Results from the Nmr Spectra

Vivian Chang, Jenny Chen, Mark Runyan

Lab Report No. 4

I. Introduction

In this experiment, tests and techniques used to identify extracted compounds that were unknown in the previous lab were repeated. However, application of extraction techniques was unnecessary. The lab instructor provided students with the unknown compound. In the study of organic chemistry, identification of an unknown compound through a series of experiments cannot be overstated. For instance, this lab has trained students to be trained in the capacity of IR and NMR interpretation. Secondly, it has helped establish familiarity with finding and interpreting physical properties that enables differentiation of one compound from another (i.e. boiling point, solubility, density). Lastly, it afforded the opportunity for students to "put it all together." Not only were the IR and NMR spectrum used to derive the molecular formula of the unknown; data collected on its physical properties were used to either refute or confirm the derived formula. In a world of limited resources, the ability to identify physical properties and molecular formula of an unknown compound is crucial. In addition to offering insights into what can and cannot be substituted for a desired compound, it also indicates the chemical reactions that are necessary to transform the located compound into the desired form. For this experiment, procedures used to locate physical properties of the unknown compound were available in the lab manual accompanying this experiment.

II. Experiments and Results

1. Unknown Number: 10

2. Unknown Boiling Range: 94 - 98o C

3. Density Data:

Graduated cylinder: 27.45 g.

Graduated cylinder with 10 mL distilled H2O: 37.22 g.

Temperature of water: 22o C

Graduated cylinder with 10 mL unknown liquid #10: 35.37 g.

DensityH2O at 22o C: 0.997774 g/mL1

4. Calculation of Density:

(Dunknown/DH2O @ 22o C) = (weight of 10 mL unknown/weight of 10 mL H2O)

(Dunknown/0.997774 g/mL) = [(35.37 g. - 27.45 g.)/(37.22 g. - 27.45 g.)] = 0.8088 g/mL

5. Solubility of Unknown in Various Solvents:

H2O: soluble

5% NaOH: soluble

5% NaHCO3: soluble

5% HCl: soluble

Conc. H2SO4: soluble

85% H3PO4: soluble

Ether: soluble

6. IR Spectrum

See attached documents.

7. NMR Spectrum

See attached documents.

8. Interpretation of NMR spectra

Exhibit 1: NMR Table

δ (ppm) Integral Splitting Conclusion

1.0 2.974 Triplet -CH2-CH3

2.4 2.000 Quartet -CH2-CH3

Results from the NMR spectra show a triplet near 1.0 ppm with an area of 2.974 and a quartet near 2.4 ppm with an area of 2.000. The triplet suggests that, according to the N+1 rule, there are two hydrogen atoms that are adjacent but of different types (neighbors). According to this data, it is likely that there is a - CH2 - CH3 bond in the structure of the unknown. The quartet has three "neighbors". It is likely that there is another CH3 - CH2 - bond. The data also presents the possibility of an electronegative atom in the structure of the unknown since the position of the quartet at 2.4 ppm indicates an increase in frequency and subsequently, an increase in strength of the magnetic field.

9. Interpretation of IR spectra

The IR spectra produced two significant pieces of data about the bonding nature of the structure of the unknown compound. There is a long stretch at 1716.4 cm-1, which suggests that one of several functional groups of carbonyl may be present: carboxylic acid or ketone. Also, there are intense, staggered peaks in the 2800-3000 cm-1 region, which is an indication of alkane functional groups in the structure.

10. Interpretation of Solubility Data:

All solubility tests were done on the unknown compound to observe any interaction between the unknown and solvents that may change the appearance of the solution. The unknown compound was found to be soluble in every solvent, producing clear results with no evidence of precipitate or change in appearance. The results produced determined the unknown compound to be in class S1 since the unknown compound is soluble in both water and ether. Compounds in this class are typically low in molecular weight and have 1-5 carbons in their structures.

11. Logic Leading to Proposed Identity of Unknown

In the process of identifying the unknown compound, the IR and NMR spectrum were most useful. All other tests, including that for boiling point range, density, and solubility of the compound, were used to reinforce the conclusion. Attempts to derive the molecular formula of the unknown were made, based on the IR and NMR spectrum. The former was evaluated first, followed by the latter. Long stretch at 1716.4 cm-1, along with intense, staggered peaks at the 2800-3000 cm-1 region, indicate the stretching of a C=O bond, accompanied by alkyl groups. These evidences raised the possibility that identity of the unknown was likely a ketone. This suspicion was confirmed, using the NMR spectrum. It showed a triplet with an area of 3.000 (~2.974) at a chemical shift, 1.0 ppm, as well as a quartet with an area of 2.000 at the chemical shift, 2.4 ppm. The first is indicative of 3 identical hydrogen atoms on a carbon, next to 2 identical neighbors that are different from it (-CH2-CH3). The second peak is a reiteration of the first conclusion, except that it is from the view of the -CH2-- group. It is indicative of a -CH2-- group with neighbors that are 3 identical hydrogen atoms (-CH2-CH3). Synthesis of this information leads to a molecule with:

Exhibit 2: Logic Leading to Identification

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