24. Devise a synthesis of B from A: 25. a. Which of the following statements is

Question

24. Devise a synthesis of B from A: 25. a. Which of the following statements is true about 'H NMR absorptions? A signai that occurs at 1800 Hz on a 300 MHz NMR spectrometer occurs at 3000 Hz on a 500 MHz NMR spectrometer i. 2. A signal that occurs at 3.3 ppm on a 60 MHz NMR absorbs at 198 Hz upfield from TMS 3. A signal that occurs at 600 Hz is downfield from a signal that occurs at 800 Hz 4. Statements (1) and (2) are both true. 5. Statements (1), (2), and (3) are all true. b. Which of the following statements is true about 'H NMR spectroscopy? i. Electronegative elements shield a nucleus so an absorption shifts downfield. 2. A triplet is due to a proton that has four adjacent nonequivalent protons 3. Circulating electrons create a magnetic field that reinforces the applied field in the 4. 5. vicinity of the protons in benzene. Statements (1) and (2) are both true. Statements (1), (2), and (3) are all true. 26. Into how many peaks will each of the circled protons be split in a proton NMR spectrum? c. d. 27.

Explanation / Answer

25.a)

1. True     Chemical sgift = frequency of signal / spectrometer frequency = 1800/300 =6 ppm

                                                                                                         = 3000/500 = 6 ppm

2. False   TMS protons are highly shielded and the chemical shift is considered to be 0. Generally all the protons are downfield to TMS signal.

3. False As frequencies increase, the signal shifts further downfield.

4. False

5. False

25.b)

1. False   Electronegativity element deshield a nucleus and signal shifts to downfield.

2. False A triplet is due to two non equivalent protons (n+1rule) on adjacent carbons.

3. True The given statement is true.

4. False

5. False

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