Rules of the Day 1-23-08

1. Equivalent hydrogen atoms in a molecule have an identical relationship to all the other atoms (they are in the same chemical environment) in the molecule. Determining how many equivalent hydrogens are in a molecule can be very tricky (Skull and Crossbones!)

2. Here are functional definitions of equivalent hydrogens. A) Equivalent hydrogens are found on the same sp3 atom that can rotate freely in a moleclue. B) Entire groups of hydrogen are equivalent due to overall symmetry in a molecule, including cases in which bond rotation introduces the symmetry (i.e. the six equivalent hydrogens on the two methyls of an isopropyl group).

3. Equivalent hydrogen atoms in a molecule give the same NMR signal.

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. The spins of equivalent adjacent nuclei can be either +1/2 or -1/2, and at room temperature they are found in about a 50:50 mixture at any given nucleus (very slight excess of lower energy +1/2). These can add to give n+1 different spin combinations in the proportions predicted by Pascal's triangle. Each different spin combination produces a different magetic field, which leads to n+1 splittings in the peaks of the NMR spectra of the adjacent (no more than three bonds away) nuclei.

Homework: Start working on the second homework problem set, due Fri. , 2-1-08, BEFORE CLASS. Click here to download the pdf.

Finish making a Roadmap for 310M reactions. Reread: Section 13.8 , THEN read the second "NMR handout" called How to Interpret an NMR Spectrum