Topic 33: Substitution mechanisms - unimolecular vs. bimolecular

33.1What does concerted mean in the context of mechanistic steps?
 
33.2What do SN1 and SN2 stand for?
 
33.3Why must an SN1 reaction involve at least two mechanistic steps, by definition?
 
33.4Why is it particularly common for an SN1 reaction to involve three mechanistic steps?
 
33.5What are three characteristics of an SN1 reaction?
 
33.6What are three characteristics of an SN2 reaction?
 
33.7How are p atomic orbitals involved in both SN1 and SN2 mechanisms? (In which mechanism is the p orbital empty, and in which is it full?)
 
33.8Why are SN1 reactions prone to producing mixtures of several products?
 
33.9Why is it much less likely for a reaction with an SN2 mechanism to produce a mixture than one with an SN1 mechanism?
 

Topic 34: Substitution - Factors influencing substitution processes - the organic reactant

34.1Why are SN1 reactions never observed for primary alkyl halides?
 
34.2Why are SN2 reactions never observed for tertiary alkyl halides?
 
34.3What does the stability of carbocations have do with the preference for SN2 and SN1 reaction at primary and tertiary carbons, respectively? (And why is there this difference in stability in the first place?)
 
34.4What does steric hindrance have to do with the preference for SN2 and SN1 reaction at primary and tertiary carbons, respectively?
 
34.5What is the order of reactivity of alkyl halides going down the periodic table - F, Cl, Br, I? How do you explain that?
 
34.6Why are vinyl halides and aryl halides never involved in SN1 or SN2 reactions?
 

Topic 35: The Hammond Postulate

35.1What was George Hammond's postulate?
 
35.2How does the Hammond postulate relate to comparisons of endothermic and exothermic mechanistic steps?
 
35.3Why might the Hammond postulate be useful in discussions of organic reaction mechanisms?
 
35.4How is the Hammond postulate applicable in a discussion of substitution reactions?
 
35.5What makes the Hammond postulate a postulate and not a law?
 

Topic 36: Substitution - Factors influencing substitution processes - the nucleophile

36.1 How are basicity and nucleophilicity related to thermodynamics and kinetics?
 
36.2What characterizes a “good” nucleophile? Examples?
 
36.3Why are negatively charged nucleophiles (Cl–, CN–, RC≡C–) generally more reactive than neutral nucleophiles, such as H2O, CH3OH, NH3)?
 
36.4Why are negatively charged species rarely the nucleophile in SN1 reactions?
 
36.5What is solvolysis? Which mechanism, SN1 or SN2, is it more closely associated with? Why?
 

Topic 37: Substitution - Factors influencing substitution processes - the solvent

37.1What does aprotic mean?
 
37.2What are several examples of protic and aprotic solvents?
 
37.3Why might the choice of an aprotic solvent make an SN2 reaction more likely to happen, whereas choice of a protic solvent would slow it down?
 
37.4Why is it common to use protic solvents for SN2 reactions even though they are not as “good” solvents for that type of reaction?
 
37.5Why does the order of reactivity of halide nucleophiles reverse in going from a protic to aprotic solvents?
 
37.6What is the “catch” in relation to using protic solvents in SN1 reactions?
 
37.7Why is a protic solvent necessary for a solvolysis reaction?
 

Topic 38: Elimination - Alkenes

38.1What constitutes a β-elimination reaction?
 
38.2What are the three types of disubstituted alkenes?
 
38.3Why do we classify cis and trans isomers as diasteriomers?
 
38.4What is the trend in stability of alkenes, based on substitution (mono, di, tri, tetra)?
 
38.5What is the general “explanation” for this trend (using Google)? Is this the explanation your author gives?
 
38.6What is hyperconjugation, and how might it explain the trend in stability of substituted alkenes?
 

Topic 39: Elimination - The E2 mechanism

39.1What are the essential features of the E2 mechanism? Why “2” here?
 
39.2What special alignment of atoms is necessary for (or at least, strongly favors) an E2 mechanism?
 
39.3Besides strong RO– bases, what nitrogen-containing weak bases are popular for effecting E2 reactions? Your author may refer to these as strong bases, but technically they are not strong bases; all amines are weak bases.]
 
39.4Which nitrogen atom of DBN accepts the proton? Why this one and not the other?
 
39.5What is so special about DBN and DBU? [HINT: What makes them poor nucleophiles? And what does that have to do with this question?]
 
39.6Which solvent - nonpolar, polar aprotic, or protic - best promotes E2 reactions? Why?
 
39.7What do these abbreviations stand for: DMF, DMSO?
 
39.8If you needed to carry out an E2 reaction in the lab, why would you perhaps not choose DMSO as a solvent for the reaction? (two good reasons)
 

Topic 40: Elimination - the Zaitsev Rule and reaction selectivity

40.1What is the Zaitsev/Saytzeff/Zaitseff Rule?
 
40.2Why can't people seem to agree on how to spell Zaitsev's name?
 
40.3When does the Zaitsev Rule apply? When does it not?
 
40.4What does it mean for a reaction to be regioselective?
 
40.5What does it mean for a reaction to be stereoselective?
 

Topic 41: Elimination - The E1 mechanism

41.1What are the principal characteristics of the E1 mechanism?
 
41.2How it is related to the SN1 mechanism?
 
41.3Can you draw a proper energy diagram (meaning, fully mass-balanced, with energy arrows pointing in the correct direction) for the E1 elimination of isopropyl iodide reacting with water?
 
41.4Why is it safe to say that the base in an E1 reaction is almost always just the solvent itself?
 
41.5Why is it safe to say that a reaction involving an E1 mechanism is certain to give a mixture of several products?
 
41.6For what two types of alkyl halides is the E1 mechanism never observed?
 
41.7Given a 2o alkyl halide, what sorts of things can we do to avoid a reaction proceeding by the E1 or SN1 mechanism?
 
58 questions
364 questions for Organic I

364 Questions for Organic I

Dearest Student. This web page is a set of questions I call Detailed Intended Learning Outcomes For Organic Chemistry (Part I). Some time ago I asked myself, "Bob, what do you think are the key questions that you hope students will be able to answer after taking Chemistry 247 at St. Olaf College?" So here you have them. Some are very simple; some require more thought. All are good questions to be thinking about as you read, discuss, and master the practical aspects of organic chemistry. They are discussion starters and review tips. There are no answers here (though there are some clues). The questions are here to help you focus on what's important (to me, at least!) and organize your learning process. The questions are grouped into topics. Bite-size chunks. Take them a few at a time. Don't feast on them all at one sitting!

(preliminary version 2021.01.15 feeback: Bob Hanson)