Rules of the Day
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: 3. There are two possible arrangements of four different groups around a tetrahedral atom. The two different arrangements are mirror images of each other, a property referred to as chirality and often compared to handedness.
1. The two possible chair forms of cyclohexane can convert into each other rapidly at room temperature via boat like intermediates. During this interconversion the axial positions are switched to equatorial, and vice versa.
2. Groups larger than H prefer to be equatorial because when they are axial there is steric strain (also called non-bonded interaction strain or 1,3 diaxial interactions) with the other axial groups.
3. Larger groups on chair cyclohexanes have a greater preference for being equatorial, since large groups cause greater atom "crunching" (non-bonded interaction strain).
4. When converting a flat cyclohexane representation (wedges and dashes) or a Haworth projection to identify the more stable three-dimensional chair structure draw both, remembering that UP is UP and DOWN is DOWN and that the more stable chair has more large groups equatorial.
5. Look at the web handout on stereochemistry (click here for a copy) to help with definitions
6. Chiral objects (or molecules) cannot be superimposed upon their mirror image.
7. An object or molecule is not chiral if it contains a plane of symmetry or a center of symmetry.
8. An enantiomer is any molecule that cannot be superimposed on its mirror image (it does not have a plane or center of symmetry).
9. Diastereomers are molecules that are stereoisomers but not enantiomers; a situation that arises when there are more than one chiral center in the same molecule.10. Tetrahedral atoms such as carbon with four different substituents are chiral and are called chiral centers.
HOMEWORK:
Read: Sections 3.1 and 3.2 in the ebook textbook. This text is part of the Longhorn Textbook access program.
Take the Daily Quiz 6 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 4, due at 10 PM on Tuesday, September 24. Click here to access the Homework Problem Set 3. Note there are Aktiv Learning and Gradescope Questions, and you MUST DO BOTH. Collectively, homeworks count for 10% of your final course grade. The Aktiv Learning homework provides multiple attempts and provides feedback. It is intended to help you prepare for the Gradescope Questions, so we recommend you do the Aktiv Learning questions first.