Important Concepts 10 1.NMR – Most important spectroscopic tool for elucidating organic structures. 2.Spectroscopy – Based on lower energy forms of molecules being converted into higher energy forms by the absorption of electromagnetic radiation. 3.NMR – Based on alignment of the nuclei of certain nuclei (i.e.. 1 H and 13 C) with (  ) and against (  ) a strong magnetic field.  to  transition affected by radio-frequency radiation leading to resonance and characteristic absorption spectra. High magnetic fields lead to higher resonant frequencies. 4.High Resolution NMR – Allows differentiation of 1 H and 13 C nuclei in different environments. Spectral positions are measured as the chemical shift, δ, in ppm from an internal standard (TMS).

Important Concepts 10 5.Chemical Shifts – Highly dependent on presence (shielding) or absence (deshielding) of electron density. Electron donor substituents shield. Electron withdrawing substituents deshield. Hydrogen bonding or proton exchange result in broad peaks. 6.Chemical Equivalency – Equivalent hydrogens or carbons have the same chemical shift. 7.Integration of peak area indicates number of contributing hydrogens. 8.Spin-Spin Splitting – Pattern determined by number of hydrogen neighbors (N+1 Rule). Equivalent hydrogens show no mutual splitting.

Important Concepts 10 9.Non-First-Order Spectra – Complicated patterns created when chemical-shift difference between coupled hydrogens is comparable to their coupling constant. 10.Non-Equivalent Neighboring Hydrogens – (N + 1) rule is applied sequentially. 11.Carbon NMR – Utilizes low abundance 13 C nuclei. C-C coupling is not observed. C-H coupling can be removed by proton decoupling. 12.DEPT 13 C NMR – Allows peak assignment to CH 3, CH 2, CH, and quaternary carbons respectively.