of the line, which is y=10.049x + 2.0321. The fallacy of the graph is represented by R2. The peddle of 10.049 is equal to Ea/2.3R. Hence, the activation energy (Ea) of the reaction is equal to 45.76cal/mole with an error of 4.19cal/mole.Reaction MechanismDiscussionThe first part of the experiment placid of study of reaction order. During part A of this experiment, when the hydroxide concentration was wide-ranging (which corresponded to a different tally of completion of reaction), it was observed that the k set were all very close (around 2.3610-3 s-1). Since the rate constant, k, is an integral part of the rate of reaction, the similar k values indicate that the NaOH concentration in the solution has no effect on the rate of reaction. This is because the nucelophile is not involved in the first step (rate determining) a nd tho reacts to the substrate which occurs during the second (fast) step.3 This shows that the reaction is naught order when looking at the concentration of the nucleophile. It makes sense since the rate determining steps are the slow steps and in this reaction, the first ionization step is the slow step, thus making it the rate determining one. Meanwhile, the second step is fast and so it is not the rate determining one. Hence, since the nucleophile is only when present in the second step (NaOH is neutraulized by the HCl formed in the fast second step)2, it is not linked to the rate of the reaction (NaOH concentration does not relate to the rate of reaction).During part B of this experiment, t-butyl chloride concentration was varied. It was seen that the reaction time kept drastically morose when as the concentration of the t-butyl chloride in the reaction solution change magnitude. Refering to T adapted-bodied 1, the fastest reaction (in lowest quantity of time of 27 secon ds) occurred when the concentration of t-butyl chloride was relatively highest (0.06 M), followed by a laggard reaction (49 seconds) when concentration of butyl in reaction solution was lower (0.03 M), and ultimately followed by the slowest reaction (64 seconds) when the concentration was the lowest (0.015 M). Hence, this clearly proves that the substrate had a major effect on the rate of the SN1 reaction. Referring to Table I (b), it was calculated that the rate order of t-butyl chloride was the one. This in turn also proves that the general reaction is first order as the rate of the reaction is only affected by concentration of one molecule, that being the substrate, which in this gaucherie was t-butyl chloride.Experiment two showed the effect of temperature variation on the reaction. The room temperature of the lab was at 19.5C. At the lowest experimented temperature, 9.5C, the k value of the reaction was 8.64 x 10-4 s-1 (referring to Table V). When the experiment was perform ed at the room temperature of 19.5C, the k value augment to 2.15 x 10-3 s-1. While at the highest experimenting temperature, 29.5C, the k value of the reaction was seen to be the highest at 5.27 x 10-3 s-1. From this it sens be concluded that as the temperature increased, the k value of the reaction increased as well. Referring to Table 2, it can also be noted that, as the temperature increased, the time of reaction decreased significantly. These do are due to the fact that increase in temperature causes greater amount of reactant molecules to gain enough kinetic energy to overcome the activation energy required of the reaction (enough energy to go through the first rate-determining step).4 As a result, an increase in temperature corresponds to an increase in the number of roaring collisions among the reactant molecules. Thus, the reaction would occur faster and so the time for the reaction to occur would decrease. Referring to Figure 1 (Arrhenius plot), the activation energy of the reaction was calculated to be 45.76cal/mole with an error of 4.19cal/mole.The third experiment showed the effect of solvent frigidity on the reaction. It was observed that, as the ratio of water to acetone decreased, the time of the reaction increased, and so, the rate of the reaction decreased. This is probably due to the fact that water have high polarity than acetone as water acetone has a longer hydrocarbon chain than water. Since the reactant in this experiment, t-butyl chloride, is a slightly polar molecule, its polar nature during the transition state of the reaction increases tremendously. As a result, water (with comparatively much higher polarity), will allow increased salvation of the carbocation and centiliter anion that formed during the first rate-determining ionization step, by lowering the energy of the transition state. This is because water, a protic solvent, forms hydrogen bonds with both of the aforementioned ions in order to increase the solvolysis. Whi le acetone is an aprotic solvent and not able to form the hydrogen bonds. Hence, higher ratio of water to acetone of a solvent is expected to result to a higher rate of hydrolysis reaction due to a better ability to solvate charged intermediate, which is just what was observed in experiment.5The last experiment showed the effects of structural variation in the substrate on the reaction. In this experiment, t-butyl chloride was replaced with isopropyl chloride. As a result, no reaction took place after 5 minutes of waiting and even after heating it for 7 minutes. This is due to the fact that isopropyl chloride is a utility(prenominal) halide while t-butyl is a tertiary halide. The t-butyl chloride was able to react because it was able to build a stable carbocation as it had a tertiary carbon which allows hyper wedlock and generalisation to occur. While on the other hand, isopropyl results into a far slight stable carbocation as it does not allow for enough hyper conjugation and induction as it does not have any C-C sigma bonds that t-butyl chloride has. The t-butyl chloride would form more substituted carbocations than isopropyl. As a result, it is favourable to form a carbocation with t-butyl chloride than with isopropyl chloride as tertiary halides undergo SN1 reactions more efficiently.The results of the experiment seem to agree with the expected results. Though, thither can always be sources for errors while performing all of the experiments. First of all, to cause the different type of mixtures, amounts of contents had to be made through the use of instruments such pipette and graduated cylinder. Since these instruments required the experimenter to estimate each measurement with the naked eye and so this could have lead to improper solution mixtures. Another error that possibly occurred could have been with the use of a snatch watch. It was not possible to start the stop watch at the exact heartbeat that the two solutions were mixed and stop at t he exact instant the solution reached equilibrium. That could have lead to error in measuring time of reaction. Furthermore, the neutralization of NaOH was measured by timing the reaction until it turned into a yellow colour. Though, since the reaction solution progressively turned from a gloomful colour to a yellow colour, it was not possible to exactly estimate the end of neutralization. to a fault, during the study of temperature variation, it was not possible to keep the temperature to be incisively at the same temperature for the entirety of one run of experiment as the temperature showed slight variations every minute. Lastly, due to limited amount of Erlenmeyer flasks available for the experiment, flasks had to be reused. Even though all the flasks were thoroughly washed with wash solvent and rinsed. Hence, this could have possibly caused contaminations which lead to errors in results. Overall, due to various reasons, there could have been errors in timing which would lead to improper calculation of rate constants and activation energy of the reaction.QuestionsI)Let ln (x) = yx = eylog (x) = y*log(e)log (x) = ln(x)*log(e)ln (x) = log(x)/log(e)ln (x) = 2.303 log (x) since log(e) = 0.4343II) ln RCl0/RCl = ktLet x = RCl0/RClln (x) = ktln (x) = 2.303 log (x)kt = 2.303 log (x)kt = 2.303 log ( RCl0/RCl )kt = 2.303 log ( 1/ RCl ) let RCl0 = 1 (because initial concentration is 100%)kt = 2.303 log ( 1/ 1 difference in RCl )because RCl0 RCl = difference in RCl1 RCl = difference in RCl1 difference in RCl = RClkt = 2.303 log ( 1/ 1 %reaction/100 )because %reaction/100 equals the difference in RClAn apolar solvent would hinder SN2 reaction as it would not be able to solvate the reactant due to the fact that it would repel the anionic nucleophile. And since nucleophilic reactions require the solvation of reactants, SN2 reaction would not take place.Polar protic solvents are usually acceptable for SN2 reaction as they are convenient solvents for nucleophilic s ubstitutions because the reagents are soluble. The high polarity would turn the solute. Small anions are solvated more than large anions. Though, these solvents would result into slower reaction due to hydrogen bonding which causes loss of nucleophilicity.Polar aprotic solvents prefer SN2 reactions as SN2 reactions prefer the basic nucleophilic. The aprotic solvents enhance the nucleophilicity of anions and have strong dipole moments. Also since these solvents do not have OH or NH groups, no hydrogen bonds mustiness be broken to make room for nucleophile to attract to electrophilic carbon atom. This is the nearly preferred solvent for SN2 reactions.6Alkyl iodide contains iodine atom, while alkyl chloride contains centilitre atom. Iodine has lower electro-negativity (2.5) than that of chlorine (3.0). Hence, alkyl iodide would be a less(prenominal) polar compound. Since water is a highly polar solvent, it will not be able to solvate alkyl iodide as much as alkyl chloride due to hi gher attraction to the more electro-negative atom of chlorine than that of iodine. As a result, it will not be able to increase the salvation of the transition state as much as that of alkyl chloride which has higher polarity.2 Hence, the activation energy of the alkyl iodide would not be lower as much as that of alkyl chloride and so its Ea would be higher than 31 kJ/mol.Structure of bromophenol blue indicator at alkaline pH.7