4. Which of the following is not true regarding 'H NMR spectroscopy? (d) a. "shielding" leads to peaks at lower values of & b. (s) a "downfield" peak appears at a higher value of & 8 for a particular proton depends on the magnetic field strength of the instrument used. d. с. on a 300 MHz instrument, a proton that adsorbs irradiation at a frequency 1200 Hz higher than the adsorption of TMS appears at 8 4 ppm.

• ${}^{\mathbf{1}}\mathit{H}\mathbf{-}\mathit{N}\mathit{M}\mathit{R}$:- It is proton nuclear magnetic resonance.
• Chemical shift($\mathit{\delta }$):- It maybe defined as the shift in the position of NMR absorption region sure to shielding and deshielding by the electrons.
• Shielding:- Shift of NMR signal towards right side of the NMR spectrum.
• Deshielding:- Shift of NMR signal towards left side of the NMR spectrum.
• TMS is tetramethylsilane which has $\delta =0$(approximately).

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