When the ^1 H NMR spectrum of acetone, CH3 COCH3, is recorded on an instrument operating at 200

step 1 We're going to be looking at some basics of NMR. So looking at the NMR spectrum of acetone, whic

When the ^1 H NMR spectrum of acetone, CH3 COCH3, is...

When the ${ }^{1} \mathrm{H}$ NMR spectrum of acetone, $\mathrm{CH}_{3} \mathrm{COCH}_{3},$ is recorded on an instrument operating at $200 \mathrm{MHz}$, a single sharp resonance at $2.1 \delta$ is seen. (a) How many hertz downfield from TMS does the acetone resonance correspond to? (b) If the 1 H NMR spectrum of acetone were recorded at $500 \mathrm{MHz}$, what would the position of the absorption be in $\delta$ units? (c) How many hertz downfield from TMS does this 500 MHz resonance correspond to?

When the ${ }^{1} \mathrm{H}$ NMR spectrum of acetone, $\mathrm{CH}_{3} \mathrm{COCH}_{3},$ is recorded on an instrument operating at $200 \mathrm{MHz}$, a single sharp resonance at $2.1 \delta$ is seen.
(a) How many hertz downfield from TMS does the acetone resonance correspond to?
(b) If the 1 H NMR spectrum of acetone were recorded at $500 \mathrm{MHz}$, what would the position of the absorption be in $\delta$ units?
(c) How many hertz downfield from TMS does this 500 MHz resonance correspond to?

Labs

Want to see this concept in action?

NEW

Explore this concept interactively to see how it behaves as you change inputs.

View Labs

Key Concepts

Chemical Shift

Chemical shift in nuclear magnetic resonance (NMR) spectroscopy is a dimensionless measure expressed in parts per million (ppm). It represents the resonance frequency of a nucleus relative to a standard reference compound, often tetramethylsilane (TMS). This measure is independent of the magnetic field strength or the instrument’s operating frequency, allowing for comparisons across different spectrometers.

Conversion from ppm to Hertz

In NMR, although chemical shifts are reported in ppm, the actual frequency difference in hertz can be calculated by multiplying the chemical shift value (in ppm) by the operating frequency of the instrument (in MHz). For example, a shift of 2.1 ppm on a 200 MHz instrument corresponds to a frequency difference of 2.1 × 200 Hz.

Instrument Operating Frequency and its Effect

The operating frequency of an NMR spectrometer affects the absolute frequency difference in hertz between resonances, even though the chemical shift in ppm remains constant. Thus, on a higher field instrument (e.g., 500 MHz), the same ppm value corresponds to a greater hertz value, which illustrates the linear relationship between operating frequency and frequency differences in Hz.

Transcript

Please give Ace some feedback