chem 233
Sample Exam 2 Posted
Tuesday--Nov 20, 2007 Filed in: 233
I posted a sample exam
for exam #2 on the shared files page
(233sample_ex2.pdf). You may work through this
example to help you study. I do not recommend relying
soley on this example; also look at homework
questions and TA notes for additional
material.
|
Stereoselectivity in E1
Monday--Nov 19, 2007 Filed in: 233
There have been several
questions about the stereoselectivity of an E1
elimination mechanism. Two arguments can be made.
A kinetic
argument compares the relative energies of
the carbocation intermediates leading to each
product. The carbocation intermediate on the left is
more stable than the carbocation intermediate on the
right due to reduced steric strain; therefore the
trans alkene is favored. Because this reaction is
reversible a thermodynamic
argument can
also be made and is actually more correct; although
the outcome is the same in this instance. Thus, the
trans alkene product is favored because it is more
stable (lower in energy) than the cis alkene. Trans
is more stable than cis for the same reason already
mentioned, less steric strain. Caution: thermodynamic
arguments (comparing relative stabilities of
products)
can only be made when reactions are reversible
(equilibrium). This reaction is reversible and
explains why distillation was necessary to remove the
alkene products and shift the equilibrium toward
products (LeChatleir principle).
Final Exam
Thursday--Nov 15, 2007 Filed in: 233
CHEM 233 final exam
will meet according to the schedule below. The exams
will start on time so please arrive early so that you
may find your seat. Again, a final exam information
sheet will be distributed on the day of your
practical. Happy Thanksgiving.
Monday-Thursday sections: Monday, Dec. 10, 6pm-7pm, Lecture Center B1.
Friday sections: Monday, Dec. 10, 6:15pm-7:15pm, Lecture Center A1.
Monday-Thursday sections: Monday, Dec. 10, 6pm-7pm, Lecture Center B1.
Friday sections: Monday, Dec. 10, 6:15pm-7:15pm, Lecture Center A1.
Weeks 14-16 Schedule
Monday--Nov 12, 2007 Filed in: 233
233 Final Exam Time
Monday--Nov 12, 2007 Filed in: 233
The final exam for CHEM
233 will be held on Monday, December 10 from 6-8pm in
Lecture Centers A1 and B1. Because there are two
rooms, the class will be divided in half. You will
receive an informational sheet on the day of your
practical exam that will indicate which Lecture
Center you should attend. This info sheet will also
contain sample questions, review topics as well as
exam policies.