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: 8. Reactions will occur if the products are more stable than the reactants (motive) and the energy barrier is low enough (opportunity).10. A reaction mechanism describes the sequence of steps occurring during a reaction. 11. Most bond-making steps in reaction mechanisms involve nucleophiles reacting with electrophiles.
1. Trans alkenes are more stable than cis alkenes because cis alkanes have some non-bonded interaction strain. In addition, more highly substituted alkenes are more stable than less substituted alkenes (we don't really tell you why, just learn it please)
2. Alkenes react with H-X (X = Cl, Br, I) in a mechanism that involves initial protonation of the pi bond (add a proton) to give a carbocation intermediate, that then adds X- (make a bond between a nucleophile and electrophile) to give an haloalkane (alkyl halide). Click here to see the reaction movie of H-Br adding to propene.
3. Reactions are like crimes, they need motive and opportunity.
4. Heating up a reaction increases the rate by increasing the number of molecules with enough energy to get over an energy barrier.A. A reaction has a motive if the products are lower in energy than the starting materials. That is, stronger bonds are made than broken in the reaction, and/or a weaker acid/weaker base is produced, and/or entropy is increased through the creation of a small gaseous fragment. Motive (also called thermodynamic driving force) determines position of equilibrium.
B. A reaction has an opportunity to take place if the mechanism contains no species that are higher in energy than the energies of a resonable fraction of starting material molecules at a given temperature. Opportunity determines rate of a reaction (also called reaction kinetics).
5. In mechanisms, arrows are used to indicate movement of electrons.
6. Arrows never indicate movement of atoms directly.
7. Arrows always start at an electron source and end at an electron sink. An electron source is a pi bond, lone pair, or bond that can break to avoid overfilling a valence, and an electron sink is an atom that can accept a new bond, often with a full or partial positive charge.
8. Breaking a bond will occur to avoid overfilling valence at the electron sink atom.
9. A nucleophile contains an electron rich pi bond or lone pair that is the electron source for a bond forming process. Analogous to a Lewis base.
10. An electrophile contains an electron deficient atom that serves as the electron sink in a bond forming process (Analogous to a Lewis acid) or possesses a weak bond that breaks to make a stable ion or fragment..
11. Most organic mechanisms are composed of only four different mechanistic elements, so that predicing mechanisms often comes down to a fourway multiple choice for each step. (Note these statements are written from the point of view of the carbon containing reactant, i.e. the alkene)A. Make a bond between a nucleophile (electron rich species with an electron source like a pi bond or lone pair) and an electrophile (electron deficient species that has an electron sink atom).
B. Break a bond to create stable molecules or ions
C. Add a proton
D. Take a proton away
HOMEWORK:
If you have not already, you must Watch the Terpene video. You are responsible for this information for the next midterm!
Read: Section 6.4B,C in the eBook.
Take the Daily Quiz 10 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 5, now due at 10 PM on Wednesday, October 9. Click here to access the Homework Problem Set 5. 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.