Download Exam 2 Review A

110a Exam 3 Review Sheet—Fall Semester 2009
Review Session: Wednesday, October 14, 7:00 PM, SN Aud
Exam 3: Friday, October 16, 8:00 AM, SN Aud
Chapter 6:
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7.
You should be able to predict the products of a given reaction, based upon an understanding of the reaction
mechanisms (i.e., SN1 or SN2 or E1 or E2) operative for a given electrophile, nucleophile, and reaction
conditions (solvent and temperature). [table 6.7] You should be able to work in the reverse direction:
given a compound, what conditions and starting materials would you choose in order to synthesize it in high
yield.
You should be familiar with the detailed mechanisms of the SN1 and SN2 reactions. Rate determining
steps are important to consider, as are the transition states associated with these steps. Compare and
contrast the SN1 and SN2 reactions with respect to kinetics, nature of the electrophile [structure of
electrophile, nature of leaving group- halogens or sulfonate esters], nature of the nucleophile [recall protic
vs aprotic effects for SN2 here], optimal solvent for each, and the stereochemical outcome of each.
Carbocation structure and trends in stability. Hyperconjugation and inductive effects. Carbocations can do
three things: 1. React with nucleophiles, 2. -eliminate (lose H+) to form an alkene, 3. undergo skeletal
rearrangements via 1,2-hydride shifts or 1,2-methanide shifts. [we will defer discussion of #3 until Chapter
7]. Remember, carbocation stability plays a role in analyzing transition states, which can often allow us to
predict product ratios (most reactions climb the shortest hill). The Hammond-Leffler postulate is a useful
tool for correlating T-state structure (reactant-like or product-like) with exothermicity or endothermicity.
If you see a nucleophile and an electrophile on the same molecule, form a ring via an intramolecular
reaction. If you need to synthesize a ring, work backwards using the same logic!
You should be able to identify and define a solvolysis SN1 reaction, and be familiar with the
mechanism of E1 elimination which can happen at higher temperatures.
Synthetic utility of the SN2 reaction: you can now propose syntheses of halides, azides, esters, nitriles,
ethers, thioethers, alcohols,and thiols. Acetylene derivatives can be deprotonated and reacted with
electrophiles to form extended carbon chains.
DDT and methyl iodide. Do you know their ‘in the news’ stories?
Chapter 7:
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Rules for nomenclature of alkenes, cycloalkenes, and alkynes. Cis and trans, E and Z.
Hydrogenation of alkynes with P-2 or Lindlar catalyst. Role of catalyst, cis mode of addition.
Synthesis of trans alkenes via treatment of alkynes with Li metal in ammonia (dissolving metal
reduction). Mechanism of reaction.
Trends of stability of alkenes. We discussed this in terms of heats of hydrogenation, book also
mentions heats of combustion- be familiar with this analysis.
Synthesis of alkenes via E2 elimination. Mechanism of reaction and T-state structure. What evidence
supports the transition state structure? Zaitsev’s rule and T-state analysis to explain the origin of the rule.
Hofmann rule for E2 elimination with hindered strong base. Structural origin of rule.
Acid-catalyzed E1 dehydration of alcohols to synthesize alkenes. Mechanism of reaction. Reasons for ease
of dehydration 3°>2°>1°. Carbocation intermediates and the issue of carbocation rearrangements.
Synthesis of alkenes and alkynes: be familiar with the methods (reagents) and mechanisms (electron
pushing).