Aldol Post-Lab 8-28 Hyperlink

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CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 1 Aldol Reaction Post-Lab Questions T1: N MR Spectra For this Post-lab exercise, all the N MR spectra shown in the questions were acquired from one of the aldol products produced from this experiment: T1.1 Name the splitting pattern for the set of peaks shown in the outlined box below: a. Doublet b. Triplet c. Quartet d. A doublet of doublets e. Multiplet f. Impurity peaks to be ignored g. Four singlets T1.2 Identify the splitting pattern for the set of peaks shown in the outlined box below: a. One set of octet b. Two sets of doublets c. Two sets of doublet of doublets d. One set of doublet of doublets e. Multiplet f. Two quartets g. Impurity peaks to be ignored

CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 2 T1.3 The two diastereotopic hydrogens generate peaks as shown below. The values of the coupling constants “J” are indicated in the spacings denoted as a, b, c, and d, and are determined to be 6, 16, 6, 14 Hz respectively. Identify the type of J for each gap. See Hint. a. a= 3 J b= 2 J c= 2 J d= 3 J b. a= 3 J b= 2 J c= 3 J d= 2 J c. a= 2 J b= 3 J c= 2 J d= 3 J d. a= 2 J b= 2 J c= 2 J d= 3 J 2J 3J

CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 3 T1.4 (Part I) Calculate the J value using a 300Hz NMR spectrometer for the ppm values given below. a. 0.054 Hz b. 16.2 Hz c. 11.5 Hz d. 1.6- Hz e. 0.030 ppm

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CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 4 T1.4 (Part II) Calculate the J value using a 500Hz NMR spectrometer for the ppm values given below. a. 12 Hz b. 10 Hz c. 5 Hz d. 7.5 Hz e. 0.015 ppm T1.5 Comparing Part I and Part II in T1.4 , determine the relationship between the two protons. Which of the following statement(s) is/are correct ? a. Part I refers to 3 J (coupling between vicinal protons) b. Part I refers to 2 J (coupling between diastereotopic protons) c. Part II refers to 3 J (coupling between vicinal protons) d. Part II refers to 2 J (coupling between diastereotopic protons) e. B and C f. A and D g. A and C h. B and D

CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 5 T1.6 The proton H a in the structure below will most likely produce what type of signal in the proton NMR spectrum? a. One doublet b. One triplet c. One quartet d. A doublet of doublets e. None of these T1.7 The H b in below structure will most likely produce what type of signal in the proton NMR spectra? a. One doublet b. One triplet c. A doublet of doublets d. One quartet e. None of these M M M o

CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 6 T1.8 Calculate the J value using a 500Hz NMR spectrometer for the peaks indicated by the arrows below. a. 1.65 Hz b. 7.75 Hz c. 7.66 Hz d. 1.11 Hz e. None of these T1.9 Which two protons will likely produce the spin-spin-coupling at the highest range in Hz? a. H-H Vicinal, cis (6-15 Hz) b. H-H Vicinal, trans (11-18 Hz) c. H-H Geminal (0-5 Hz) d. H-H Geminal (9-18 Hz) e. H-H ortho (6-10 Hz)

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CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 7 T1.10 If a hydrogen atom produces a set of doublet of doublets on the NMR spectra, how many chemically non-equivalent proton(s) are most likely adjacent to this hydrogen atom? a. 1 b. 2 c. 3 d. 4 e. 0 T2 J values and Karplus relationship plot T2.1 The J values between H c and H b in the figure can be identified as: b . 3 J, and value of 3 J is usually greater than 2 J c. 1 J, and value of 1 J is much greater than 2 J d. 3 J, and value of 3 J is usually greater than 1 J e. There is no coupling between Hb and Hc

CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 8 T2.2 Which of the following tree diagrams most likely corresponds to Hc? See Hint. a. I b. II c. III d. IV e. None of these

CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 9 T2.3 Which of the following tree diagrams most likely corresponds to Ha? a. I b. II c. III d. IV e. None of these

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CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 10 T2.4 Which of the following tree diagrams most likely corresponds to Hc? a. I b. II c. III d. IV e. None of these

CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 11 T2.5 In the molecule below , both R and R’ are phenyl group s. By using the Karplus relationship plot, which pair(s) of dihedral angles could achieve the most stable confirmation that potentially corresponds to 3 J HH = 4.0 Hz and 3 J HH = 13.0 Hz ,. See Hint. a.  1 = 0 ° and  2 = 112 ° b.  1 = 60 ° and  2 = 155 ° c.  1 = 0 ° and  2 =160 ° d.  1 = 60 ° and  2 = 112 ° e.  1 = 180 ° and  2 = 111 ° f.  1 = 60 ° and  2 = 60 ° g. Both A and C are possible h. Both C and D are possible i. Both E and F are possible a 3 Jun 7 144 t 5682 3JH s 4,0 Ha 3 Jan 13.0 Hz 4 62 or 112 4 O or 160 I I either option either option bid or f b or c

CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 12 T2.6 The following Newman Projections represent the possible structures that can be formed for a compound with values 3 J HH = 4.0Hz and 3 J HH = 9.0 Hz. What structure represents the most stable conformation? a. Structure 1 b. Structure 2 c. Structure 3 d. Structure 4 e. Structure 5 f. None of the above structures are the most stable T2.7 Besides dihedral angles, what other factors are to be considered when determining the most stable conformation of a molecule? a. Steric effect b. Dipole-dipole interaction c. Hydrogen bonding d. All of the above e. None of these, dihedral angles are the only factors to consider when drawing the Newman Projection of the molecule.

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CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 13 T2.8 In this experiment, the aldol product wa s purified and eluted from the column… a. at the initial stage of elution b. toward the terminal stage of elution c. before benzaldehyde and thioester were eluted d. after benzaldehyde and thioester had been eluted e. by a solvent mixture of relatively low polarity f. by a solvent mixture of relatively high polarity g. A, C, E h. A, C, F i. B, D, F j. B, C, E Potential Post-Lab Free Response Questions: 1. Another way to carry out an aldol reaction is to use a pre-made, stable enol ether as the nucleophile. The enol ether is synthesized according to the following reaction: an enol ether (a) Write a reasonable mechanism for the enol ether formation. Note the reaction’s similarity to how the magnesium enolate intermediate formed in the aldol reaction you carried out in CHEM 420. (b) The enol ether is then allowed to react with an aldehyde in the presence of a Lewis acid, such as TiCl 4 , to form the aldol product. Write a reasonable mechanism for this reaction, which involves the Lewis acid, much like how the magnesium metal center functioned in the aldol reaction performed in CHEM 420.

CHEM 420 Aldol Rx. & Karplus Equation – Post-Lab Questions 14 2 2 2. A group of CHEM 420 students at CSU San Quintin, while serving time there, carried out the following aldol experiment. (a) Draw the expected structure of the aldol product for this experiment. (b) Draw all of the stereoisomers of the expected aldol product these inmates (I mean students) could expect to form in this experiment. Give clearly drawn structures with wedge and dash bonds to all indicate stereochemistry. (c) What are the stereochemical relationships among all of the structures you draw in part a? (d) Would you expect them to all form at the rate? Why or why not? Briefly explain by using your knowledge of kinetically controlled reactions from CHEM 220B.