Proton nuclear magnetic resonance

Proton nuclear magnetic resonance (proton NMR, hydrogen-1 NMR, or 1H NMR) is the application of <a href="/facts/Nuclear_magnetic_resonance/pGYAn9Bz">nuclear magnetic resonance</a> in <a href="/facts/NMR_spectroscopy/SFKgdthI">NMR spectroscopy</a> with respect to <a href="/facts/Hydrogen-1/c3CAg2Pc">hydrogen-1</a> <a href="/facts/Atomic_nucleus/orpIm5Xl">nuclei</a> within the <a href="/facts/Molecules/N9ljSfFq">molecules</a> of a substance, in order to determine the structure of its molecules. In samples where natural <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a> (H) is used, practically all the hydrogen consists of the <a href="/facts/Isotope/KD9B1y6o">isotope</a> 1H (hydrogen-1; i.e. having a <a href="/facts/Proton/clCjepXP">proton</a> for a nucleus).
Simple NMR spectra are recorded in <a href="/facts/Solution_(chemistry)/MGchhMQV">solution</a>, and <a href="/facts/Solvent/LoMPMz8S">solvent</a> protons must not be allowed to interfere. <a href="/facts/Deuterium/Bv4wfCkw">Deuterated</a> (deuterium = 2H, often symbolized as D) solvents especially for use in NMR are preferred, e.g. <a href="/facts/Heavy_water/3dbSrTw5">deuterated water</a>, D2O, deuterated <a href="/facts/Acetone/cVyJxKqw">acetone</a>, (CD3)2CO, deuterated <a href="/facts/Methanol/EIfpoNCg">methanol</a>, CD3OD, <a href="/facts/Deuterated_dimethyl_sulfoxide/gR1EWBRo">deuterated dimethyl sulfoxide</a>, (CD3)2SO, and <a href="/facts/Deuterated_chloroform/Md4bJN0w">deuterated chloroform</a>, CDCl3. However, a solvent without hydrogen, such as <a href="/facts/Carbon_tetrachloride/S2ekjT0E">carbon tetrachloride</a>, CCl4 or <a href="/facts/Carbon_disulfide/b04Tadmy">carbon disulfide</a>, CS2, may also be used.
Historically, deuterated solvents were supplied with a small amount (typically 0.1%) of <a href="/facts/Tetramethylsilane/05nHMHJU">tetramethylsilane</a> (TMS) as an <a href="/facts/Internal_standard/YdqEc1vq">internal standard</a> for referencing the <a href="/facts/Chemical_shift/VoCY7s7R">chemical shifts</a> of each analyte proton. TMS is a <a href="/facts/Tetrahedral_molecular_geometry/583AL1sP">tetrahedral</a> molecule, with all protons being chemically equivalent, giving one single signal, used to define a chemical shift = 0 ppm.
 
It is <a href="/facts/Volatility_(chemistry)/90r3ep6w">volatile</a>, making sample recovery easy as well. Modern spectrometers are able to reference spectra based on the residual proton in the solvent (e.g. the CHCl3, 0.01% in 99.99% CDCl3). Deuterated solvents are now commonly supplied without TMS.
Deuterated solvents permit the use of deuterium frequency-field lock (also known as deuterium lock or field lock) to offset the effect of the natural drift of the NMR's magnetic field 
 
 
 
 
 B
 
 0
 
 
 
 
 {\displaystyle B_{0}}
 
. In order to provide deuterium lock, the NMR constantly monitors the deuterium signal resonance frequency from the solvent and makes changes to the 
 
 
 
 
 B
 
 0
 
 
 
 
 {\displaystyle B_{0}}
 
 to keep the resonance frequency constant. Additionally, the deuterium signal may be used to accurately define 0 ppm as the resonant frequency of the lock solvent and the difference between the lock solvent and 0 ppm (TMS) are well known.
Proton NMR spectra of most organic compounds are characterized by <a href="/facts/Chemical_shift/VoCY7s7R">chemical shifts</a> in the range +14 to -4 ppm and by <a href="/facts/Spin%E2%80%93spin_coupling/xsfw1hBG">spin–spin coupling</a> between protons. The <a href="/facts/Integral/V7lyV997">integration curve</a> for each proton reflects the abundance of the individual protons.
Simple molecules have simple spectra. The spectrum of <a href="/facts/Ethyl_chloride/6DjUIuH7">ethyl chloride</a> consists of a triplet at 1.5 ppm and a quartet at 3.5 ppm in a 3:2 ratio. The spectrum of <a href="/facts/Benzene/Fguue7nr">benzene</a> consists of a single peak at 7.2 ppm due to the <a href="/facts/Diamagnetic_ring_current/CLljRq2c">diamagnetic ring current</a>.
Together with <a href="/facts/Carbon-13_NMR/0RlV1ajq">carbon-13 NMR</a>, proton NMR is a powerful tool for molecular structure characterization.

Proton nuclear magnetic resonance open-in-new

Proton nuclear magnetic resonance