1. (16 pts) Draw an accurate Lewis structure, on the line provided, for each of the molecules below. Please use lines to represent bonding electron pairs. Indicate all unshared electrons and formal charges.
3. (16 pts) Draw both chair conformations of cis-1-isopropyl-2-methylcyclohexane. Label all substituents (other than hydrogen) as axial (ax) or equatorial (eq). If one conformation is more stable than the other, circle it and, in one sentence, explain why.
4. (16 pts) Draw Newman projections of both the
most
stable and least stable conformations of 1-chlorobutane. You
are to sight down the C1-C2 bond (i.e. C1
in front, C2 behind it).
7. (15 pts) Consider the four acetic acid derivatives in the box, along with the pKa values under each molecule.
b. How do you know? It has the lowest pKa value
c. Why is it the strongest acid? The three Cl atoms withdraw electrons from the O-H bond via an inductive effect
d. Each acid above has an associated conjugate base. In the box, draw the structure of the second strongest conjugate base.
e. Using the weakest acid, draw appropriate resonance contributors to illustrate why its conjugate base is so stable:
f. What is the correlation between the strength of an acid and the stability of its conjugate base, and why does this correlation exist?
The more stable the conjugate base, the stronger the acid. This is because loss of a proton leaves an anion, and the more stable this anion is on its own, the more likely the proton is to leave it.
Bonus (5 pts, no partial credit possible) Two common acid functional groups are carboxylic and sulfonic acids. Which of these is more acidic than the other, and why is this?
As seen below, the conjugate
base of sulfonic acids is stabilized via three resonance contributors,
while that of carboxylic acids is stabilized by only two. Thus, the
negative charge in the sulfonic case is more delocalized (more "spread
out"), and is thus more stable, making the corresponding acid stronger.
