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Lee 1 Sarah Lee (UIN: 670332154) CHEM 233 - McQuade 19 June 2014 Lab 1: Identification of Unknown Organic Compounds by MP, BP, and Infrared Spectroscopy I. Methods and Background The objective of this lab was to use various methods to identify an unknown organic liquid and unknown organic solid and to determine their chemical structures. One of the methods was elemental analysis, which was used to find the molecular formula of each unknown organic compound. Another important method was calculating the index of hydrogen deficiency (IHD) in order to determine the number of double bonds or rings in the compound. Infrared spectroscopy (IR spectroscopy) was implemented to determine the functional groups of the unknowns. Additionally, finding the melting point of the solid and the boiling point of the liquid was necessary to determine the final identities of the unknown organic compounds. Ultimately, the objective of the lab reveals a variety of ways to deduce an organic compound by determining its molecular formula, number of double bonds or rings, functional groups present, and either the boiling point or melting point. Elemental analysis is a method to determine the empirical and molecular formula through calculations. This calculation requires using the percentages of the elements in the compound as well a their molecular mass. Since this information was provided for the lab, elemental analysis could be used to find the molecular formulas for the organic compounds. Elemental analysis starts by solving for the empirical formula, a formula written in which the coefficients of the elements are written in their simplest integer ratio. To do this, the percentages of the elements in the compound are assumed as grams (totaling to a theoretical 100 grams of the compound total) and then are converted to moles by using molar mass. After being converted into moles, the calculations are normalized by dividing by the smallest number of moles. This results in a number ratio that acts as the coefficients for the compounds. If the numbers are not integer values, they may be multiplied out to become a whole integer. From the empirical formula found, the molecular mass that was given can be used to solve for the molecular formula, which is important to know for determining the unknown organic compounds because it reveals what elements are in the compound and how many moles of each compound exists. Index of hydrogen deficiency (IHD) calculation determines the number of double bonds, triple bonds, or rings in a compound. This is useful in determining the structure of a compound. To find the IHD, the number of carbons, hydrogen, nitrogen, and halogens are taken into consideration in a specific equation. However it must be noted that while IHD provides insight on the structure of the organic compound, it does not differentiate between cyclic systems and double bonds; the IHD number simply indicates the presence of double bonds, triple bonds, or rings. Still, the IHD is still helpful in generalizing

Lee 2 possible structures for the unknown organic compound. The IHD is calculated by the equation: 𝐼𝐻𝐷 =

2𝐶 + 2 − 𝐻 − 𝑋 + 𝑁 2

The variables C, H, X, and N (used above) refer to the number of carbon, hydrogen, halogen, and nitrogen in a compound respectively. Determining the melting point for a solid or the boiling point for a liquid is another required step to figuring out the unknown compounds. Some compounds may have the same molecular formulas as another, so knowing the melting or boiling point is necessary because compounds with the same molecular formula are arranged in completely different ways, which would greatly change the phase transition temperatures. As a result, many compounds with the same molecular formula can be differentiated through boiling point or melting point. The melting point of a compound is found by heating a solid until it liquefies. The boiling point of a compound is found by heating a liquid until it boils at a constant temperature. Some challenges presented with this method are that some compounds have similar boiling points or melting points, making differentiation between them difficult. In addition, the presence of impurities in compound samples can change the boiling point or melting point and yield an invalid value. Performing more than one trial can provide more accurate temperature values for the boiling point or melting point. Finally, IR spectroscopy helps determine the functional groups of a compound. This is used to further deduce the correct structure of a compound once its molecular formula is known. IR spectroscopy is used to measure transitions among different molecular vibrational-rotational levels (Gilbert 234). Furthermore, it can be said that IR radiation affects an organic molecule by “stretching” the covalent bonds between atoms much like a spring (Gilbert 236). Thus IR radiation corresponds with the vibrational states of molecules through specific stretches or bending. Thus, this atomic stretching can be compared to Hooke’s Law for simple harmonic oscillators (Gilbert 228). The equation for Hooke’s Law is: 𝜈=

1 ∗ 2𝜋𝑐

𝑘(𝑚! + 𝑚! ) 𝑚! ∗ 𝑚!

The variable v (with a tilde) represents the wavenumber (in cm-1), the c represents the speed of light, the k represents the force constant of the bond that is measured, and ma and mb represent the reduced mass of atoms joined by the bond (Gilbert 236). As a result of this equation, the different energies that are needed to cause molecular vibrations associated with certain types of bonds can be determined (Gilbert 237). The many different energies that result from these vibration frequencies correlate with certain functional groups, which is what IR absorptions ultimately measure. Dipole moments associated with vibrations are reasons why some functional groups yield stronger absorptions as well as why we can use IR can measure them. The vibrational energies are absorbed in FT-IR instruments through infrared radiation, which measure light that has

Lee 3 been transmitted through the sample, known as transmittance (Gilbert 229). Infrared spectra are measured by an incident radiation versus transmittance plot. The lower percentage of transmittance indicates a higher amount of incident radiation (expressed as the wave numbers). A strong absorption would thus be reflected by a peak, and the energy to produce thee peaks would decrease from left to right (Gilbert 230). The approximate range of absorptions in the 4000-1250 cm-1 range is the functional group region where vibrations of these functional groups are measured (Gilbert 238). By reading measurements on IR spectroscopy, the functional groups for these unknown organic compounds can be found and be used to help determine the identities of these compounds. In this lab, an FT-IR instrument is used. This device uses ATR spectra (a means to obtain an IR spectra through the FT-IR spectrum) (Gilbert 237). The challenge to using IR spectroscopy is to figure out where the functional groups are on the reading and what types of functional groups they represent.

Figure 0 IR Spectra Example (does not correlate with actual findings)

Above, Figure 0 is an example of IR spectra and shows some of the few functional group stretches, such as the –OH stretch at approximately 3600-3400 cm-1 and the C-H alkane stretches from 2850-2970 cm-1. IR spectroscopy provides data on the functional groups present in unknown compounds, but the measurements require close inspection. For instance, the fingerprint region from 1250-500 cm-1 is not practical to read because of the large number of bands that appear in that region (Gilbert 250). The overall conclusions of this lab are found through the methods described above. Elemental analysis will provide molecular formulas while the IHD is determined by calculation. Running an IR spectra will show which the functional groups present or absent in the organic compounds, which will allow hypothetical structures to be formulated with the information gathered. Finally, melting point and boiling points will be used to determine the correct actual structures and identities of the unknown compounds.

Lee 4 II. Experimental Procedures Given the table of unknown compounds as provided by the lab manual, the assigned unknown compounds (solid M and liquid N) were observed for the percentage of elements and molecular mass. Then, elemental analysis was used to find the empirical formula and molecular formula. This was done by first converting the percent by composition of each element into mass (in grams) and then converting those values into moles. The subsequent molar values were divided by the smallest number of moles in order to attain a normalized empirical formula. To properly calculate the molecular formula for unknown organic solid M, the number of moles for each element was multiplied by a factor of 3 in order to reach integral coefficients for the empirical formula. Afterwards, a ratio between the molecular weights for both the molecular formula and the empirical formula was conducted. For both compounds M and N, there was a 1:1 ratio between the molecular and empirical formula in terms of molecular weight. Thus, the molecular formulas for M and N were the same as their empirical formulas. Next, IHD calculations were performed in order to deduce the number of double bonds, triple bonds, or rings in compounds M and N. Since all compounds only contained carbon, hydrogen, and oxygen, the IHD equation was be modified to become: 2𝐶 + 2 − 𝐻 2 The variables C and H refer to the number of carbon and hydrogen in a compound. The IHD was calculated for both M and N. 𝐼𝐻𝐷 =

Next, samples of both compounds underwent IR spectroscopy in order to determine the functional groups that were present. Before any sample was placed in the IR machine, a background scan was completed in order to ensure that the machine was working properly. After this was done, a sample space on the IR was cleaned using a Q-tip with acetone. Then, a drop of the unknown liquid compound N was placed on the IR machine and a scan was conducted. The IR spectrum for compound N was displayed on the computer screen and was printed out. Then, the sample space was once again cleaned and prepared with a Q-tip with acetone, and another background scan was conducted. Next, a sample of the unknown solid compound M was placed on the sample space and scanned. The IR spectrum for compound M was displayed on the computer screen and this graph was printed out. After the IR spectra for each compound were acquired, the functional groups for each compound were recorded and potential structures for the compounds were predicted. Finally, to figure out the correct structures, the boiling point for the unknown liquid and the melting point for the unknown solid were ascertained. To find the boiling point for compound N, a heating apparatus was set up to use the miniscale approach (Gilbert 41). First, approximately 1 mL of compound N was added to a test tube, which was then clamped to a stand attached to a heating apparatus. The test tube rested slightly above a heating area, and a thermometer was also clamped to the stand and placed in the test tube;

Lee 5 the thermometer was carefully placed so that it was suspended just above the liquid. A boiling stone was also placed in the test tube. Next, the heating apparatus was turned to 40° C, and the liquid was heated consistently until it was bubbling and giving off vapor. This temperature was recorded at this time. This procedure was repeated again for a second trial in order to get a more accurate boiling point, this time heating more slowly at about 1-2° C rise per minute. Next, to obtain the melting point for the unknown organic solid M, a small sample of the M was placed in a watch glass. A small amount of this sample (1-2 centimeters) was packed into a capillary tube. The capillary tube with the solid substance was then placed in a drop tube in a heating device that would melt the solid while the temperature was being measured. For the first trial, the solid compound was heated rapidly in order to obtain an approximate melting point. For the second trial, the previous steps were repeated, but the solid was heated at a slower pace in order to acquire a more precise temperature range. Melting point was recorded when the solid liquefied. After the boiling point of N and the melting point of M were recorded, these values were compared in the Aldrich Index. As a result, the compounds were identified based on their molecular formulas, IHD, IR spectrum, and melting/boiling point. Final structures and formulas of the organic compounds were recorded. III. Data Acquisition The data was acquired through various methods that included: elemental analysis, IHD determination, IR spectroscopy, and melting point/boiling point determination. Elemental analysis helped determine the molecular formula by analyzing percentages of elements and using molar mass. IHD determination was used to predict the structures by knowing the number of double bonds, triple bonds, or rings that would have to exist in the compounds. IR spectroscopy was used to show which functional groups were present in the compounds. Finally, melting/boiling point measurements were used to eliminate incorrect structures that had the same molecular formula and subsequently identify the correct ones. Table 1: Unknowns- Table of Elemental Analysis and Molar Mass for M & N Unknown

Carbon (C)

M (Solid) N (Liquid)

63.15% 69.72%

Hydrogen (H) 5.30% 11.70%

Oxygen (O) Nitrogen (N) 31.55% 18.58%

Molecular Formula Determination with Elemental Analysis: Unknown Organic Solid M C:

63.15 𝑔 𝐶

12.01 𝑔/𝑚𝑜𝑙 = 5.258 𝑚𝑜𝑙 𝐶

0% 0%

Molar Mass (g/mol) 152.047 86.073

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H:

5.30 𝑔 𝐻

1.01 𝑔/𝑚𝑜𝑙 = 5.248 𝑚𝑜𝑙 𝐻

31.55 𝑔 𝑂 O: 16.00 𝑔/𝑚𝑜𝑙 = 1.972 𝑚𝑜𝑙 𝑂 C: 5.258 mol C / 1.972 mol = 2.667 * 3 ≈ 8 H: 5.248 mol H/ 1.972 mol = 2.661 * 3 ≈ 8 O: 1.972 mol O/ 1.972 mol = 1 * 3 ≈ 3 Empirical Formula: C8H8O3 Empirical Weight: (8 * 12.01) + (8 * 1.01) + (3 * 16) = 152.16 g/mol Ratio of Molecular and Empirical: 152.047 g/mol / 152.16 g/mol ≈ 1 Molecular Formula: C8H8O3 Unknown Organic Liquid N C:

69.72 𝑔 𝐶

12.01 𝑔/𝑚𝑜𝑙 = 5.805 𝑚𝑜𝑙 𝐶

11.70 𝑔 𝐻 H: 1.01 𝑔/𝑚𝑜𝑙 = 11.58 𝑚𝑜𝑙 𝐻 18.58 𝑔 𝑂 O: 16.00 𝑔/𝑚𝑜𝑙 = 1.161 𝑚𝑜𝑙 𝑂 C: 5.805 mol C / 1.161 mol ≈ 5 H: 11.58 mol H/ 1.161 mol ≈ 10 O: 1.161 mol O/ 1.161 mol ≈ 1 Empirical Formula: C5H10O Empirical Weight: (5 * 12.01) + (10 * 1.01) + (1 * 16) = 86.16 g/mol Ratio of Molecular and Empirical: 86.073 g/ mol / 86.16 g/mol ≈ 1 Molecular Formula: C5H10O IHD Determination: Unknown Organic Solid M: C8H8O3 𝐼𝐻𝐷 =

!(!)!!!!!!!! !

= 𝟓 double bonds or triple bonds or rings in this compound

Unknown Organic Liquid N – C5H10O 𝐼𝐻𝐷 =

!(!)!!!!"!!!! !

= 𝟏 double bond or triple bond or ring in this compound

Lee 7 Tables 2 + 3: FT-IR Spectrum Data for Unknown Organic Compounds Unknown organic solid M Wavenumber (cm-1) 2857.45 1241.59 1575.32

Functional Group Aldehyde (C-H stretch) Carboxylic Acid C=C aromatic

Unknown organic liquid N Wavenumber (cm-1)

Functional Group

2971.65

C-H stretch

1712.63

Aldehyde

1358.14

C-H bond

Figure'1:'FTIR'Spectra'for'Unknown'Compound'M'(attached'on'back)' ' Figure'2:'FTIR'Spectra'for'Unknown'Compound'N'(attached'on'back)' ' Figure'3:'Proposed'Structures'for'Unknown'Organic'Compounds'(below):' ! ! Unknown!Organic!Solid!M!Possibility:! ! !!!!!!!!!4-menthoxybenzoic!acid! ! ! ! ! ! ! ! ! ! Unknown!Organic!Liquid!N!Possibilities:! !!!!!!!!!!3-methylbutan-2-one! ! ! ! 3-methylbutyraldehyde! ! !! ! ! ! ! ! !

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Table 4: Boiling Point/Melting Point Table Unknown Compound

Unknown Solid M (C8H8O3) Unknown Liquid N (C5H10O)

Experimental Melting/Boiling Point (° C) 178.8°C

Theoretical Melting/Boiling Point (° C) 92°C

89°C

184°C

IV. Conclusion The purpose of this lab was to determine the structure and identity of an unknown organic solid and an unknown organic liquid. To deduce the molecular formula and structure of these organic compounds, various methods were used including elemental analysis, IHD determination, IR spectroscopy, and melting point/boiling point determination. Through a combination of all these methods, it can be determined that unknown solid M is 4-menthoxybenzoic acid, and the unknown liquid N is 3methylbutyraldehyde. These structures are shown below. Therefore, the purpose was achieved because both compounds were identified successfully in the lab. Solid Organic Compound M: 4-menthoxybenzoic acid

Liquid Organic Compound N: 3-methylbutyraldehyde

Determination of the molecular formula was conducted using the information in Table 1. The empirical formula of unknown liquid N was calculated using the steps listed under the “Molecular Formula Determination with Elemental Analysis” section. The formula was C5H10O and had a 1:1 ratio in terms of molecular weight with the molecular weight given in chart in the lab manual. While the empirical formula of solid M was calculated with the same steps, the formula was not all in integral numbers and as such had to be multiplied by a factor of 3. This yielded the empirical formula for unknown solid M to be C8H8O3, which also had a 1:1 ratio of molecular weight to empirical weight. Therefore, the molecular formula of liquid N is C5H10O, while the molecular formula of solid M is C8H8O3.

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After the molecular formulas were determined, IHD was calculated for both compounds. The results of the calculation showed that the liquid organic compound had an IHD of 1, and the solid organic compound had an IHD of 5. This would suggest that the liquid sample would have either 1 double bond or 1 ring, while the solid sample could have 5 double bonds and/or rings. Also, it was noted that compounds with an IHD of 4 or greater are much more likely to have a benzene ring; thus, it was strongly suggested by the IHD number of 5 of that the solid organic compound would involve a benzene ring in its structure. Though the IHD numbers did elucidate some of the structures for the organic compounds, there was still not enough data to identify the compounds. Next, IR spectroscopy was collected for both liquid and solid compounds. For the organic solid M the peak at 2857.45 cm-1 is indicative of an aldehyde. This is because a peak between the region of 2830-2695 cm-1 indicates the C-H stretch of an aldehyde. Additionally, the 1241.50 cm-1 peak indicates the presence of a carboxylic acid because this value falls in the range for the C-O stretch of a carboxylic acid (1320-1210 cm-1). Finally, the peak of 1575.32 cm-1 indicates a C-C stretch in an aromatic ring. Thus, this validates former predictions that were made from the high IHD number of 5 that suggested that the solid organic compound would have a ring structure. As a result of these perceived IR functional groups, one predicted structure was made to be 4menthoxybenzoic acid because this structure is a ring structure with an aldehyde and carboxylic acid and has a total IHD number of 5 (four double bonds and one ring structure). This structure also matches the molecular formula that was deduced, C8H8O3. For the liquid organic compound, there was a peak at 2971.65 cm-1 that suggested a C-H stretch in the compound. In addition, there was a peak at 1712.63 cm-1 that indicates the presence of an aldehyde in the structure. Finally, the peak at 1358.14 cm-1 indicates a C-H bond. As a result and taking into consideration the molecular formula of C5H10O, two hypothetical structures were proposed, 3-methylbutan-2-one and 3-methylbutyraldehyde. Although both follow the correct molecular formula, it was predicted that the latter would be more likely the correct structure for compound N because it contains an aldehyde, like the IR spectra...