{"id":1703,"date":"2012-04-22T16:18:15","date_gmt":"2012-04-22T20:18:15","guid":{"rendered":"http:\/\/blogs.vassar.edu\/magnes\/?p=1703"},"modified":"2013-07-11T10:29:36","modified_gmt":"2013-07-11T14:29:36","slug":"interpreting-a-h-nmr-spectrum","status":"publish","type":"post","link":"https:\/\/pages.vassar.edu\/magnes\/2012\/04\/22\/interpreting-a-h-nmr-spectrum\/","title":{"rendered":"Interpreting a H-NMR Spectrum"},"content":{"rendered":"

The NMR Spectrometer at Vassar college is graded at 300 MHz. \u00a0This means the Larmor frequency of a single, unaltered hydrogen nucleus and its electron with \"\sigma=0\", is 300 MHz. \u00a0The magnetogyric ratio \"\gamma\" of a hydrogen nucleus is 267.513\"*10^{6}\frac{rad}{T•s}\" . \u00a0A quick calculation using:<\/p>\n

(1) <\/span>   <\/span>\"\begin{equation*}<\/p>\n

shows the magnetic field strength of the NMR is roughly 7.046 T.<\/p>\n

Using this information and the \"^{1}\"H-NMR spectrum, we can calculate shielding factors for each type of hydrogen nucleus in 3,3-dimethyl-2-butanol, and determine what each spectrum peak actually means.<\/p>\n

\"\"<\/a><\/p>\n

\"\"<\/a><\/p>\n

Let’s start with the peak farthest to the right on the spectrum. \u00a0It is a single peak, called a singlet, that represents nine hydrogens, and is centered at approximately 0.9 ppm on the x-axis. \u00a0The ppm scale measures how much the Larmor frequency of hydrogen is changed by the effective magnetic field. \u00a0The Larmor frequency of the hydrogens represented by the first peak was increased by 0.9 ppm of the initial 300 MHz frequency. \u00a0A calculation of these hydrogens’ shielding factor follows using equation (1):<\/p>\n

\"300 MHz+(\frac{0.9 ppm}{10^{6}}*300 MHz)=\frac{267.513*10^{6}\frac{rad}{T•s}*7.046T*(1-\sigma)}{2\pi}\"<\/p>\n

\"300000270 Hz=299990611 Hz(1-\sigma)\"<\/p>\n

\"\sigma=-3.2198*10^{-5}\"<\/p>\n

Shielding factors tend to be small for most hydrogen nuclei. \u00a0A table of chemical shift and shielding factor values for each hydrogen nucleus in 3,3-dimethyl-2-butanol is below.<\/p>\n

\"\"<\/a><\/p>\n

A more negative shielding factor corresponds with a lower electron density around the hydrogen nucleus and with a larger effective magnetic field influencing the nucleus. \u00a0The presence of very electronegative atoms, like oxygen, near the hydrogen causes increased chemical shifts like the 3.5 ppm shift in the table.<\/p>\n

One peak in the spectrum above is split into two peaks centered around the chemical shift \u00a01.1 ppm. \u00a0This splitting occurs because there is another magnetically active hydrogen nucleus nearby in the molecule. \u00a0The rule for split peaks is: the number of nearby hydrogens is given by \"n-1\", where \"n\" is the number of peaks. \u00a0The definition of “nearby” is usually 1 carbon atom over in the molecule from the one the original hydrogen is attached to.<\/p>\n

The figure below shows the structure of 3,3-dimethyl-2-butanol with the hydrogens labeled with their corresponding chemical shifts. \u00a0This will be the first step in reconstructing the molecule from the NMR data.<\/p>\n

\"\"<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

The NMR Spectrometer at Vassar college is graded at 300 MHz. \u00a0This means the Larmor frequency of a single, unaltered hydrogen nucleus and its electron with , is 300 MHz. \u00a0The magnetogyric ratio of a hydrogen nucleus is 267.513 . \u00a0A quick calculation using: (1)   shows the magnetic field strength of the NMR is […]<\/p>\n","protected":false},"author":912,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4101,64,29905],"tags":[],"class_list":["post-1703","post","type-post","status-publish","format-standard","hentry","category-advanced-em","category-michael","category-spring-2012"],"_links":{"self":[{"href":"https:\/\/pages.vassar.edu\/magnes\/wp-json\/wp\/v2\/posts\/1703","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pages.vassar.edu\/magnes\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/pages.vassar.edu\/magnes\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/pages.vassar.edu\/magnes\/wp-json\/wp\/v2\/users\/912"}],"replies":[{"embeddable":true,"href":"https:\/\/pages.vassar.edu\/magnes\/wp-json\/wp\/v2\/comments?post=1703"}],"version-history":[{"count":100,"href":"https:\/\/pages.vassar.edu\/magnes\/wp-json\/wp\/v2\/posts\/1703\/revisions"}],"predecessor-version":[{"id":1852,"href":"https:\/\/pages.vassar.edu\/magnes\/wp-json\/wp\/v2\/posts\/1703\/revisions\/1852"}],"wp:attachment":[{"href":"https:\/\/pages.vassar.edu\/magnes\/wp-json\/wp\/v2\/media?parent=1703"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/pages.vassar.edu\/magnes\/wp-json\/wp\/v2\/categories?post=1703"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/pages.vassar.edu\/magnes\/wp-json\/wp\/v2\/tags?post=1703"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}