Sample NMR Starting Magnetic Field<\/p>\n Note the somewhat ordered field that already exists in the Z-direction. \u00a0This is what the initial field looks like most of the time: \u00a0the inhomogeneities are a complex function in three dimensions. \u00a0In order to make the magnetic field homogenous, it is modified using the shim system. The shim system is a series of uncooled, current carrying coils that generate fields in all three directions. \u00a0Each coil attempts to create a field with a function that precisely cancels the imperfections. \u00a0Numerous simple 3-D functions like All but the most experienced and exacting users of NMR use functions other than Optimal NMR Magnetic Field<\/p>\n Once the magnetic field is homogenized, the analysis of a sample can begin. \u00a0Each nucleus in the atom to be tested has its own resonant frequency somewhere in the radio section of the electromagnetic spectrum. \u00a0NMR takes advantage of this frequency’s dependence on the strength on an external magnetic field to gather information about each single nucleus, all at one time. \u00a0When the sample is placed in the now-homogenized magnetic field, the electrons around each nucleus become a current, and generate their own magnetic field in the opposite direction. \u00a0This effect is shown below, where the field of the NMR is blue, and the field created by the sample is red.<\/p>\n The smaller, red magnetic field decreases the influence of the NMR’s magnetic field on each nucleus and causes a very small shift in their resonant frequencies. \u00a0These shifts, which are dependent on the electron density around each nucleus, are calculated using the equation:<\/p>\n (1) <\/span> <\/span> The peaks that appear on NMR spectra are created when radio waves that match the now-altered resonant frequencies are absorbed and reradiated by the nuclei. \u00a0The four NMR spectra collected for 3,3-dimethyl-2-butanol are shown below as a sample of the gathered data.<\/p>\n Each peak in a Each peak in a The two spectra below are meant to be read together.<\/p>\n![\"\"](\"http:\/\/pages.vassar.edu\/magnes\/files\/2012\/04\/Initial-NMR-Magnetic-Field3.png\")
<\/a><\/p>\n are available to add to the magnetic field created by shimming. \u00a0Each set of coils creates a magnetic field gradient in its direction. \u00a0Below is a model of a correction field that uses the function :<\/p>\n<\/a><\/p>\n Correction Field<\/p>\n and in the correction field because the original field is usually close to homogenous. \u00a0The optimal field for doing NMR spectroscopy is shown below-it is perfectly homogenous and only in the Z-direction.<\/p>\n<\/a><\/p>\n<\/a>Magnetic field generated by a sample<\/p>\n<\/p>\n<\/a>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 3,3-dimethyl-2-butanol<\/p>\n<\/a>H-NMR Spectrum of 3,3-dimethyl-2-butanol<\/p>\nH-NMR spectrum\u00a0represents a certain number of hydrogen nuclei and describes their neighborhood in the molecule.<\/p>\n<\/a> C-NMR spectrum of 3,3-dimethyl-2-butanol<\/p>\n C-NMR spectrum\u00a0represents a specific “type” of carbon in the molecule. \u00a0One peak can represent more than one carbon nucleus if they have the same electron densities.<\/p>\n