Rules of the Day 1-22-07

1. We care about the nuclei 1H and 13C since these are commonly found in organic molecules and they have spin quantum numbers of 1/2.

2. Nuclei with spin quantum number 1/2 are quantized in one of two orientations, "+1/2" (lower energy) or "-1/2"(higher energy) in the presence of an external magnetic field, that is, with and against the external field, respectively.

2. The difference in energy between the +1/2 and -1/2 nuclear spin states is proportional to the strength of the magnetic field felt by the nucleus.

3. NMR spectra record the energy (plotted as frequency) necessary for the nuclei to be excited from the lower energy spin state to the higher energy spin state in the presence of a strong external magnetic field. Different atoms in a molecule take different amounts of energy to accomplish this, and the different energies can be correlated to structure of the molecule.

4. Electron density is induced to circulate in a strong external magnetic field, which in turn produces a magnetic field that opposes the external magnetic field. This shields nuclei from the external magnetic field. The greater the electron density around a nucleus, the more shielded it is, and the lower the energy (frequency) of electromagnetic radiation required to flip its nuclear spin.

5. Electronegative atoms, pi bonds and hybridization state of carbon atoms attached to an H atom influence shielding in predictable ways by removing differing amounts of electron density around adjacent nuclei.

Homework: Continue working on homework review problem set, due Wed. , 1-24-07, BEFORE CLASS. Click here to download the pdf.

Continue making a Roadmap for 310M reactions. Reread: The first half of Chapter 13 in the book, THEN read the "NMR theory web handout" Work Problems: Try 13.15-13.18 in the book. Struggling through these will make the lectures at the end of the week much easier to understand. I know I have not covered any of this material, but if you do this homework BEFORE Friday's class, the lecture will make a LOT more sense to you!!!!!! TRY IT!!!!!!