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Ch. 15 - Structural Identification 2: Nuclear Magnetic Resonance Spectroscopy
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
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Tutti i libri di testoMullins 1st EditionCh. 15 - Structural Identification 2: Nuclear Magnetic Resonance SpectroscopyProblema 21
Capitolo 14, Problema 21

(a) Calculate the resonance frequency of an aldehydic proton ( δ 9.3 ppm) if it is detected on a 60-MHz NMR spectrometer.
(b) What if it were detected on a 300-MHz instrument?

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1
Understand that the resonance frequency of a proton in NMR is determined by the chemical shift (δ) and the operating frequency of the NMR spectrometer.
The chemical shift (δ) is given in parts per million (ppm) and represents the difference in resonance frequency of the proton relative to a reference compound, usually TMS (tetramethylsilane).
To calculate the resonance frequency, use the formula: \( \text{Resonance Frequency} = \delta \times \text{Operating Frequency} \).
For part (a), substitute the given values into the formula: \( 9.3 \text{ ppm} \times 60 \text{ MHz} \).
For part (b), substitute the given values into the formula: \( 9.3 \text{ ppm} \times 300 \text{ MHz} \).

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NMR Spectroscopy

Nuclear Magnetic Resonance (NMR) Spectroscopy is a technique used to observe the local magnetic fields around atomic nuclei. It provides detailed information about the structure, dynamics, and environment of molecules. The resonance frequency of a nucleus in an NMR spectrometer depends on the strength of the external magnetic field and the chemical environment of the nucleus.
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General NMR Features

Chemical Shift

Chemical shift is a key concept in NMR spectroscopy, representing the resonance frequency of a nucleus relative to a standard reference. It is measured in parts per million (ppm) and provides insight into the electronic environment surrounding the nucleus. The chemical shift is influenced by factors such as electronegativity and hybridization of nearby atoms.
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1H NMR Chemical Shifts

Resonance Frequency Calculation

Resonance frequency in NMR is calculated using the formula: frequency = chemical shift × spectrometer frequency. For an aldehydic proton with a chemical shift of δ 9.3 ppm, the resonance frequency can be determined by multiplying the chemical shift by the spectrometer's operating frequency, such as 60 MHz or 300 MHz, to find the specific frequency at which the proton resonates.
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Drawing Resonance Structures
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