NMR: Information Obtained from a Spectrum An NMR Spectrum will generally provide three types of information: Chemical Shift – indicates the electronic environment of the nucleus (shielded or deshielded) Integration – gives the relative number of nuclei producing a given signal. The integral (area under the curve) is drawn on the spectrum by the instrument. Spin-Spin Coupling – describes the connectivity

NMR: Integration Indicates Relative Number of Nuclei Integral has relative height 9 Relative height 2 The height of the integration line (“integral”) gives you the relative number of nuclei producing each signal.

NMR: Information Obtained from a Spectrum An NMR Spectrum will generally provide three types of information: Chemical Shift – indicates the electronic environment of the nucleus (shielded or deshielded) Integration – gives the relative number of nuclei producing a given signal Spin-Spin Coupling: - describes the carbon connectivity - follows the “n+1”rule”

NMR: Splitting into a Doublet Note that the red signal at 1.6 ppm for the methyl group is split into two peaks. Remember that this is one signal, composed of two separate peaks.

NMR: Signal Splitting, n+1 Rule A signal is often split into multiple peaks due to interactions with protons on carbons next door. Called spin-spin splitting The splitting is into one more peak than the number of H’s on adjacent carbons (“n+1 rule”) Splitting of a signal can give doublets (two peaks), triplets (three peaks), quartets (4 peaks), ect. The relative intensities given by Pascal’s Triangle: doublet 1 : 1 triplet 1 : 2 : 1 quartet 1 : 3 : 3 : 1 pentet: 1 : 4 : 6 : 4 : 1

NMR: Signal Splitting, n+1 Rule n+1 Rule: A signal in the proton NMR spectrum will be split into n+1 peaks, where n is the number of protons on adjacent carbons. Example: CH3-CH2-Br For the Methyl Group – There are two protons ‘next door’ (n=2), so the methyl signal will be split into three peaks (2+1), which is called a triplet. Chemical shift will be about 1.5 (alkane region), integration = 3. For the CH2 Group – Three protons next door will give a signal with 3+1 = 4 peaks, called a quartet. Chemical shift = 3.3 (heteroatom region), integration = 2.

NMR: Signal Splitting, n+1 Rule Peak Heights - Pascal’s Triangle doublet 1 : 1 triplet 1 : 2 : 1 quartet 1 : 3 : 3 : 1 pentet 1 : 4 : 6 : 4 : 1