ORGANIC CHEMISTRY

Assignment

1
H NMR (3)
Multiple Choic Questions (MCQs)
1. The signal for OH in 1H NMR of benzyl alcohol in a 60 MHz NMR Instrument was found to be
at 144 Hz higher frequency than TMS. Calculate the chemical shift of –OH proton in ppm.
(a) 2.4 (b) 2.5 (c) 2.3 (d) 3
2. The signal for –CH2 protons in the 1H NMR of benzyl alcohol in a 300 MHz NMR Instrument
was found to be at 4.6 ppm. Calculate the difference in frequency, expressed in Hz, between this
and TMS signal.
(a) 300 Hz (b) 3000 Hz (c) 1380 Hz (d) 1300 Hz
3. Consider the same data given in previous question. What would have been the chemical shift of
each signal if a 250 MHz instrument has been used?
(a) No effect on chemical shift (b) Chemical shift will increase

4.
CHEM ACADEMY
(c) Chemical shift will decrease
1
(d) None of these
The 250 MHz H NMR spectrum of methyllithium shows a signal at 525 Hz upfield of TMS.
What is the chemical shift?
(a) 2.10 ppm (b) –2.10 ppm (c) Both (a) and (b) (d) 3.0 ppm
5. What field strength is needed to generate a 250 MHz 1H spectrum?
(a) 1.41 T (b) 1.26 T (c) 5.87 T (d) None of these
6. What is the position of the methyl signal in (Hz) of toluene down field to TMS? (Given operating
frequency 250 MHz)
(a) 250 Hz (b) 586 Hz (c) –600 Hz (d) 700 Hz
7. A proton has resonance 90 Hz downfield from TMS when field strength is 1.41 Tesla (14, 100
Gauss) and the oscillator frequency is 60 MHz.
What will be its shift in Hertz if the field strength is increased to 2.82 Tesla and the oscillator
frequency to 120 MHz.
(a) 120 Hz (b) 90 Hz (c) 180 Hz (d) 200 Hz
8. A proton has resonance 90 Hz downfield from TMS when the field strength is 1.40 Tesla (14, 100
Gauss) and the oscillator frequency is 60 MHz.
What will be its chemical shift in parts per million()?
(a) 1.2 (b) 1.3 (c) 1.4 (d) 1.5
9. For a certain magnetic field strength, a free proton spin transistion occurs at 700 MHz. Keeping
the magnetic field strength constant the 14N Nucleus will resonate at (g(p)  5.6 and (14N = 0.4).
(a) 700 MHz (b) 400 MHz (c) 200 MHz (d) 50 MHz
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10. The g-factors of 1H and 13C are 5.6 and 1.4 respectively. For the same value of the magnetic field
strength, if the 1H resonates at 600 MHz, the 13C would resonate at
(a) 2400 MHz (b) 600 MHz (c) 150 Hz (d) 38 MHz
11. Which of the following nuclei have lowest sensitivity in NMR experiment?
(a) 1H (b) 11B (c) 13C (d) 19F
12. A peak in a proton NMR spectrum is located at 1.5 ppm from the refrence TMS on a 400 MHz
NMR spectrometer. If the refrence is set to 0 ppm, what is the separation of the peak from
refrence as calculated in Hz scale?
(a) 800 Hz (b) 600 Hz (c) 500 Hz (d) 400 Hz
13. Calculate the chemical shifts of the two (in  units) toluene signals obtained at 180 Hz and 578 Hz
using the 80 MHz data?
(a) 7.65, 2.7 (b) 2.35, 7.23 (c) Both (a) and (b) (d) None of these
14. Arrange the following atoms from most electronegative to least H, Li, C, Si.
(a) C > H > Si > Li (b) C > Si > H > Li (c) H > C > Si > Li (d) Li > Si > C > H
18. Arrange the following underlined hydrogens from most deshielded to least
H3C – H, H3C – Li, H3C – C, H3C – Si
(a) H3C – H > H3C – Li > H3C – C > H3C – Si

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(b) H3C – C > H3C – H > H3C – Si > H3C – Li
(c) H3C – Li > H3C – H > H3C – C > H3C – Si
(d) H3C – Si > H3C – H > H3C – C > H3C – Li
15. Paramagnetic shielding cause a nucleus to process at
(a) Higher frequency (b) Lower frequency (c) Same frequency (d) None of these
Multiple Select Questions (MSQs)
16. Toluene at 80 MHz, exhibit two signals one at 188 Hz downfield and another at 573 Hz. Calculate
the chemical shift of the signals in ppm?
(a) 2.35 ppm (b) 7.23 ppm (c) 2.10 ppm (d) 7.65 ppm
Numerical Answer Type (NAT)
17. At on operating frequency of 350 MHz, the shift (in Hz) of resonance from TMS(tetramethylsilane)
of a proton with chemical shift of 2 ppm is _________.
18. Calculate the chemical shift in parts per million() for a proton that has resonance 128 Hz downfield
from TMS on a spectrometer that operates at 60 MHz _________. (in ppm)

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 ANSWER KEY
Multiple Choic Questions (MCQs)
1. a 2. c 3. a 4. b 5. c 6. b 7. c
8. d 9. d 10. c 11. c 12. b 13. a 14. a
18. b 15. a 16. a, b 17. 700 18. 2.1

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• Head Office: North Delhi: 72, Mall Road, G.T.B. Nagar, New Delhi - 110009
Ph.: 011-41415514, 09136597244, Web.: www.chemacademy.in 3
Branches: Jaipur | Pune | Kolkata