Rules of the Day 320N

2. The 1,2 addition is usually the kinetic product, that is, it forms faster (better opportunity since the reaction is occuring at a more stabilized secondary carbocation), but the 1,4 addition product is the thermodynamic product because it is more stable (greater motive since the double bond is more substituted). At low temperature, in which the molecules cannot equilibrate, the kinetic product predominates (called kinetic control). At higher temperature, in which the products do equilibrate with each other, the thermodynamic product predominates (called thermodynamic control).

3. Think of electron density as waves, in which you can get extra stability when waves add constructively, and you lose stability when waves cancel each other (add destructively).

4. You generate as many new molecular orbitals as atomic orbitals used to create them. Half are bonding molecular orbitals (waves add constructively) and are filled with electron density, and half are antibonding molecular orbitals (waves add destructively) and are not filled with electron density.

5. Provided all the atoms are in the same plane, all adjacent 2p orbitals overlap, allowing the pi electron density to delocalize into all the adjacent 2p orbtials, their wave functions adding constructively to provide for extra stability. (See Golden Rule #7). This situation is officially referred to as conjugation, although in class I will call it a "pi-way". For a "pi-way" to exist, there can be no sp3 hybridized atoms between the overlapping 2p orbitals, and all the overlapping 2p orbitals must be in the same plane.

6. Conjugated dienes equilibrate between the s-cis and s-trans geometry, referring to the conformation of the single bond between the double bonds. The s-trans geometry predominates.

7. Absorbance of a photon by a molecule corresponds to promotion of an electron from a filled molecular orbital to an unfilled molecular orbital. In the visible region, this usually involves pi bonding and antibonding molecular orbitals, and conjugation increases wavelength of absorption. Molecules appear to our eye to be a combination of the wavelengths reflected (not absorbed).

8. The greater the number of pi bonds in conjugation, the smaller the energy difference between filled and unfilled orbitals, so the longer the wavelength of light that is absorbed (wavelength is inversely proportional to energy of light). That is why carrots are orange, for example.

Homework:

Read: Sections 20.4, 20.5 and 21.1-21.5 in the ebook textbook. This text is part of the Longhorn Textbook access program.

Take the Daily Quiz 17 before 10 PM tomorrow. Click here to access the quiz.

Start working on the Homework Problem Set 9, due at 10 PM on Monday, April 8. Click here to access the Homework Problem Set 8. This IS ALSO AN IMPORTANT ONE!! We will be grade it for completion only. It will teach you how to use KRE's to solve synthesis problems! Like last week, there is no Aktiv learning portion of this homework, just Gradescope.