2. (14 pts) For each of the following four molecules, list the properties from the list on the right which best describe it. Each item on the list can be used as often as necessary, or not at all. DON'T GUESS!!
1. (12 pts) Give acceptable names for the following compounds,
being sure to address alkene geometry and R/S configuration where appropriate.
2. (14 pts) For each of the following four molecules,
list the properties from the list on the right which best describe it.
Each item on the list can be used as often as necessary, or not at all.
DON'T GUESS!!
 |
a. forms the least stable carbocation upon
loss of bromide ion
b. SN1 reaction very facile c. contains no sp3 carbon atoms d. capable of E1 reaction to form an alkene e. whether SN1 vs. SN2 mechanism is solvent-controlled f. incapable of an elimination reaction g. completely planar (all atoms) h. SN2 reaction is essentially impossible i. SN2 reaction very facile j. reacts with bromine (uncatalyzed) k. capable of E2 reaction to form an alkene |
3. (30 pts) Complete the following reactions (provide
either the starting molecule, the reagent(s), or product(s). If more than
one product is produced, draw them all. If one product predominates, circle
it.
4. (16 pts) Indicate a synthesis of any TWO (2) of the
following four molecules from the indicated starting materials. You may
use any inorganic reagents you like, but all carbon atoms must come from
the starting materials provided. Please fill in the letter of your choices
in the spaces provided.
5. (16 pts) Explain the following observations.
a. p-Nitrophenol is about a thousand times more acidic than phenol (pKa values of 7.1 vs. 9.9, respectively). You must use resonance structures in your answer.
The conjugate base of phenol (A)
has several resonance structures, including B
and C.
Nitrophenol's conjugate base has the same resonance, except that the structure
in which the anionic charge is para (D)
allows the nitro group to afford additional stabilizaion by spreading out
the charge even more, via an additional resonance form, E.
As you know, the more resonance forms, the more stable the entity, and
the more stable the conjugate base, the more acidic the acid.
b. (R)-2-bromohexane, when treated with sodium bromide
in a nonpolar solvent, undergoes racemization at twice the rate
of SN2 reaction.
It's a secondary halide in a nonpolar solvent, making the displacement an SN2 process. A bromide is being displaced by another bromide, and, since it's SN2, it occurs with inversion of configuration. For every displacement, then, a pair of enantiomers is produced - one molecule that was inverted by the reaction, and one that underwent no change at all. Or, think of it another way - if only half the molecules in a given quantity of (R)-2-bromohexane reacted with Br-, then you'd have half S and half R molecules - or, the entire quantity was racemic!
6. (8 pts) Consider the reaction (diagrammed in the box)
of 1-bromo-1-methylcyclopentane with ethoxide in ethanol to form 1-methylcyclopentene
as the main product. It is likely that this reaction proceeds via both
E1 and E2 pathways - please outline both mechanisms.
The reaction diagrammed in the box is a well-known method for epoxide
synthesis. Provide a mechanism which details the epoxide-making (second)
step, and draw the structure of the epoxide produced.
