The purpose of lab 6’s experiment was to identify two organic compounds, one liquid and one solid, using their melting points, boiling points, Infrared Spectroscopy and proton NMR. All these tests helped to identify the unknown compounds. To start off the experiment, we determined the molecular formula using the empirical formula. A list with all the unknown compounds with the percentage of all the elements inside the compound. After we determined the molecular formula and the empirical formula, we determined the Index of Hydrogen Deficiency (IHD).
The IHD can be also unknown as the degree of unsaturation. This is an indicator of how the molecule or compound be missing hydrogen molecules to be labeled as unsaturated. The IHD helped us, in short, to determine the amount of double bonds, triple bonds or rings were present in our compound. Since we know the empirical formula and molecular formula, we know how many of each molecule there is, so such as, C, N, O and X, which is halogens.
If the IHD were a 4, we would know that the compound would have a ring structure or double bonds. The IHD helps us determine the structure better and understand where the bonds are. After determining IHD, we then proceeded to the melting points and boiling points.
We used melting point for the solid and boiling point for the liquid. The boiling and melting points not only give us a value but also tell us more about the forces. Such as, the London dispersion force. This force is the strongest out of all the bond forces. If the London dispersion force within the molecule is strong, then the melting point and boiling point will be high as well. There is a direct relationship between the two.
The reasoning for this is because since the force is stronger, more energy will be required to break these bonds up and change states (solid, liquid and gas). The two compounds had different procedures to determine the melting point and the boiling point. The liquids boiling point was determined, while the solids melting point was determined. For the boiling point, we added a boiling stone inside a small amount of the liquid and then placed it on a boiling stone with a thermometer as shown in figure 1.For the melting points, a small tube with a very small amount of solid was added then placed inside the melting point apparatus, with the help of a magnified small area, the solid was able to be seen and the temperature was able to be increased slowly so the melting point could have been written down. Multiple trials would have been done for this step because error is inevitable for any experiment but out group was unable to perform multiple trials due to time. In addition to these tests we also used a IR spectroscopy (Infrared) and HNMR spectroscopy (proton Nuclear Magnetic Resonance) to help us find and locate certain functional groups within the compound.
Both these tests helped us find these different functional groups because the IR spectra theory is that the different functional groups absorb different wave lengths(wavenumbers). This means since the functional groups absorb different wave lengths or numbers we will be able to determine certain functional groups and different wave numbers. The proton NMR was used as well. The reason we use proton NRM is because of the theory of proton NMR and that is that when certain protons are next to each other, they make a certain type of signal, the proton NMR has magnets inside. The proton NMR also depends on the nuclear spin. These certain nuclei spins are placed inside the magnetic field that will produce a certain type of magnetic field, if the molecule is next to a more electronegative atom, the signal that will be shown will be stronger peak and by pointing more down.
The number of peaks also tell us about the neighboring hydrogen atom by using this equation (number of peaks -1). This could change to number of peaks +1 if the number of coupling constants the nearest neighboring is similar and the shift in coupled nuclei constant is greater than 10. The areas of the peaks are called integrations.
Both the integration and the chemical shifts help us better understand where the hydrogens are in a compound and where we should attach each hydrogen. While performing this experiment, we faced many problems. A major problem during this lab was the amount of time we had to wait for the IR and proton NMR spectroscopy. We preformed both these tests which two lab sections, so we had a large group to cooperate with in order to start the trials and readings for both tests. Many students did not know how to use the IR spectroscopy because it was their first time using it, so they had to be taught the one TA in the room with the equipment while the other TA was observing everyone else in the lab itself.
My partner and I did not face any other problems while preforming the actual lab itself, there was no breakage of any sort during this lab. The most tough time we had was when we were asked by the TA to determine one of the structures based off its IR and proton NMR readings. This was difficult because some of the peaks were not supposed to be there but were there which cause some confusion. Our TA did help us eventually when we could not determine the compound ourselves.
Experimental Procedures Part 1: Procedure for Unknown G (solid) ? Determine the molecular formula and empirical formula of the compound using the unknowns table in the lab notebook ? Determine the IHD of the compound and see if there could be any rings present within the structure? Obtain an IR spectrum of the compound, which would give us the identification of functional groups within the structure? Obtain an Proton NMR spectrum, which would give us the amount or hydrogens attached to certain atoms and their arrangement? Using a melting point apparatus, determine the melting point of the unknown compound? Using all the information and data collected, propose one structure for either unknown compounds ? Confirm at least one structure with the TAPart 2: Procedure of Unknown H (liquid)? Determine the molecular formula and empirical formula of the compound using the unknowns table in the lab notebook ? Determine the IHD of the compound and see if there could be any rings present within the structure? Obtain an IR spectrum of the compound, which would give us the identification of functional groups within the structure? Obtain an Proton NMR spectrum of the compound, which would give us the amount of hydrogens attached to certain atoms and their arrangement? Determine the boiling point of the compound using the fume hood and a test tube attached to a thermometer? Using all the information and data collected, propose one structure for either unknown compounds ? Confirm at least one structure with the TAData CollectedEmpirical Formula and Molecular Formula: CalculationsUnknown Solid G? C- 41.65 g/12 g/mol= 3.47 molH- 2.91 g/1 g/mol= 2.91 molO- 9.25 g/16 g/mol= .58 molN- 0 g/14 g/mol= 0 molBr (X)- 46.18 g/80 g/mol= .58 mol? C- 3.47 mol/.58 mol= 6.0H-2.91 mol/.58 mol= 5.0O- .58 mol/.58 mol= 1.0N- 0 mol/.58 mol= 0