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Maha Haroon Xuan Duong Chem 233 CRN:18713 02/25/2021 Pre-Lab Report: Organic Chemistry 1, Lab 5:Determination of Unknown Organic Solids & Liquids by Elemental Analysis, Melting Point, Boiling Point, and Spectroscopy (Infrared & Nuclear Magnetic Resonance

● Introduction In this lab, we will be identifying the structure of an unknown organic compound (unknown solid and unknown liquid). We will be able to identify the unknown compounds by using different methods and techniques.. We will be using the empirical formula, the molecular formula, the index hydrogen frequency (IHD), the infrared spectroscopy (IR), the nuclear magnetic resonance spectroscopy (NMR), the melting point of the unknown solid and the boiling point of the unknown liquid. After obtaining and analyzing the techniques used, we will be able to identify the unknown compounds Melting point of any substance tells a significant amount of information about the compound, more importantly, in a solid compound.The melting point can tell us the range of the temperature time/change it takes from going from a solid into a liquid. These ranges of temperature changes are extremely important, because we know that pure substances/compounds have a small melting range, while impure substances have a larger melting range. Being able to identify the melting point of the unknown solid will help us identify if that unknown substance is a pure substance or not. For the unknown liquid, we will be able to identify it by its boiling point. In our previous experiments, we identified boiling points as a measure of their vapor pressure, the liquid substance changing into a vapor/gas like substance. We would be able to tell that the liquid is boiling when we see bubbles forming. After reaching its boiling point, it will remain in that temperature range until the substance is vaporized. That temperature point is important for us to understand the vapor pressure of the substance. If there's a higher liquid altitude, there would be a higher boiling point. If the liquid has a smaller altitude, it will have a smaller boiling point. In previous experiments, we also saw that the boiling point also determines if the substance/compound is polar or nonpolar. The higher the boiling point, the more polar the substance is, and vice versa. Besides using the boiling point and melting point to determine the unknown substances given to us, we will be using Infrared spectroscopy. In a previous experiment, we saw how quickly the results of this method give us. Organic chemists use this tool to determine and analyze the peaks that correspond to the functional groups that are present in the spectrum. The peaks will represent the purity of the substance. When a compound is placed under the IR, it absorbs energy, which gives us the wavelength of the compound. The frequencies that are represented in the IR spectrum will give us the functional groups present in the substance. Another type of spectroscopy, Nuclear Magnetic Resonance Spectroscopy, will also be helpful in identifying the unknown organic compounds. We use the NMR to analyze and identify the carbon and hydrogen atoms in the compound, which is different from the IR spectroscopy, which identifies the functional group of the compound. Besides that, we will also be using the IHD formula to determine the degrees of saturation, more importantly, how many bonds or rings are within the compound. We will also be using the empirical formula, which tells us the percent composition of each of the unknown

compounds. Once the empirical formula is calculated, we will be able to determine the molecular formula, which will tell us the type of atom in each of the unknown compounds. With all of these techniques, we will be able to understand the unknown solid and liquid compounds that are given to us.

● Procedure -

Unknown Organic Liquid

1. Molecular Formula Determination: using the molecular weight and the elemental analysis from the table, determine the empirical formula and molecular formula of the unknown liquid provided. Show calculations 2. IHD determination: Find the IHD of the unknown liquid to determine the number of possible combinations, such as: double bonds, triple bonds, or rings. Show calculations 3. Fourier Transform Infrared Spectroscopy: Obtain the spectrum from the attenuated total reflectance (ATR) accessory. Identity three characteristic stretches, and list the functional groups vibrations. At this point, draw a hypothetical structure 4. Nuclear Magnetic Resonance Spectroscopy: Obtain a NMR spectrum and identify and record the chemical shift, multiplicity, and the integration of each peak observed. After identifying the NMR, draw the proposed structure 5. Boiling point Determination: Determine the boiling point of the unknown liquid, using the summarized version in the pre-lab slides for this lab. 6. Find the proposed structure of the unknown liquid compound, compare its boiling point to one obtained. If the proposed structure boiling point does not match with the the liquids boiling point, revisit calculations and redraw the the hypothetical structure

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Unknown Organic Solid

1. Molecular Formula Determination: using the molecular weight and the elemental analysis from the table, determine the empirical formula and molecular formula of the unknown solid provided. Show calculations 2. IHD determination: Find the IHD of the unknown liquid to determine the number of possible combinations, such as: double bonds, triple bonds, or rings. Show calculations 3. Fourier Transform Infrared Spectroscopy: Obtain the spectrum from the attenuated total reflectance (ATR) accessory. Identity three characteristic stretches, and list the functional groups vibrations. At this point, draw a hypothetical structure 4. Nuclear Magnetic Resonance Spectroscopy: Obtain a NMR spectrum and identify and record the chemical shift, multiplicity, and the integration of each peak observed. After identifying the NMR, draw the proposed structure 5. Melting point Determination: Determine the melting point of the unknown solid, using the melting point apparatus. 6. Find the proposed structure of the unknown solid compound, compare its melting point to one obtained. If the proposed structure melting point does not match with the the solids melting point, revisit calculations and redraw the the hypothetical structure

● Equations/Calculations for reactions -

Determine the Empirical and Molecular Formula

IHD Formula

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IR Spectroscopy (Example)

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NMR Spectrum (Example)

● Pre-Lab Questions: 1. Why is it important to consider molecular weight in addition to elemental analysis when determining molecular formula? In elemental analysis, molecular weight is important because after elemental analysis, we can only get an empirical formula of the compound. To determine the exact molecular formula, we need molecular mass to be divided by empirical formula mass. So in hindsight, the importance of molar mass is mandatory

2. What does “index of hydrogen deficiency” mean? What are we calculating with these equations? Index of Hydrogen Deficiency is defined as: The number of hydrogen required to become the compound fully saturated. It also helps in determining the degree of unsaturation present in the compound, more importantly, if the compound has any rings or multiple bonds involved.

3. What structural information can we gather from IR spectroscopy? Can IR alone determine the structure of a molecule? IR Spectroscopy plays a huge role in analyzing and identifying the functional groups present in the compound. The IR spectra alone can’t really determine the complete structure, it can only predict the functional groups present in the compound.

4. What structural information can we gather from NMR spectroscopy? Can NMR alone determine the structure of a molecule? The NMR spectra determines the complete structure of an organic compound. It gives us information regarding the number hydrogen atoms, flueron atoms, phosphorus atoms, etc. It can also tell you the multiplicity of the NMR atoms. By integration you can get the number of protons. By coupling constant and splitting patterns you can see an environment of protons. Overall by NMR you will come to know the structure of the organic compound.

5. There are eight compounds but only four infrared spectra. Match each spectrum below to their respective molecules by placing the numbers for each structure in the circles to each spectrum....