Ch. 8 - Elimination ReactionsWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

Solvents are (mostly) inert compounds that provide a medium for a reaction to take place in. 

Concept #1: General format of reactions and how to interpret solvents.

Although extremely important in lab, they rarely affect the outcome of a written reaction in Orgo 1. In fact, for the purposes of this course, I will usually have you ignore solvents in questions requiring you to predict mechanisms.

There are exceptions to the above reaction format. If reagents are numbered, several may be both above and below the arrow. However, many simple reactions do follow this format. 

Concept #2: The difference between protic vs. aprotic solvents.

Polar solvents are solvents which contain a net dipole.

  • Aprotic Solvents are solvents that cannot display hydrogen-bonding.
  • Protic Solvents are solvents that display hydrogen-bonding (this stabilizes carbocations, but hinders nucleophiles)
  • Therefore, we will prefer to run SN1 & E1 in protic solvents, and SN2 & E2 in aprotic solvents.

Example #1: Identify the following solvents as apolar, polar aprotic or polar protic. 

Example #2: Identify the following solvents as apolar, polar aprotic or polar protic. 

Example #3: Identify the following solvents as apolar, polar aprotic or polar protic. 

Example #4: Identify the following solvents as apolar, polar aprotic or polar protic. 

Example #5: Identify the following solvents as apolar, polar aprotic or polar protic. 

Example #6: Identify the following solvents as apolar, polar aprotic or polar protic. 

Example #7: Identify the following solvents as apolar, polar aprotic or polar protic. 

The structure in the video and below is actually DMA since it's chemical formula is CH3CON(CH3)2.

DMF would simply have an H instead of a CH3 coming off the carbonyl carbon to the left. Both would be considered polar aprotic solvents since no hydrogen bonding occurs.

Example #8: Identify the following solvents as apolar, polar aprotic or polar protic. 

Additional Problems
In which of the solvents below would the reaction shown take place at the fastest rate? CH3CH2CH2CH2Br   +   NaCN   →   CH 3CH2CH2CH2CN  + NaBr a) ethanol  b) acetic acid c) dimethyl sulfoxide d) water
Identify the correct potential energy diagram for a secondary alkyl bromide (2°RBr) undergoing an SN1 reaction in protic versus aprotic solvent. Provide rationale to support your choices. 
Which one of the following is a polar aprotic solvent?   A. DMSO B. DMF C. Acetone D. All the above
Which solvent would favor and SN2 style mechanism? A)  Methanol B)  Dimethyl formamide C)  Water D)  Acetic acid
Rank the following in order of nucleophilicity in polar protic solvents. (1 – least nucleophilic, 3 – most nucleophilic)
Which conditions favor an efficient nucleophilic substitution reaction on 2-chloro-2-methylpropane? a. A weak nucleophile in a polar protic solvent b. A weak nucleophile in a polar aprotic solvent c. A strong nucleophile in a polar protic solvent d. A strong nucleophile in a polar aprotic solvent e. A strong nucleophile in a nonpolar solvent
Which conditions favor an efficient nucleophilic substitution reaction on 1-chlorobutane? a. A weak nucleophile in a polar protic solvent b. A weak nucleophile in a polar aprotic solvent c. A strong nucleophile in a polar protic solvent d. A strong nucleophile in a polar aprotic solvent e. A strong nucleophile in a nonpolar solvent
Circle the only polar aprotic solvent:
Write “non-polar”, “polar aprotic”, or “polar protic” to describe each of the following solvents: 
For the following pairs of reactions, mark an “X” in the box on the right indicating which will go faster. The compound on top of the arrow is the solvent.
Circle “non-polar”, “polar aprotic”, or “polar protic” to describe each of the following solvents:  
What are the names and the structures of LDA, DMSO, and DMF?
What would be the effect of increasing solvent polarity on the rate of each of the following nucleophilic substitution reactions? (a) Nu: + R—L → R—Nu+ + :L-      
What would be the effect of increasing solvent polarity on the rate of each of the following nucleophilic substitution reactions? (b) R—L+ → R+ + :L      
Rank the species below in order of increasing nucleophilicity in hydroxylic solvents (weakest nucleophile first):  CH3CO2-, CH3S-, HO-, H2O. a) H2O  <  CH3S-  <  CH3CO2-  <  HO- b) H2O  <  HO-  <  CH3CO2-  <  CH3S- c) H2O  <  CH3CO2-  <  HO-  <  CH3S- d) CH3CO2 - <  H2O  <  HO-  <  CH3S-
Circle the strongest nucleophile in each category. a) Cl -    vs    Br -    (in EtOH)   b) CH3OH   vs    CH3SeH   c) NH2-     vs       CH 3-
The reaction of chloroethane with water in the gas phase to produce ethanol and hydrogen chloride has ΔH° = +26.6 kJ mol -1 and ΔS° = +4.81 J K-1 mol-1 at 25°C. (d) In aqueous solution the equilibrium constant is very much larger than the one you just calculated. How can you account for this fact?  
First, complete and balance each of the equations below. Then, choosing among ethanol, hexane, and liquid ammonia, state which (there may be more than one) might be suitable solvents for each of these reactions. Disregard the practical limitations that come from consideration of “like dissolves like” and base your answers only on relative acidities.
Dimethylformamide (DMF), HCON(CH3)2, is an example of a polar aprotic solvent, aprotic meaning it has no hydrogen atoms attached to highly electronegative atoms. (c) DMF, when used as the reaction solvent, greatly enhances the reactivity of nucleophiles (e.g., CN- from sodium cyanide) in reactions like this:  NaCN + CH3CH2Br → CH3CH2C≡N + NaBr Suggest an explanation for this effect of DMF on the basis of Lewis acid–base considerations. (Hint: Although water or an alcohol solvates both cations and anions, DMF is only effective in solvating cations.) 
Number the following in each series according to the attribute listed.
Which reagent in each pair listed here would be the more reactive nucleophile in a polar aprotic solvent? (a) CH3NH- or CH3NH2 
In each of the pairs, determine the better nucleophile in DMSO as a solvent:
Which of the following solvents can not be used with (CH3)3COK? a. (CH3CH2)2O b. (CH3)3COHc. H2O d. Liquid NH3 e. None of these
Which of the following is a protic solvent?