CA3- Ans Key

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Feb 20, 2024

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Start: 1. If the compounds listed below are run on a non-polar GC column, which compound will have the highest retention time tR? Compound Boiling point - (°C) A. 1,1-dimethylcyclohexane 132 B. Pentane 36 C. Octane 126 D. 2,3-Dimethyl octane 165 E. Heptane 98 The reaction of benzene [1.50 g] with 1-chloropropane [1.50 g] in the presence of AlCl 3 yields [1.35 g] product which was subjected to GC analysis equipped with a thermal conductivity detector (TCD). The chromatogram was recorded on a chart recorder with paper fed at a rate of 100 mm per minute. A mark was made on the chart when the sample was injected. [q2-q4] 2. The first peak on the chromatogram (identified as n-propyl benzene) was observed at a distance of 5.11 cm from the injection point marked on the chart and the second peak (identified as isopropyl benzene) was observed at a distance of 7.88 cm from the injection point. What was the retention time for n-propyl benzene (in seconds)? A. 35.87 B. 51.10 C. 47.28 D. 30.66 E. 78.80 3. The areas of the two peaks on the chromatogram were - n-propyl benzene [area = 64 mm 2 , Wf -1.09] and isopropyl benzene [area = 115 mm 2 , Wf -1.04]. Calculate the amount in grams of isopropyl benzene component. A. 0.48 g B. 0.85 g C. 0.56 g D. 0.50 g E. 0.87 g Cl + + AlCl 3 benzene 1-chloropropane n-propylbenzene isopropylbenzene MW 78.2 g/mol MW 78.5 g/mol MW 120.2 g/mol MW 120.2 g/mol

4. As outlined in question 3, the areas of the two peaks on the chromatogram were - n-propyl benzene [area = 64 mm 2 , Wf -1.09] and isopropyl benzene [area = 115 mm 2 , Wf -1.04]. Calculate the reaction % yield of n-propyl benzene component. A. 21.8% B. 37.0% C. 58.8% D. 41.2% E. 35.8% 5. High-performance liquid chromatography (HPLC) is a type of: A. Molecular exclusion chromatography B. Partition chromatography C. Paper chromatography D. Adsorption chromatography Match the following HPLC columns with their corresponding characteristic. A. Reverse-phase chromatography column B. Normal phase chromatography column C. Ion exchange chromatography column D. Size exclusion chromatography column 6. A column packed with an adsorbent is coated with alkyl chains which makes it hydrophobic and has a strong affinity for non-polar compounds. A 7. The stationary phase is made up of cross-linked polymer with charged structural units that bind oppositely charged ionic components. C Use the periodic table below to answer question 8. 8. Which single bond would be expected to vibrate at the highest frequency? A. C-P B. C-S C. C-N D. C-O E. C-Si

9. In IR spectroscopy, absorption of radiation leads to which of the following? A. Changes in spin properties in the atoms B. Change in the compounds molecular weight C. Changes in bond dipole moments due to molecular vibrations D. Electronic transitions from ground state to excited state E. Rotations about single bonds leading to conformers 10. After an IR analysis of a product obtained from a synthesis, a student observed four major bands in the functional group region. Band W has a 47% transmittance, band X has a 53% transmittance, band Y has a 22% transmittance and band Z has a 78% transmittance. Which of the four bands has the greatest absorbance? A. band W B. band X C. band Y D. band Z E. Cannot be determined from the information provided 11. An IR spectrum of an organic compound showed a strong absorption band at 1680 cm -1 . Determine the wavelength in microns (μm) associated with this absorption. [1 μm = 0.0001 cm] A. 6.13 B. 8.22 C. 5.95 D. 4.75 E. 5.38 Use the IR spectrum below to answer questions 12-14. X Y Z

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A. O-H stretching vibrations - alcohol B. C=O stretching vibrations C. C-O stretching vibrations D. O-H stretching vibrations - carboxylic acid E. C-H stretching vibrations 12. Which of the above listed vibrations is responsible for band X? D 13. Which of the above listed vibrations is responsible for band Y? B 14. Which of the above listed vibrations is responsible for band Z? C 15. Analyze the IR spectrum below and determine the compound that most likely produces it A. Cyclohexanol B. Cinnamaldehyde C. Maleic anhydride D. Butyric acid E. Methyl ethyl ketone %T Wave number [cm -1 ] 1813 cm -1 1751 cm -1 1058 cm -1 3013 cm -1 3584 cm -1

A chem 335 student was tasked with synthesizing a Diels-Alder adduct of maleic anhydride and a diene in eucalyptus oil. [Question 16-18] 16. The gas chromatogram of the oil sample is shown below. Use it to determine the % composition of diene in the oil. [the diene corresponds to the largest peak] A. 59.8 % B. 60.1 % C. 63.2 % D. 60.8 % E. 58.9 % The diene in the sample is determined to be alpha terpinene [MW 136g/mol]. The amount of maleic anhydride [MW 98g/mol] used was intended to completely react with the diene in the oil sample to exactness. Q. W. X. Y. Z. Peak height Width at ½-height Q 2.2 cm 0.51 cm W 0. 5 cm 0.3 cm X 1.2 cm 0.3 cm Y 4.3 cm 1.3 cm Z 1.8 cm 1.1 cm O O O + Heat diethyl ether alpha terpinene maleic anhydride adduct

17. The student started with 3.6 g oil sample. After synthesis and purification, the final weight of product (adduct – MW 234g/mol) was determined to be 3.2 grams. Calculate the student’s overall reaction yield. A. 53.5 % B. 85.4 % C. 76.8 % D. 60.2 % E. 88.7 % 18. From the options below, determine the correct structure of the Diels-alder adduct formed from maleic anhydride and alpha-terpinene. :End O O O O O O O O O O O O O O O A B C D E

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