CHE-313TENTATIVE SCHEDULESpring '13
sectiontopicreference
313-01313-02
0.1/211/22No Lab HOLIDAY
1. 1/23 1/24check-in, orientation
2.1/281/29Nitration Exp’t., arene prep. supplement
3.1/301/31Arene Oxidation/IR & nmrsupplement
4.2/042/05cont.IR/NMR SUP.
5.2/062/07cont.
6.2/112/12ID of unknown ketoneC=OList
7.2/132/14cont.supplement
8.2/182/19 No Lab HOLIDAY
9.2/202/21Reduct. of acetophenonesupplement
10.2/252/26cont.
11.2/272/28Esterificationsupplement
12.3/043/05cont
13.3/063/07Grignard synthesissupplement
14.3/113/12cont.
15.3/133/14Aldol condensationSUP.
16.3/183/19cont.
17.3/203/21Diels Aldersupplement
18.3/253/26Diels Alder cont.
19.3/273/28α,β-unsaturated ketoneSUP.
20.4/01, 4/034/02, 4/04No Lab SPRING BREAK.
21.4/084/09α,β-unsaturated ketone cont
22.4/10 4/11Lidocainesupplement
23.4/154/16cont.
24.4/174/18cont.
25.4/224/23Qualitative analysisSUP.
26.4/244/25
27.4/294/30
28.5/015/02
29.5/065/07
30.5/085/09Written Quiz, Check-Out
Pre-labs:
For each preparative lab you are required to submit at least 24 hours before the lab a pre-lab write-up. The pre-lab is to be written in your lab notebook and the carbon copies submitted for review. These carbon copies will later be attached to your lab report.
1. Title (be specific, eg. "Reduction of Acetophenone with Sodium Borohydride"), name & date.
2. Balanced chemical equation(s) for the reaction(s) that you are going to carry out.
3. Table of Physical Properties summarizing the physical properties of the reactants, solvents, and products. Make photocopies of the sample provided, or make up your own.
4. A step-by-step procedure for the reaction, separation, and purification. Be specific as to amounts (moles & weight or volume).
5. For multi-step syntheses prepare a separate Table of Physical Properties for each reaction in the sequence.
You may turn in pre-labs directly to the instructor or they may be placed in his mailbox in the Chemistry Office (NSM B-202). If you have not submitted a pre-lab before the lab you will not be allowed to begin the experiment until the pre-lab has been completed and okayed. Failure to submit pre-labs on time can severely affect your grade.
Lab Reports
A typed lab report is required for each experiment and is worth 20 pts (180 pts total) or approximately 45% of your total course grade. Reports are due one week after the scheduled completion of the experiment at 1:00 pm for section 01 and 9:00 am for section 02. Labs turned in after these times will be penalized 10% per day late.
Follow the following format for preparative reports:
1. Title, name & date (unknown #)
2. Balanced equation(s) for the reaction(s) you carried out.
3. Step-wise mechanism(s) for the reaction(s).
4. Physical data for your product(s) (weight, mp or bp, %yield, & literature mp or bp for comparison).
5. Tabulation of spectral data. (Tables summarizing the IR and nmr spectra and your interpretation). see attached.
6. Conclusions, comments, deviations, etc. Discuss your results.
7. Answers to the questions at the end of each preparation.
8. Attach to the end of the report:
a) the pre-lab including table of physical properties
b) any additional carbon copies from your lab notebook
c) IR & nmr spectra, glc's, etc.
Products
With your lab reports you are to turn in the products that you have synthesized in the laboratory. Note, the labels must contain your name, the date, the identity of the contents, the net weight, and the mp or bp. Solid products should be in wide-mouth bottles and liquids in narrow-mouth containers.
1
TABLE OF PHYSICAL PROPERTIES (This table must be completed before coming to lab!)
Reactants and MW Moles weight volume density bp mp solubility
solvents (g/mol) (g) (mL) (g/mL)(0C) (0C)
Product(s)
TABLE OF PHYSICAL PROPERTIES (This table must be completed before coming to lab!)
Reactants and MW Moles weight volume density bp mp solubility
solvents (g/mol)(g) (mL) (g/mL)(0C) (0C)
Product(s)
NITRATION OF A HALOARENE
NOTE
WEAR GLOVES AND LAB COAT DURING THE ENTIRE PROCEDURE
Haloarenes and their nitration products are irritating to sensitive skin areas. If you should have these materials on your hands and then accidentally touch your face, this can cause a severe burning sensation in the affected area. If this should happen,
IMMEDIATELY:
1. Go to the restroom and wash the affected area with lots of soap and water.
THE SOAP IN THE LAB IS NOT SUITABLE FOR THIS PURPOSE.
2. Return to the lab and apply mineral oil to the affected area.
3. The summary to this warning is NOTTO TOUCH ANY PART OF YOUR BODY
WHILE PERFORMING THIS EXPERIMENT.
If you must leave the lab for any reason:
1. First dispose of your gloves in the waste container
2. Immediately go to the restroom and wash your hands
thoroughly with soap and water.
AGAIN, LAB SOAP WILL NOT DO A SUFFICIENT CLEANING
JOB
3. Upon returning to the lab, obtain another pair of
gloves from the front of the room, and proceed with
the experiment.
NITRATION OF A HALOARENE
Equation:
H2SO4
RBr + HNO3 ------> RBrNO2 + H2O
Locker # / Compound1, 10, 20, 4 / 4 Bromobenzene
2, 12, 22, 9 / 1,4-Dichlorobenzene
3, 13, 19 / 1,3-Dichlorobenzene
5, 15 / 1-Bromo-4-chlorobenzene
6, 16, 11 / Chlorobenzene
7, 17, 21 / 1,4-Dibromobenzene
8, 18, 14 / 1,2 Dichlorobenzene
------FOR SAFETY REASONS ------
1. Add 700mL of tap water to your 1 L Beaker.
2. Discard any acid washings, plus the contents of the filter flask (from step 9 below) into your 1 L Beaker, WITH STIRRING.
3. Wash the contents of your 1 L Beaker down the sink.
PROCEDURE
1.Obtain 0.025 mole of your haloarene ( See table above ) to a small beaker/graduated cylinder, and place it in your
hood area.
2. Prepare a mixture of 5 mL conc HNO3 and 5 mL conc H2SO4 in a 25x150 mm test tube, take it back to your hood workstation and clamp it to your hotplate/stirrer, immersing the tube in a 150 mL beaker containing 100 mL tap water. Allow the tube to cool to 30 deg. C, measured using your glass thermomtter.
3. To the test tube, add your haloarene, gently stirring to mix the contents. Continue to stir/agitate the test tube contents until the haloarene begins to transform into solid nitrohaloarene immersed in the acid mixture. Keep the reaction mixture between 50 - 55 oC. DO NOT ALLOW THE REACTION MIXTURE TO EXCEED 60 oC.
4. After the exothermic reaction has subsided, heat the test tube for 10 min. on your hot plate set at ~ 2.5 to maintain the temperature below 60oC during this period.
5. Cool the test tube in an ice bath to room temperature
6. Pour the reaction mixture into 50 mL of distilled water which is in a 150 mL beaker.
7. Isolate the crude product by vacuum filtration.
8.Wash the filter cake thoroughly with cold (0-10oC) distilled water and dry the filter cake by allowing the vacuum apparatus to draw air through it after you have finished washing.
9. Place the washings into the 1L beaker. Transfer the crystals to a TARED 50 mL beaker and obtain the weight of your wet product
10. Calculate the volume of 95%(v/v) ethanol needed to just dissolve the halobromobenzenes. You will need approx. 5 mL 95% ethanol per gram of crude product. Round the amount of ethanol needed to the next 5 mL increment. (e.g.: 5.6 g. x 5 mL/g = 28 mL => use 30 mL). SHOW THIS CALCULATION IN THE PROCEDURE PORTION OF YOUR REPORT.
11.Bring this mixture to boiling to dissolve the crude product. If the product does not completely dissolve boiling, add 5 mL of 95%(v/v) ethanol. If solid still remains you will have to do a hot filtration. Once your crude product has dissolved, set the flask onto your lab bench and allow the contents to cool slowly to room temperature.
- Isolate the nearly pure crystals of your product by vacuum filtration. If there is solid material in the filter flask at this point, pour it into a beaker and vacuum filter this solution again through the funnel containing the first crop of nitrobromobenzene. Save the filtrate.
- Wash the crystals with a little ICE COLD ethanol, allowing the washes to drain into the filter flask containing the filtrate. The filtrate may now be poured into the recovered organic solvents container at the east end of the lab.
- Allow air to be drawn through the Buchner funnel for 5 min. then detach the vacuum hose from the filter flask, turn off the water and transfer the solid from the Buchner funnel onto 11cm filter paper which is on a watch glass. Spread the solid over most of the filter paper, breaking large clumps into small particles and put it in your drawer to dry overnight. Place another piece of filter paper lightly over the crystals to keep the dust out.
ThinLayer Chromatography
1.Take a few crystals of haloarene isomer, place in a 5 ml beaker, and add 5 drops of acetone to the beaker to dissolve the crystals. Do the same with your known haloarene standards
2.Take a 2.5 x 7.5 cm strip of silica gel, mark the origin 1 cm from bottom and make 2 pencil marks lightly on the origin.
3.Apply one drop of the solution containing the 4-nitro isomer on one spot & one drop of oil containing the 2-nitro isomer on the other spot. Be sure that neither application results in a spot more than 2 mm in diameter. Allow the strip to dry at your hood workstation .
4.Place dried strip in jar containing the solvent solution Hexane: Chloroform 9:1.
5.When the solvent system reaches within 1 cm of the top of the strip, remove the strip, allow to dry at your hood workstation & view under ultraviolet light in the U.V. box. Outline the spots with a pencil by stippling around each spot while the chromatogram is still in the U.V. box.
6.Dispose of the remainder of your product into the jar provided at the front of the lab.
Infrared Spectroscopy
The natural frequencies of vibration of covalently bonded atoms correspond to radiation frequencies that lie in the infrared region of the electromagnetic spectrum. If infrared radiation is directed at an organic molecule, one of whose vibrational frequencies is the same as the frequency of the radiation, that radiation is absorbed to some degree and vibration is stimulated. The radiant energy absorbed is equal to the difference on the energies of the vibrational levels: ΔE = hv. In order for interaction with infrared radiation to occur, it is essential that the electronic dipole moment of the absorber vary during the course the vibrational motion. Thus not all vibrational modes are active in the infrared spectrum.
Particular vibrational modes (and their associated infrared absorption frequencies)
can often be identified with a specific molecular fragment. In many cases organic functional groups constitute such fragments.
Vibrational modes can be divided into two general catagories: stretching and bending modes. These modes can be further differentiated into asymmetric and symmetric stretching and rocking, scissoring, twisting and wagging, which are associated with bending.
Table of IR Absorptions
Functional Group / Characteristic Absorption(s) (cm-1) / NotesAlkyl C-H Stretch / 2950 - 2850 (m or s) / Alkane C-H bonds are fairly ubiquitous and therefore usually less useful in determining structure.
Alkenyl C-H Stretch
Alkenyl C=C Stretch / 3100 - 3010 (m)
1680 - 1620 (v) / Absorption peaks above 3000 cm-1 are frequently diagnostic of unsaturation
Alkynyl C-H Stretch
Alkynyl C=C Stretch / ~3300 (s)
2260 - 2100 (v)
Aromatic C-H Stretch
Aromatic C-H Bending
Aromatic C=C Bending / ~3030 (v)
860 - 680 (s)
1700 - 1500 (m,m)
Alcohol/Phenol O-H Stretch / 3550 - 3200 (broad, s) / See "Free vs. Hyrdogen-Bonded Hydroxyl Groups" in the Introduction to IR Spectra for more information
Carboxylic Acid O-H Stretch / 3000 - 2500 (broad, v)
Amine N-H Stretch / 3500 - 3300 (m) / Primary amines produce two N-H stretch absorptions, secondary amides only one, and tetriary none.
Nitrile C=N Stretch / 2260 - 2220 (m)
Aldehyde C=O Stretch
Ketone C=O Stretch
Ester C=O Stretch
Carboxylic Acid C=O Stretch
Amide C=O Stretch / 1740 - 1690 (s)
1750 - 1680 (s)
1750 - 1735 (s)
1780 - 1710 (s)
1690 - 1630 (s) / The carbonyl stretching absorption is one of the strongest IR absorptions, and is very useful in structure determination as one can determine both the number of carbonyl groups (assuming peaks do not overlap) but also an estimation of which types.
Amide N-H Stretch / 3700 - 3500 (m) / As with amines, an amide produces zero to two N-H absorptions depending on its type.
Nuclear Magnetic Resonance Spectroscopy ( NMR )
Unlike Infrared and Ultraviolet spectroscopy, Nuclear Magnetic Resonance Spectroscopy requires exposure of the organic substance to the radiofrequency portion of the electromagnetic spectrum while the substance is simultaneously subjected to a strong external magnetic field. Certain atomic nuclei have magnetic properties, and thus absorption or emission of energy by the nuclei may occur. The hydrogen atom is the simplest atom containing nuclei having a magnet moment. A spinning proton posses a magnetic moment which may be aligned with or against an externally applied magnetic field. Protons whose spin magnetic moments are aligned with the field are in a more stable ( lower energy ) state than those whose spin magnetic moments are antiparallel to the applied field.
Chemical Shift
Not all of the hydrogen nuclei in a molecule respond to the same degree when effected by a circulating magnetic field. We use this principle to differentiate between one type of hydrogen molecule, from one in a different location/environment. The actual location in the spectrum is arbitrarily aligned to a zero reference point – tetramethylsilane
( TMS ), which is assigned a value of 0 ppm. A mixture of an organic compound dissolved in a 5% TMS inCCl4 solution will yield an NMR spectrum where the peaks
are the hydrogen nuclei reacting to the NMR magnets magnetic field. These chemical shifts correspond to particular types ho hydrogen nuclei in their specific orientation/
environment within the molecule. The magnitude of the chemical shift depends very much upon the electron density in the area of the proton. Chemical shift tables should be used as a general guide, since combinations of effects of neighboring structures can affect
a protons shift slightly.
Spin-Spin Splitting
More complex molecules yield spectra where the total number of peaks observed is far greater than the number of different hydrogens present. The multiplicity of peaks grouped together is a consequence of the interaction of the magnetic fields associated with one type of hydrogen with those of nonequivalent neighboring hydrogens, a phenomenon known as coupling. The net effect usually is the splitting of the signal into n + 1 smaller closely spaced peaks, where n is the number of adjacent hydrogens that are equivalent to one another.
CHE-313Reporting IR and nmr spectra
Report the results of infrared and nmr spectroscopy in tabular form. See example below:
For the nmr:
1. Draw the structure of the compound and label the groups of hydrogens that give rise to each signal using a, b, c ... (let a = most up-field).
2. Make a table showing the chemical shift, integration and splitting pattern for each group of hydrogens assigned to the structure.
example: ethoxybenzene Ph-O-CH2CH3
c b a
a1.3 ppm3Htriplet
b3.9 ppm2Hquartet
c6.6-7.2 ppm5Hcomplex
For the IR:
Make a table listing in decreasing order all of the absorbances and identify those that are important.
example: ethoxybenzene
frequency (cm-)interpretation
3040C-H stretch unsaturation, Ar-H
3000
2940C-H stretch saturation
1600C=C stretch, aromatic ring
1580
1500C=C stretch, aromatic ring
1480C-H bend, saturated
1390 " " "
1300
1240
1170
1120C-O stretch, ether
1050
880
800C-H out of plane bend -
750mono-substitution
690
1
Oxidation of a side chain & introduction to IR and nmr
You will oxidize an unknown arene with KmnO4 to a benzoic acid. See the procedure in this supplement. Because the starting material is an unknown, the table of physical properties is a little different from the ones you have previously prepared. You will be given (on the unknown bottle) the molecular formula of your unknown. Calculate the gram formula weight and the number of moles contained in 1.0 grams. The amount of KMnO4 you will use is based on the formula of your unknown.
You will identify the unknown arene from the melting point of the acid product and the IR and nmr spectra of the unknown. Be sure to balance your chemical equations correctly. No mechanism is required for this report. Include the answers to the following questions in your report.
Answer the following questions:
1. Write a balanced chemical equation for the permanganate oxidation of p-xylene under basic conditions. See your general chem text for review of balancing oxidation-reduction equations.
2. Write a balanced chemical equation for the permanganate oxidation of tolune.
3. Write chemical equations to show how you would oxidize toluene to benzaldehyde rather than benzoic acid. see M&B
4. Why is benzoic acid more soluble in base than in aced?
What is this difference in solubility used for?
5. Tert-butylbenzene is not oxidized by permanganate to benzoic acid. Why not?
6. a) Draw all of the arenes with formula C7H7Br and show the products of oxidation for each one. b) Look up the mp of each product. c) Can you identify every isomer based on the melting point of the carboxylic acid derivative? Explain.
7. Write a balanced equation for the reaction of potassium permanganate with sodium bisulfite.
Identification of an unknown arene by oxidation to the carboxylic acid; introduction to IR and nmr spectroscopy.
A classical approach to the identification of some aromatic compounds is the oxidation of side chains to carboxylic acid groups. Measurement of the derivative's melting point and comparison with the known melting points of different benzoic acids provided a means of identifying or eliminating certain possible structures. For example: if a compound was found to have the formula C8H10, it could be four different compounds: ethyl benzene, o-xylene, m-xylene, or p-xylene. If you look up the boiling points of these four compounds, they are very close to each other. On the other hand, the melting points of the corresponding carboxylic acids produced from the oxidation of the side chains are distinctly different. When combined with additional information, such as the IR and nmr spectra, the melting point of the derivative will usually be sufficient to determine the structure of the unknown.
You will be given a small sample of an unknown arene for which the only information provided is the molecular formula. You are to carry out the permanganate oxidation in alkalai solution and isolate the carboxylic acid. You will measure the melting point of the acid and compare it to the melting points of the possible derivatives from your molecular formula. In addition, you will obtain the IR spectrum of your original uknown and the nmr spectrum.
procedure:
1. The apparatus consists of a 250 mL round-bottom flask fitted with a reflux condenser.
2. Place about 1 gram (40 drops) of the unknown into the flask.