Bridgehead solvolys

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University of Maryland, Baltimore County *

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306

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Chemistry

Date

Dec 6, 2023

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docx

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3

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Bridgehead solvolysis. Kinetics of S N 1 reaction. Post-lab questions. (1) Plot ln(1-V/V ) vs time (in seconds). Perform linear regression and determine slope. Paste the plots to your post-lab paper. A B Time (in seconds) ln(1-V/V ) 10 -0.058 74 -0.0811 287 -0.09056 526 -0.1145 801 -0.144 1293 -0.1694 A B T(in seconds) ln(1-V/V ) 20 -0.0339 22 -0.06899 25 -0.105 42 -0.143 50 -0.1823 50 -0.2231 70 -0.2657 90 -0.3102 112 -0.4055
(2) Using slopes determine rate constants k for both bromides (remember about using Winstein-Grunwald equation for t -butyl bromide). Compare k you determined for both 1-bromoadamantane and tert- butyl bromide. Which reaction is faster? Which carbocation is more stable? Explain briefly why. Solvolysis of 2-bromo-2methypropane in 80% ethanol was faster than the 40% ethanol. The slope of a graph represents the rate of reaction. The slope for 2-bromo-2methylpropane is higher than the slope for 1-bromoadamantane, which means the reaction of 2-bromo-2methylpropane is occurring at a faster rate compared to 1-bromoadamantane. The rate constant (k) for tert-butyl is higher than the rate constant for 1-bromoadamtane. This means that the reaction with tert- butyl happened faster compared to the reaction with 1- bromoadamantane. The reason is that the difference in reaction rate is that 1-bromoadamantane can’t adopt a planar geometry, which affects its ability to form a more stable carbocation. Also, 1-bromoadamatane is higher in energy and less stable because it formed slower during the experiment. (3) Look at correlation coefficients r (or R in some programs) for both regressions (or alternatively, visually assess how well your data points fit the straight line). How close is r to 1 (if r = 1, then it means that all points are on the straight line, if r = 0, it means that there is no linear correlation for your data). Good linear correlation means r > 0.9). Discuss what factors or experimental errors may diminish r (causes deviation of your data points from linearity). Graph B (R=0.9716) has a higher correlation coefficient (R=0.9569, which indicates a stronger linear correlation compared to graph B. Factors or experiment errors that may diminish the correlation coefficient include outliers,
measurement errors, or the presence of other variables that affect the relationship between the variables being studied. These factors can cause the data points to deviate from linearity and result in a lower correlation coefficient. (4) Below you see two bromides A and B. One of these bromides reacts thousands of times faster than other in solvolysis reaction (in EtOH/H 2 O). Predict which bromide reacts faster and explain your reasoning. Bromide B should be more reactive than A because it is more stable planer and more reactive.
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