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I need help understanding the mechanism for thisproblem. I am thinking that the OH deprotonates thealpha carbon and then the electrophilic alpha carbon will attackthe carbon at the carbonyl at point "A." I am stuck atthis point, how do we get rid of the negative O? Can youplease draw out the mechanism for this problem?



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Patrina Schowalter
Patrina SchowalterLv2
13 Jun 2019

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Related questions

47

EXPERIMENT

9

Williamson Ether Synthesis

Reading and Preparation

TaskSource

S

-

115

Safety

Chemwatch

(website)

Background

In today’s laboratory class you will preparetert

-butyl methyl ether from potassiumtert

-

butoxide

and iodomethane using the Williamson ether synthesis according to Scheme 1. This is classified

as a substitution reaction of an alkyl halide, where iodine

in

iodomethane is replaced by a

tert

-

butoxide group.

Scheme 1

Substitution reactions of alkyl halides can occur by either an SN1 or S

N2 mechanism. In the SN1process, the rate-determining step in the reaction is breaking of the carbon-halogen bond and the

formation of a carbocation intermediate (Scheme 2).Scheme 2Such reactions follow first order kinetics because the rate of the reaction only depends on the

decomposition of one molecule and is therefore only affected by the concentration of the alkylhalide. In the SN2 mechanism,

the rate-determining step is the displacement of the halide by an attacking nucleophile (Scheme 3).

Scheme 3

This reaction follows second order kinetics because the rate depends on the interaction between

two molecules and thus the concentration of both the alkyl halide and thetert

-

butoxide

nucleophile. Nucleophilic substitution reactions are discussed in McMurry,

Chapter 11, pages

C

H

I

H

H

+

C

H

3

C

O

H

3

C

H

3

C

C

H

H

H

C

H

3

C

O

H

3

C

H

3

C

K

+

KI

HOC(CH

3

)

3

C

H

H

H

+

I

C

H

I

H

H

C

H

I

H

H

C

H

3

C

O

H

3

C

H

3

C

C

H

3

C

O

H

3

C

H

3

C

C

H

H

H

+

I

48

372

–

395. You will follow the progress of the reaction between potassium

tert

-

butoxide and

iodomethane in order to determine the mechanism of this reaction. If the reaction follows first

order kinetics, then the reaction occurs by the

S

N

1 mechanism. If the reaction follows second

order kinetics, then the reaction occurs by the S

N

2 mechanism.

The progress of the reaction is monitored by following the change in concentration of the

reactants over time. For this experiment, aliquots of the reaction mixture are withdrawn every

10 minutes for the first hour and every 20 minutes for the second hour

. The aliquots of reaction

mixture are placed in cold water to stop the reaction. The unreacted

tert

-

butoxide ions present

reacts with water to liberate hydroxide ions (Scheme 4).

Scheme 4

(H

3

C)

3

CO

̄

+ H

2

O

→

(H

3

C)

3

COH + HO

̄

Hydroxide ion is then t

itrated using standardised sulfuric acid and the concentration of the

tert

-

butoxide ion and iodomethane for each time can be calculated.

Notes

:

1.

The concentration of the

potassium

tert

-

butoxide

stated on the stock bottle

cannot be relied

upon as the

solution begins decomposing once prepared. For this reason you will need to

take a 1.00 mL aliquot of the stock solution and quench this in cold water. This solution

will then need to be titrated against the standard H

2

SO

4

solution to get the correct sto

ck

concentration of

tert

-

butoxide

. Note also this is

not

the concentration of the (H

3

C)

3

COK at

time zero in the reaction mixture

–

the (H

3

C)

3

COK solution has been mixed with the CH

3

I

solution in the reaction flask. Thus an appropriate calculation needs t

o be done to get the

(H

3

C)

3

COK concentration in the reaction mixture at time zero.

2.

The concentration stated on the bottle for the stock CH

3

I solution can be used but again note

that the time zero concentration of the CH

3

I in the reaction mixture is not th

is value.

Remember the CH

3

I solution is mixed with (H

3

C)

3

COK solution in the reaction flask so an

appropriate calculation needs to be carried out to get the time zero concentration for the

CH

3

I.

Record the initial concentrations of your two solutions and

the standard sulfuric acid as

shown below and d

raw

a

table in your laboratory notebook

or prepare an excel

spreadsheet

.

Initial Concentration of (H

3

C)

3

COK in (H

3

C)

3

COH

Initial Concentration of CH

3

I in (H

3

C)

3

COH

Concentration of standardised H

2

SO

4

You will use the data calculated in the table to draw 2 graphs. A plot or time versus log [CH

3

I]

will give a straight line if the reaction is first order.

A plot of time versus log ([(H

3

C)

3

CO

̄

] / [CH

3

I]) will give a straight line if the reaction is second

order.

49

Experimental

*

Note that the melting point of (H

3

C)

3

COH is 23

o

C

–

26

o

C. It may solidify if the room

temperature is cool, so keep all solutions warm.

*

Work in pairs for this experiment.

In separate conical flasks, place iodomethane in

tert

-

butanol (200.0 mL) and potassiumtert

-

butoxide intert

-

butanol (20.0 mL). If not already warmed, place the separate solutions in a water

bath (~40

o

C) for a few minutes. Start

timing on

the stop

-

watch as you quickly combine the

solutions, swirling to mix them thoroughly. Place the reaction vessel in the water bath to

maintain constant temperature. Prepare a conical flask containing cold water (20.0 mL). After

10 minutes pipette an aliquot of th

e reaction mixture (10.0 mL) and run it into the cold water to

quench the reaction. Later you can add phenolphthalein indicator and titrate the liberated

hydroxide ion using the standardised sulfuric acid. After removal of each aliquot the pipette

should

be thoroughly rinsed with water and acetone. The pipette can be dried if necessary by

blowing air through it using the house compressed air and appropriate tubing. Remove aliquots

every 10 minutes for the first hour and every 20 minutes for the second h

our. Write the sulfuric

acid titres in your table, carry out all necessary calculations and plot the graphs.

Questions

1.

By what mechanism would you expect the reaction between potassium

tert

-

butoxide

and iodomethane to proceed? Explain your answer and

write the curved arrow

mechanism.

2.

Do your results support your prediction? If not, offer some possible explanations.

3.

Provide a sample calculation of each of the cells in the spreadsheet for one time

interval. Show the formulae used for each calculation

Please help me finish lab...my lab stopped working and I can'tget the labs to finish. I highlighted and underlined my answers. Ibolded the questions that I could not finish.

1-4: Investigating the Properties of Alpha and BetaParticles

As scientists began investigating the properties of atoms, theirfirst discovery was that they could extract

negatively charged particles. They called these particleselectrons, but they are also known as beta

particles in the context of nuclear decay. Robert Millikan usedbeta particles in his famous Oil Drop

Experiment. Another particle ejected during nuclear decay is thealpha particle. An alpha particle is a

helium nucleus, or a helium atom without its two electrons.Consequently, an alpha particle is positively

charged. Ernest Rutherford used alpha particles in his Gold FoilExperiment.

1. Start Virtual ChemLab and select Alpha and BetaParticles from the list of assignments. The lab will open inthe Quantum laboratory.

2. What source is used in this experiment? Drag yourcursor over the source to identify it.

ElectronGun

What type of charge do electrons have? Negative

What detector is used in this experiment? A phosporScreen

3. Turn on the Phosphor Screen. (Click on the green/redbutton.)

What do you observe? A dot in the center of thescreen

The phosphor screen detects charged particles (such aselectrons) and it glows momentarily at the positions where theparticles impact the screen.

4. Drag the lab window down and left and the phosphor screenwindow up and right in order to

minimize the overlap. Push the Gridbutton on the phosphor screen, and set the Magnetic Fieldto 30

?T. (Click the button above the tens place three times. If youmistakenly click between digits, it will

move the decimal point. Click it to place it where it wasoriginally and then click above the tens

place.)

What happens to the spot from the electron gun on thephosphor screen? the dot moves to theright

5. Click once above the tens place on the ElectricField meter. Observe the spot. Click a second time

above the tens place on the Electric Field.

What happens to the spot from the electron gun on thephosphor screen? The dot moves to theleft

6. Zero out the Magnetic Field and ElectricField meters by clicking on the appropriate digit buttonsuntil the spot on the phosphor screen is centered again.

7. Double-click or click and drag the electron gun to move it tothe Stockroom counter. Enter the Stockroom byclicking inside the Stockroom. Double-click the electrongun to move it back to the shelf. Double-click on the alpha sourceto select it and move it to the Stockroom counter. Clickon the green Return to Lab arrow to return to the lab.Drag the alpha source from the Stockroom counter and placeit on the table where the electron gun was originally placed (themiddle spot light). Click on the front of the alpha source to openthe shutter.

What appears on thephosphor screen?

Atomic Theory

8. Change the unit for the Magnetic Field from ?T to mTby clicking once above the unit. Click above the hundreds placethree times to set the Magnetic Field to 300 mT(millitesla). This magnetic field is one million times strongerthan what we used for the electron gun.

Whichdirection is the spot deflected when the magnetic field isincreased this time?

How doesthis compare with the direction of movement when the magnetic fieldwas turned on for the electrons?

9. Change the unit for the Electric Field from V to kVby clicking once above the unit. Observe the spot as you increasethe Electric Field strength from 0 kV to 5 kV. Themovement is slight so pay careful attention.

Whichdirection is the spot moved when you increase the ElectricField?

How doesthis compare with the direction of movement for the electron beamin the Electric Field?

Why does ittake significantly stronger magnetic and electric field strengthsto move the beam of alpha particles compared with the beam ofelectrons (beta particles)?

10. Return the values on the two meters to zero. Double-click(or click and drag) the alpha source and the phosphor screen toreturn them to the Stockroom counter. Enter theStockroom. Double-click on the alpha source and thephosphor screen to place them on the shelf. Select the laser andthe video camera by double-clicking on them, and then click on thegreen Return to Lab arrow to return to the lab. Place thelaser in the center spotlight on the left and turn the laser on(click on the red/green light). Place the video camera on thecenter spotlight on the right and click the video camera to turn iton. Set the laser intensity to 1 nW and the wavelength to 20 nm.This wavelength is in the x-ray region of the electromagneticspectrum. The purple dot is a representation of the x-rays hittingthe video camera. Change the Electric Field andMagnetic Field to determine the effect on the x-rays.

Did theelectric or magnetic fields affect the x-rays? Why or whynot?

Summarizewhat you have learned about electrons (beta particles), alphaparticles, and x-rays.


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