Rules of the Day 1-24-07

1. 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.

2. The location of a given signal with respect to a standard, TMS, is called chemical shift (d) and this has the units ppm (parts per million). The more shielded the nucleus, the smaller the chemical shift. Different functional groups have characteristic chemical shifts.

3. Equivalent hydrogen atoms in a molecule give the same NMR signal. Equivalent hydrogen atoms in a molecule have an identical relationship to all the other atoms in the molecule, and are found on the same sp3 atom (bond rotation makes them equivalent) or entire groups are equivalent due to symmetry in the molecule. Determining how many equivalent hydrogens are in a molecule can be very tricky (Skull and Crossbones!).

4. The size (integration) of the signal in an 1H NMR spectrum is proportional to the number of equivalent hydrogens in each signal.

5. Adjacent nuclei have magnetic fields associated with their spins and the magnetic field produced by a +1/2 nucleur spin is different than the magnetic field produced by a -1/2 nuclear spin.

Homework: Start working on the second homework problem set, due Fri. , 2-2-07, BEFORE CLASS. Click here to download the pdf.

Finish making a Roadmap for 310M reactions. Reread: Section 13.8 , THEN read the second "NMR theory web handout"