CHEM 2211 1st Edition Lecture 13 Outline of Last LectureI. Brief intro to HNMRII. Shielding effects of NMRIII. Number of Signals in HNMRIV. Chemical ShifOutline of Current LectureI. Integrating NMR signalsII. Splitting signal is described by the N+1 ruleIII. What causes splitting?IV. Coupling constant identifies coupled protonsV. Diastereotopic hydrogens are not equivalentVI. Time dependency of NMRsCurrent LectureI. Integrating the NMR signalsA. The signals produced by the hydrogens of a compound vary in height because the area under each signal is proportional to the number of protons producing the signalB. On older graphs, the integral is shown to be an integral trace. The height of each step is the approximate number of hydrogens.C. Modern graphs impose the integral number onto the graph above the corresponding peakII. Splitting of signal is described by the N+1 ruleA. An explanation for the multiple peaks at point son the graphB. Caused by the protons bonded to neighboring carbonsC. N+1 rule is as follows: number of hydrogens on non-equivalent neighboring carbons + 1 = number of peaks on graphIII. What causes splitting?A. The peaks represent the number of ways that the protons can align with or against the magnetic fieldB. Refer to figures 15.15 and 15.16 in the book for the most accurate representationof this conceptIV. Coupling constant identify coupled protonsA. J denotes the coupling constant and is defined as the distance between the peaksof a split NMR signalB. Equivalent hydrogens have the same J valueC. J values are constant despite a change in magnetic field and frequencyV. Diastereotopic hydrogens are not equivalentA. Carbon bonded to two hydrogens and two other nonequivalent groups have enantiotropic hydrogens because changing one of the hydrogens to another group will result in a pair of enantiomers. This is called a prochiral center.B. A carbon attached to two hydrogens and is a part of an asymmetric center has diastereotopic hydrogens, because replacing one of the hydrogens creates a diastereomers.VI. Time dependence of NMR spectroscopyA. Each graph represents an average of the molecule’s conformers because the molecules are constantly
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