Identification of Unknown Organic Compounds by Melting Point, Boiling Point and Infrared Spectroscopy PDF

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Lab 1: Identification of Unknown Organic Compounds by Melting Point, Boiling Point and Infrared Spectroscopy January 26, 2016 Methods and Background The purpose of this lab is to determine the unknown solid and liquid samples through different techniques. These techniques include the physical properties of the sample that are melting point of the solid sample K and boiling point of the liquid sample L. The Infrared spectroscopy is used to determine the number of functional groups and identify possible compound of the samples. From the elemental analysis, the molecular and empirical formulas are derived for the unknowns. Infrared (IR) Spectroscopy doesn’t provide with chemical composition or quantitative data rather it provides the peaks at certain wavenumber indicating the carbon to carbon double/triple bonds, aromatic rings, carbonyl groups, or hydroxyl groups. IR uses the wavenumber in cm-1 which provides direct relationship between energy and wavenumber and also proves the Hooke’s law. IR measures the light transmitted by the sample than absorption. The lower % transmittance, the greater is the absorption of light. The device used in this experiment is Attenuated Total Reflectance (ATR) FT-IR accessory that creates graphs with peaks indicating specific functional groups in unknown. Melting and boiling points techniques are used to figure out the physical properties of the samples. To determine the melting point of solid sample, the sample was inserted in Mel-Temp apparatus that melts the sample and determines the temperature on the thermometer. The melting point of the unknown sample is then compared to hypothetical values of other compounds that share the same physical properties. Similarly, the boiling point apparatus was set up known as miniscale method in which the liquid is boiled, and the temperature is noted on the thermometer. The results from the apparatus are then compared to other known boiling point values of compounds. Index of Hydrogen Deficiency (IHD) is used to determine the number of double/triple bonds or rings in the unknown samples. IHD values can be derived from the molecular formula. This helps us predict correct compound along with the physical properties of that compound. Experimental Procedure(s) For the melting point of solid sample K, solid sample was added in a capillary tube to the end, and the temperature was dropped to 61°C before starting the experiment. Then, the switch of the Mel-Temp device was turned on, and the capillary tube was inserted in the device. The heating level was increased frequently. The temperature was recorded when the whole sample was

melted. After recording the data, the capillary tube was disposed, and the device was switched off. For the IR of the unknowns, the surface of the apparatus was cleaned with Q-tip and acetone. Particularly, the silver disc and knob was cleaned properly. The background scan was taken and was compared to the spectrum of the standard. After matching the standard, the thin film of solid sample was placed onto the center of the disc using the Q-tip. Then, the knob was swiveled and turned to the sample so the clamp is tightly covering the solid sample. The commands were followed on the computer in order to find the peaks on the graph which was printed. Again, the disc and the knob were cleaned with Q-tip, and acetone and the black disc was placed on the middle of apparatus. The liquid sample up to five drops was added to the black disc, and the black top was covered. Again, the commands were followed on the computer to figure out the peaks on the graph of liquid sample which was printed out. For boiling point of liquid sample L, apparatus was set up and the thermometer was placed slightly above the approximated 1 ml surface of liquid in a test tube. The liquid was boiled vigorously and temperature was recorded at that time. Two trials have been done for the accuracy.

Data Acquisition/Presentation I. Relevant Equations ● Conversion of wavenumber to wavelength: Wavenumber ( cm-1) = 10,000/ λ(μm) k m∗¿ ^v = ● Hooke’s Law for simple harmonic oscillators: where: 1 √¿ 2 πc v ○ ^ = frequency of absorption in cm-1 ○ c = speed of light ○ k = force constant of bond ○ m* = reduced mass of atoms joined mAmB by bond = m A+m B ● Percent transmittance:%T = I/Io * 100 where: ○ I-intensity of radiation transmitted through sample at a particular wavelength ○ Io- intensity of radiation incident an sample at some wavelength. ● IHD from molecular formula

○ IHD = ○ IHD = ○ IHD =

(2 n+2)−x (CnHxOy) 2 (2 n+2)−( x − y ) (CnHxNy) 2 (2 n+2)−( x + y ) (CnHxXy) 2

II. Data tables Table 1. Table of Elemental Analysis and Molar Mass Unknown

Carbon (C)

Hydrogen (H) Oxygen (O)

Nitrogen (N)

Molar mass (g/mol)

K (solid)

65.31%

3.43%

21.75%

9.52%

147.032

L (liquid)

54.53%

9.15%

36.32%

0%

88.052

Table 2. Summary of Chemical Composition and Physical Properties Obtained from Calculations and Procedure Respectively Unknown

MP/BP ( °C)

Molecular Formula

IHD

K (solid)

MP- 203

C8H5NO2

7

L (liquid)

BP- 73

C4H8O2

1

Calculation: (For Solid Sample K) Molecular Formula Determination Convert percentages of elements into grams. Convert grams to moles using molecular weight. Divide all elements by lowest moles. Divide molecular weight by empirical molecular weight. Multiple that number by empirical formula to get molecular formula. 1mol = 5.438 mol = 12.01 g 1mol Hydrogen (H) = 3.43% = 3.43 g * = 3.396 mol = 1.01 g 1mol = 1.359 mol = Oxygen (O) = 21.75% = 21.75 g ¿ 16.01 g 1mol Nitrogen (N) = 9.52% = 9.52 g * = 0.680 mol = 14.01 g Carbon (C) = 65.31% = 65.31 g *

Empirical Formula- C8H5NO2 (147.16 g/mol)

5.438 mol =8 0.6 80 mol 3.396 mol =5 0.6 80 mol 1.359mol =2 0.6 80 mol 0.6 80 mol =1 0.6 80 mol

Molar mass (g/mol) = 147.032 147.16 (g/mol) / 147.032 (g/mol) = 1 Molecular Formula= 1 * (C8H5NO2) = C8H5NO2 IHD Determination: C8H5NO2 (2 n+2)−( x − y ) (2(8)+ 2 )−( 5−1 ) = 2 2

=7

Fourier Transform Infrared Spectroscopy Peaks at 3188.87 cm-1 indicates the N-H group (3300-3450 cm-1) Peaks 1724.41 and 1613.41 cm-1 indicates two C=O bonds (1750-1735 cm -1) Peaks from 1459.10 to 1329.89 cm-1 indicates benzene ring structure (1500-1400 cm-1) Hypothetical Structures Isatin

Melting Point Determination The data recorded from the experiment was 207°C Structure Elucidation The melting point of Isatin is 203 °C which is similar to the melting point of experimental data. Thus, the unknown solid sample K is Isatin.

Calculation: (For Liquid Sample L) Molecular Formula Determination Solid sample K Isatin (C8H5NO2) M.P. 203°C, 147.13 g/mol

Convert percentages of elements into grams. Convert grams to moles using molecular weight. Divide all elements by lowest moles. Divide molecular weight by empirical molecular weight. Multiple that number by empirical formula to get molecular formula. 1mol 4.54 mol = 4.54 mol = =2 12.01 g 2.26 mol 1mol 9.15 mol = 9.15mol = =4 Hydrogen (H) = 9.15% = 9.15g * 1.01 g 2.26 mol 1mol 2.26 mol Oxygen (O) = 36.32% = 36.32g * = 2.26mol = =1 16.01 g 2.26 mol Nitrogen (N) = 0 % = 0 Carbon (C) = 54.53% = 54.53g *

Empirical Formula- C2H4O (44.43 g/mol) Molar mass (g/mol) = 88.052 88.052 (g/mol) / 44.43 (g/mol) = 2 Molecular Formula= 2 * (C2H4O) = C4H8O2 IHD Determination: C4H8O2 (2 n+2)−x (2(2)+ 2)−4 = 2 2

=1

Fourier Transform Infrared Spectroscopy Peaks at 2984.33 cm-1 indicates the C-H stretching (3000-2840 cm-1) Peaks at 1736.98 cm-1 indicates one C=O bond ester (1750-1735 cm-1) Peaks at 1446.64 cm-1 indicates C-H bending (1475-1430 cm-1) Hypothetical Structures

Ethyl acetate (or)

Boiling Point Determination The data recorded from the experiment was 73°C. Structure Elucidation The boiling point of Ethyl acetate is 77 °C which is similar to the boiling point of experimental

data. Thus, the unknown liquid sample L is Ethyl acetate.

Data table using all data from the experiment: Liquid sample L UID Ethyl acetate (C4H8O2) Molecular Formula B.P. 77°C, 88.11 g/mol 8O2 IHD 7 1 Melting Point 207 °C n/a Compound

Boiling Point Structure/Name

n/a Isatin

73 °C Ethyl Acetate

Conclusion: The goal of the experiment was to determine and identify the unknown solids and liquids through different experiments such as melting point, boiling point and IR. The unknowns were solid sample K and liquid sample L which were analyzed using the IR. The molecular formula for solid sample K is C8H5NO2, and IHD is 7. Thus, after looking over the IR, the frequency at 3188.87 cm-1 indicates the N-H group (3300-3450 cm-1) in the compound. The other possible functional groups could be two C=O bonds (1750-1735 cm -1) at 1724.41 and 1613.41 cm-1. The third possible functional group in the solid sample will be Benzene ring structure (1500-1400 cm1 ) indicating peaks from 1459.10 to 1329.89 cm-1. The solid sample melted completely around 207°C which is almost identical or near to the melting point of Isatin. The melting point of Isatin is 203 °C, and the molecular formula is similar to the unknown solid sample. In the structure of Isatin, there are two rings, and five double bonds indicating IHD of 7. Thus, this indicates the unknown solid sample K is Isatin. The molecular formula for liquid sample L is (C4H8O2) and IHD is 1. Thus, after looking over the IR, the frequency at 2984.33 cm-1 indicates the C-H stretching (3000-2840 cm-1) in the compound. The other possible functional group could be one C=O bond ester (indicate the numbers) at 1736.98. The third possible functional group in the liquid sample will be C-H bending (1475-1430 cm-1) indicating peak at 1446.64cm-1. The liquid sample boiled at 75°C which is almost identical or near to the boiling point of Ethyl acetate. The boiling point of Ethyl acetate is 77 °C, and the molecular formula is similar to the unknown liquid sample. In the structure of Ethyl acetate, there is one double bond indicating IHD of l. Thus, this indicates the unknown liquid sample L is Ethyl acetate. The experiment was successful because the prediction made about the compound through molecular formula and IHD calculations matches with the data calculate from the experiments.

This means the data from the IR and melting and boiling points are helpful to determine the compound with same molecular formula and IHD. The problems that might arise with the boiling point procedure are that the level of heat should be increased if the liquid doesn’t boil. However, it did not happen to me. The reason that could cause this can be contaminated liquid sample or bad thermometer. One of the challenges that can be occurred with boiling point is that if there are not enough samples in the test tube. Reference:  

Gilbert, J.C., Experimental Organic Chemistry, Cengage Learning, Boston, 2011, 5th Ed, pp. 41, 237-256. Lenga, Robert E., eds. The Sigma-Aldrich Library Of Chemical Safety Data. [Milwaukee, Wis., USA] : Sigma-Aldrich Corp., 1988. Print....