from Microscale and Miniscale Organic Chemisty Lab Experiments,by Schoffstall, G
ID: 547012 • Letter: F
Question
from Microscale and Miniscale Organic Chemisty Lab Experiments,by Schoffstall, Gaddis & Druelinger, 2e. McGraw-Hill, Boston 2004) Part A. Effect of Structure of the Alkyl Halide in SN2 Reactions Measure 2 mL of 15% sodium iodide in acetone into each of three clean, dry 10-cm test tubes. *Close the cap on the container to avoid loss of volatile acetone** 1) Add 2 drops of 1-bromobutane to the first test tube; 2) Add 2 drops of 2-bromobutane to the second test tube; 3) Add 2 drops of 2-bromo-2-methylpropane to the third test tube. cap on the container to Stopper the three tubes with corks and shake to mix. Observe closely during the first 15-20 minutes, then at intervals throughout the lab period. Observe the test tubes for a sign of a reactior in the form of cloudiness or precipitation. Record your observations and the timing. Part B. Effect of the Leaving Group in SN2 Reactions Measure 1 mL of 15% sodium iodide in acetone into each of two clean, dry 10-cm test tubes. "Close the cap on the container to avoid loss of volatile acetone* 1) Add 2 drops of 1-bromobutane to the first test tube; 2) Add 2 drops of 1-chlorobutane to the second test tube; Stopper the tubes and shake to mix. Observe closely and record your observations. Part C. Effect of Structure of the Alkyl Halide in Svl Reactions Measure 2 ml. of 0.1 M silver nitrate in ethanol into each of three clean, dry 10-cm test tubes. 1) Add 1 drop of 1-bromobutane to the first test tube; 2) Add 1 drop of 2 bromobutane to the second test tube; 3) Add 1 drop of 2-bromo-2-methylpropane to the third test tube. Stopper the three tubes form of cloudiness or precipitation. Record your observations and the timing. and shake continually. Observe the test tubes for a sign of a reaction, in the Part D. Effect of the Leaving Group in S1 Reactions Measure 2 ml. of 0.1 M silver nitrate in ethanol into each of two clean, dry 10.em test tubes. 1) Add 1 drop of 2-bromo-2-methylpropane to the first test tube 2) Add 1 drop of 2-chloro-2-methylpropane to the second test tube Stopper the tubes and shake to mix. Observe closely and record your observations. Clean-up/Waste All SN2 reaction tubes can be emptied into the "halogenated waste" jug and rinsed · with acetone. All SN1 reaction tubes must be emptied into the "Ag waste" bin at the front of the room Wear gloves: Ag solutions will temporarily stain your skin.Explanation / Answer
Q: 1
ANS:
It is important to use a test tube that is dry because sodium iodide has ionic bonding. Water will break it apart, thereby influencing the results of the experiment. Also acetone is a polar aprotic solvent, whereas water is polar protic. This could affect the products, and also the speed of the reaction.
Q: 2
ANS:
(Fastest) 1-bromobutane > 2-bromobutane > 2 bromo-2- methylpropane (slowest)
For any SN2 reaction, primary alkyl halides reacts faster with NaI/ethanol as bromo is a better leaving group and it leaves easily in case of primary halide than secondary than tertiary. In the SN2 reaction, the big barrier is steric hindrance. Since the SN2 proceeds through a backside attack, the reaction will only proceed if the empty orbital is accessible. The more groups that are present around the vicinity of the leaving group, the slower the reaction will be. That’s why the rate of reaction proceeds from
primary (fastest) > secondary >> tertiary (slowest)
Q: 3
ANS:
Good leaving groups are weak bases. Some examples of weak bases: halide ions (I-, Br-, Cl-) and sulfonates such as p-toluenesulfonate (OTs) and methanesulfonate (OMs).
The weaker the base, the better the leaving group. On the other hand, strong bases are bad leaving groups.
Q: 4
ANS:
In SN1 reaction, the alkyl halide trend is
tertiary (fastest) > secondary >> primary (slowest)
The bulky groups pushes the leaving group to leave, thereby welcoming the nucleophile. Whereas primary alkyl halides has slowers reaction rate.
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