SN2 post lab
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Jan 9, 2024
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SN2 Post Lab
Suzanne Varughese
CHEM 301, L16
1.
This synthesis is an example of an Sn2 mechanism. What are the hallmarks of Sn2 compared to Sn1? First the procedure of Sn2 compared to Sn1 is completely different. For Sn2 we had to perform reflux and distillation for the solution, unlike Sn1 in which we performed
different small reactions. Another hallmark is that Sn2 reactions are favored with primary carbon substrates. 1-butanol is a primary alcohol in our experiment, unlike Sn1 mechanism that uses a tertiary carbon substrate.
2.
Write a formal procedure for this experiment. Use the modifications that were made in lab (ie base it on the procedure you actually did in lab).
6.2 mL of 1-butanol was placed into a 100 mL round bottom flask. Subsequently, 10 mL of 48% hydrobromic acid (HBr) was added to the flask while swirling. A cautious and slow addition of 4 mL of concentrated sulfuric acid (H2SO4)
to the flask was performed with swirling. In case the flask became excessively hot, it
was cooled in an ice bath. A stir bar was added to the flask, and a reflux condenser was connected to the top of the round bottom flask. The water hoses were connected to the condenser, with water entering through the bottom nozzle and exiting through the top nozzle. Once the apparatus was connected, the reaction mixture was heated at reflux for 30 minutes. Subsequently, the flask and its contents were allowed to cool to nearly room temperature using an ice bath. 10 mL of de-ionized water was slowly, carefully, and with swirling, added to the mixture through the condenser. The apparatus was converted to a simple distillation. The contents of the flask were distilled into a 25 mL round bottom flask immersed in an ice bath. Distillation was stopped when the temperature of the distillate reached 96C, due to it being distilled for 20+ min. The aqueous layer was removed from the distillate using a transfer pipet. Then, 5 mL of de-ionized water was added to the organic layer of the distillate, mixed well with the transfer pipet. The aqueous layer was separated from the organic layer. The aqueous layer was combined with the original aqueous layer. The organic layer was washed with 5 mL of 5% sodium bicarbonate solution, and the layers were separated, combining the aqueous layers in a "waste flask." The organic layer was washed once more with 5
mL of de-ionized water, separating the layers, and combining the aqueous layer with the other aqueous washes. The organic layer was dried over anhydrous sodium sulfate. The dry organic layer was decanted or pipetted into a clean, dry, 44.12 g round bottom flask. The product was weighed at 1.199 g, and an IR spectrum was run on the product. 3.
Calculate theoretical yield of 1-bromobutane using 1-butanol as the limiting reagent.
4.
Calculate the percent yield of 1-bromobutane.
5.
Attach your IR and identify the peaks that belong to 1-bromobutane and what bonds they correspond to.
A strong peak between 2850-3000 cm
-1
would be the peaks that belong to 1-
bromobutane, because that’s where an alkane (C-H stretch) strength is shown. 6.
Explain the difference in IR between 1-bromobutane and 1-butanol
Unlike 1-bromobutane, 1-butanol has an -OH group attached to the compound. The
IR spectrum in 1-butanol would show sharp/broad around 3200-3650 cm
-1
. Another difference would be 1-bromobutane would show strong, sharp peaks around the 300-500cm
-1
region because of the C-Br bond stretch. 7.
Based on your IR, do you think 100% of the water was removed from the organic layer? Why/why not? Based on the IR graph, I believe that around 100% of the water was removed from the organic layer. In an IR spectrum graph, O-H stretching in the range of 3200-3650
cm
-1
would indicate the presence of H
2
O. In this graph, I can see that there is no strong, sharp peak around this range. This indicates that there is lack of water present in the organic layer that ran through the IR spectrum.
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Which is the least reactive compound by the SN2 mechanism?
Br
I
CH3CH₂CHCH3
O b.CH3CH₂CH₂CH₂Br
a.
O c.
Br
CH3CH₂C(CH3)2
O d. (CH3)2CHCH₂Br
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know about substitution/elimination, what is the expected mechanism
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give the actual product of the reaction.
Br
ткон
s
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Br
tBuO
H3C
H3C
CH2
H2
Alkyl halides undergo nucleophilic substitution and elimination reactions. When the kinetics of the reaction are
measured, if the rate of the reaction is found
alkyl halide the reaction is second order. The substitution reaction is thus termed SN2, and the elimination reaction is
be dependent upon the concentration of the nucleophile as well as the
termed E2. These reactions are bimolecular and take place in a single step. In the SN2 reaction, the nucleophile attacks
the a-carbon from the backside and displaces the leaving group with an inversion of configuration occurring at the
carbon. In the E2 elimination reaction, strong base removes an acidic hydrogen from the B-carbon and an alkene is
formed as the leaving group is expelled from the a-carbon. This elimination follows Zaitsev's rule whereby the more
substituted alkene is generally formed. In E2 elimination, both the B-hydrogen and the leaving group must be oriented
anti to each other.
The same reaction…
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Br
reagent: Nal
solvent: acetone
d.
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Provide the full mechanism of this SN2 reaction.
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1. Reaction mechanism
2. Show sterochemistry
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In an E2 mediated elimination reaction of an alkyl halide (H-X) using NaOCH3 as
base, which of the following statement is not true?
O The reactivity order for alkyl halides (RX) is tertiary secondary> primary.
O The rate of reaction = k2 (alkyl halide] [NaOCH₂]
O The reaction occurs in a single step.
O The rate is independent of the leaving group.
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For each of the following reactions give the Major product(s) of the reaction only and statethe mechanism the reaction follows (SN1, SN2, E1, E2).
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was reading the organic chemical literature and was surprised to read that this structure reacts with good Lewis/attacker
nucleophiles rapidly by the SN1 pathway. Why was Prof. surprised by these data? Explain these data using your knowledge of SN1
pathways.
Prof.
Me
xo
Me
Me
OTS
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The following reaction occurs at room temperature in acidic solution, first forming
intermediate A, which then rearranges into final product B.
i. Show the mechanism for the formation of Intermediate A.
ii. Show the mechanism for the rearrangement of A to B (you have seen this
before!).
iii. Explain why the reaction does NOT occur readily in basic solution using your
mechanism from 2.a.1
1.
2.
A →
-OH
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нзод
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Below is the equation for a nucleophilic substitution reaction and some experimental data.
CH3CH2Br + CH3COO- ⇌ CH3CH2CO2CH3 + Br- ΔH=-75 kJ/mol
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Which reaction energy profile would be the best representative of the data provided?
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pls answer both questions
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3. Two reactions are given below. One reaction leads to product and the other does not and the starting material remains
unreacted.
i)
CI
NaOCH3
HOCH 3
ii)
NaCl
OCH 3 HOCH3
a. Draw a complete reaction scheme clearly showing all intermediate products in the space below for the reaction that
proceeds to product.
b. Draw a reaction coordinate diagram for the forward reaction above from the starting material given to your product
showing all intermediates produced along the reaction coordinate. Be sure to label your axes and to think about how the
potential energy changes along the reaction coordinate.
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Which is the most reactive compound by the SN1 mechanism?
O a.
Br
I
CH3CH₂CHCH3
O b. CH3CH₂CH₂CH₂Br
O C. (CH3)2CHCH₂Br
O d.
Br
CH3CH₂C(CH3)2
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9.
The initial rates for the following two elimination reactions were measured under different
concentrations of the electrophiles and bases (H2O in the top reaction, KOCH2CH3 in the bottom
reaction; all data is presented in the two tables. For each reaction, top and bottom, does the data suggest
an El or E2 reaction pathway (rates are all 10* units)? Explain. Write the rate equations for each
reaction.
Trial Number [R-OCH.]
[H,0]
Rate (M/s)
0.010 M
0.45 M
9.50 X 10-4
HO
2
0.020 M
0.45 M
1.85 x 10 3
CH,CN, H
OCH,
0.22 M
1.85 x 10-
3
0.020 M
Trial Number R-Br]
[KOCH,CHal
Rate (M/s)
6
1.0 M
1.0 M
2.35 X 10
Br
0.50 M
0.50 M
5.9 x 10*
+ KOCH,CH,
CH,CH,OH
3
0.50 M
1.0 M
1.20 x 10
Top Reaction:
Bottom Reaction:
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1. NO+H2→N+H2O2. NO+H2→N+H2O
1. NO+H2O→NO2+H22. NO2+H2→N2+H2O
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