Rules of the Day CH320M/328M

Click here for a copy of my lecture notes from today's lecture

Click here for a copy of the handout used in class today

Featured Golden Rules of Chemistry: None today

1. For amides, pi delocalization overrides your prediction based on VSEPR and the N atom is sp2 hybridized because this allows for pi delocalization. Amides are important in biochemistry as the backbone of proteins, so it is worth noticing the special properties of this functional group. Click here to hear the amide song I played in class today.

2. Constitutional isomers are molecules with the same molecular formula but different connectivities between atoms.

3. To name alkanes according to IUPAC rules, you must memorize the alkane parent (main chain) names (Table 2.1) and alkyl group names (Tables 2.2 and 2.3). Then you must memorize the rules on the web handout, which explains all you need to know about alkane nomenclature. I apologize for all of the goofy names and this memorization, but there is no way around it as far as I know.

Click here to learn the alkane names with a song:

Country K-pop 70's Rock Rap

4. To get started, just pay attention to what the dude says: To name alkanes, number the groups so the first gets the lowest number, then list them alphabetically using "yl", followed by writing the parent chain ending in "-ane".

5. Energy and stability are related to each other, and they are both RELATIVE terms in organic chemistry, i.e. they are not absolute, but rather only make sense in the context of comparisons. A molecule with higher energy is less stable, and a molecule with lower energy is more stable. Strain of any kind raises energy and decreases stability in a molecule.

6. The C-C sigma bonds of alkanes rotate rapidly at room temperature, giving rise to conformational isomers.

7. The two extreme conformations in ethane are staggered (more stable) and eclipsed (less stable). Staggered is more stable due to minimized torsional strain (interactions between filled and unfilled orbitals). *** The notion that alkanes prefer to be staggered due to torsional strain is the key concept in molecular conformational analysis.***

8. The preferred staggered conformation of butane is the "anti" configuration, rather than the "gauche" conformations (the other staggered conformations of butane). The staggered anti conformation is favored due to steric strain also called nonbonded interaction strain (the atoms "crunch" into each other a bit in the gauche conformation).

9. Averaged over time, alkanes exist in the preferred "zig-zag" conformation, but on the picosecond (10^-12 sec) timescale they are rapidly vibrating, and these vibrations randomly lead to rotations. Watch the animations of ethane, butane, and octane to see how molecules move.

HOMEWORK:

Read: Sections 2.4-2.5 in the ebook textbook. This text is part of the Longhorn Textbook access program.

Take the Daily Quiz 5 before 10 PM tomorrow. Click here to access the quiz . These quizzes are designed to review the important material from today's lecture. Together, they will count as 3% of your final grade.

Finish working on the Homework Problem Set 2, due at 10 PM tonight Wednesday, September 9. Note there are Aktiv Learning and Gradescope Questions, and you MUST DO BOTH. Click here to access to the Aktiv Learning electronic homework system.

Click here to access Aktiv learning Homework Problem Set 2

Click here to access Gradescope Homework Problem Set 2

Start working on the Homework Problem Set 3, due at 10 PM Wednesday, September 16. Note there are Aktiv Learning and Gradescope Questions, and you MUST DO BOTH. Click here to access to the Aktiv Learning electronic homework system.

Click here to access Aktiv learning Homework Problem Set 3

Click here to access Gradescope Homework Problem Set 3