Mystery Molecule Report

Mystery Molecule Report

March 9, 2011

Michelle

Jen N

Jen S

Introduction

For this experiment we were given an unknown substance and were assigned to determine its molecular structure by running appropriate chemical tests as well as performing an Infrared Spectrum analysis and an H-NMR analysis. We were given the Mass Spectrum data for our unknown to analyze as well. We used the book Introduction to organic laboratory techniques: a microscale approach By Pavia, for directions on how to perform the chemical tests, and Organic Chemistry by McMurry for deciphering the graphs from computer analysis, as well as various handouts given in class.

Chemical Tests

We began by classifying the given molecule by physical state, color, and odor. Its physical state at room temperature is a white crystalline solid, with a slight yellow tinge. When it was held it in its container in a warm hand the crystals began to stick together. Since our sample was a solid we did a melting point test. We filled a capillary tube with the unknown substance to about 3 millimeters and dropping the capillary tube through a roughly 2 foot long piece of glass tubing with the open end up, in order to get the crystals to the bottom of the capillary tube. The capillary tube was then placed in a melting point apparatus, open end up, and the heat was turned up by gradually turning the dial. One person looked through the magnifying glass to observe when the crystals would melt, and another person observed the thermometer. The crystals began to melt at 34°C and were completely liquid at 39°C.

Then we performed the Solubility Test. We first found it to be predominantly insoluble in water, soluble in sodium hydroxide, and insoluble in sodium bicarbonate. We began performing chemical test based on these results thinking perhaps we had a phenol, diketone, or diester. After examining our results from the IR, NMR, and mass spectroscopy we began to doubt the accuracy of this result and performed the sodium bicarbonate test a second time, finding that although it did take almost an hour it was actually soluble in it, and looked toward the possibility of it being a carboxylic acid.

The Beilstein test for halogen confirmation was also performed. For the Beilstein test we hooked up a Bunsen burner to the gas outtake, turned the valve on and applied sparks to the open end of the Bunsen burner with a flint lighter and adjusted the flame so that it was blue. We then bent a piece of copper wire to make a little loop at the end and heated the loop up in the flame untill it glowed bright golden. Then we let it cool before wetting it in distilled water on a watchglass in order to get our solid sample to stick to the copper wire. Both initially were positive indications; we observed only a flash of green flame. However, a second run of the Beilstein actually indicated a negative result. The second time running the Beilstein we also tested a molecule we know should test positive for a halogen, bromobenzene, and observed a long green flame. We also tested a molecule that should test negative for a halogen, benzoic acid, and no green flame was observed when it was tested. The false positive result that initially occurred could possibly have been from using tap water instead of distilled water, or perhaps the watchglass was dirty. The second attempt with our sample no green was observed at all. This indicates we do not have a halogen in our sample.

Based on our initial faulty interpretation of the solubility and Beilstein tests we then tested for phenols by dissolving our sample in 10% NaOH, and also the NaI in acetone, both proved negative raising doubts of our idea. The 10% NaOH if positive would show a red or yellow color due to the anion of the phenol, which did not occur when we dissolved our sample. This negative does not rule out a phenol however. The NaI in acetone combined with our sample dissolved in ethanol, did not produce any cloudiness or precipitate as it would with a bromide or a chloride. This confused us based on our initial positive Beilstein result, but does actually align with our proposed molecule, as there is no bromine or chlorine present.

We tested for simple multiple bonds with the Bromine in Methylene Chloride test by first dissolving 50mg of our unknown in 1mL of methylene chloride. We then added 2% by volume solution of bromine in methylene chloride, one drop at a time, while shaking the test tube. The yellow-orange color was not discharged. Though we have double bonds in our proposed conclusion they are part of an aromatic which will not give a positive result, not reacting or possibly reacting with the bromine through substitution, so our result was negative.

The Ignition test for the possibility of a high degree of unsaturation was performed twice. We did this under the fume hood, setting up a Bunsen burner and placing a small amount of our sample on the end of a spatula into the flame. The first time demonstrated what could be described as a sooty flame. This positive result would indicate a high degree of unsaturation, possibly an aromatic. The second time the test was done soot was not observed. We decided that this test was inconclusive in discovering the structure of the molecule.

The Ferric hydroxamate test was used to determine the presence of an ester. A few crystals were dissolved in 1mL of 95% ethanol. 1mL of 1.5M hydrochloric acid was added, then two drops of 5% ferric chloride solution was added. The solution turned a bright transparent yellow, showing no enolic character. We then dissolved 40mg of our unknown solid in a mixture of 1mL of 0.5M hydroxylamine hydrochloride dissolved in 95% ethanol and 0.4mL of 6M sodium hydroxide. The mixture was heated to a boil for a few minutes and left to cool. Once it was cooled to near room temperature, 2mL of 1M hydrochloric acid was added. The solution was cloudy so we then added 95% ethanol to clarify the solution. Drops of 5% ferric chloride solution was then added and it became an opaque muddy brown color.

 
We performed the pH test of an aqueous solution which tested for carboxylic acids. We dissolved our sample in ethanol, then added water until the solution just begins to become cloudy, and clarified the solution by adding more ethanol a drop at a time. We then tested the pH of this solution. Our sample indicated a pH between 3.5 and 4. We did the same test on benzoic acid and a 5% sodium bicarbonate solution. The benzoic acid tested around a pH of 3.5-4.0 and the sodium bicarbonate tested at a pH of 8. This test shows that our unknown has the same pH as benzoic acid.

When we changed our assumption to carboxylic acids as a possible group we dissolved our sample in 5% aqueous sodium bicarbonate and observed a definite bubbling of carbon dioxide. To confirm our positive result we then repeated this with benzoic acid and observed a similar bubbling. This was a positive chemical test indicating we did indeed have a carboxylic acid, as we believe we do. This test was also performed on potassium iodide, which tested negative for carboxylic acid, as suspected. The potassium iodide did not bubble and sunk to the bottom of the test tube, where the two positive tests floated near the top of the liquids surface.

Due to our IR showing a strong peak at 1690, indicating a carbonyl we performed the 2,4 dinitrophenylhydrazine test. A positive would indicate a ketone or aldehyde. When our sample was dissolved in ethanol and then combined with the test substance we did not observe any precipitate during the 15 minutes interval. This negative result aligns with our proposed identity, we do have a carbonyl, but it is part of a carboxylic acid.

 

Analysis of Spectral Data 

Though the IR we ran on our sample was indeterminate in the 3000cm-1 area, we did have a sharp peak at 1690cm-1 which indicates a carbonyl group, Referring to our IR there is a broad O-H stretch between 2500 and 3200, which is referenced as the O-H from a carboxylic acid. This region on our IR taken being weak may be due to how solids do not give as accurate of a reading as liquids do. The peaks at 1298 and 1213 indicate a C-O from the carboxylic acid group.

 IR spec taken of sample

Our IR was compared to the IR from the Spectral Database for Organic Compounds, SDBS online for hydrocinnamic acid, which does have peak information, and provides more detail than the sample we ran. Concerning the aromatic portion of our molecule this IR shows peaks at 1603, 1584, 1501, and 1498. These correspond with those referenced for a mono substituted aromatic. Also peaks at 775, 703, and 675 are within the range of a mono substituted aromatic.

IR spec from Spectral Database for Organic Compounds SDBS

The Mass Spectrum of our sample was given to us by our instructor. It showed a molecular weight of 150g/mol for our ion. Hydrocinnamic acid's molecular weight is 150.17g/mol. The even number demonstrates an even number of Nitrogen, we believe we have zero. The is no M+2 peak to indicate a bromine or chlorine. The next molecular ion peak is at 105 g/mol, this corresponds to the carboxylic acid group falling off, as it has a molecular weight of 45g/mol. There is an ion at 91g/mol, 14 less than the last peak indicating a -CH2 was removed. From that point the molecule continues to break off in chunks of -CH2 groups.

 Mass Spectrum of sample

The first clue on our proton NMR we deciphered was there being an isolated, deshielded H shifted far downfield at 10. 6 ppm. Assuming that represented a single H we were able to look at the integration numbers to estimate there being 4-5 H's at the single 7.2 ppm peak, and 3-4 represented at the indecipherable number of peaks in the 2.5-3.1 ppm area. This agrees with hydrocinnamic acid in that the carboxylic group, H would indeed be very deshielded by the oxygens, and appear at the far downfield end of the spectrum between 10-13 ppm. The five aromatic H's are equivalent and therefore do not split the signal. The peak's 7.2 ppm placement also agrees with the approximate value of an aromatic H as being between 6.5-8ppm. Though a second degree alkyl H with shielding would have a value of 1.2-1.4ppm, our two -CH2 groups are both deshielded to a degree by the aromatic on one side and the carbonyl of carboxylic acid on the other with respective approximate values of 2.3-2.7, and 2.1-2.5. The splitting occurs because these are not equivalent due to the different R groups on either side. We would expect to see two triplets, due to the n+1 rule.

H-NMR taken of sample

Our carbon 13 NMR from PLU demonstrates 7 different kinds of carbons, though hydrocinnamic acid has 9 carbons, there are two pairs of equivalent carbons on the aromatic ring due to the symmetry plane leading to only 7 peaks. We have the furthest downfield 179.70ppm peak, within the reported range of our carbonyl carbon. The 4 peaks between 126ppm and 140ppm are within the range of the aromatic we have. Lastly the most shielded and upfield two peaks at 35 and 30ppm are within the reported range of a CH2.

13C-NMR from Pacific Lutheran University

Our conclusion is that our sample is hydrocinnamic acid, also known as 3-phenylpropionic acid, molecular formula C9H10O2. Our sample is a solid at room temperature, white colored and flaky textured. It did not have a strong aroma to us, just a mild odor. These descriptions do align with those of hydrocinnamic acid, though additionally it has been described as having a floral scent, none of us were able to pick up the floral smell. It is used as a food additive for its aroma. Our melting point also aligns with our proposal. According to Sigma-Aldrich the melting point of hydrocinnamic acid is 45-48C. Our sample began to melt at 40C completed at 46C and recrystallized at 44C. The pH of hydrocinnamic acid was not found anywhere online so we didn’t have a comparative number for analysis.

References


Pavia, D. L., Lampman, G. M., Kriz, G. S., Engel, R. G. (2007), Introduction to organic laboratory techniques: a microscale approach. United States: Brooks/Cole, Fourth edition.

McMurry, J., (2008), Organic Chemistry. United States: Brooks/Cole, Seventh Edition.

Spectral Database for Organic Compounds SDBS, http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi

Sigma-Aldrich MSDS http://www.sigmaaldrich.com