1. Rank the following compounds in the trend requested. (15 points each) a. Rank by nucleophilicity. The strongest nucleophile is 1, while the weakest nucleophile is 5. C 3 PNa (C 3 ) 3 C C 3 Na C 3 C 2 Na C 3 NNa 1 5 3 4 2 b. Rank by bond dissociation energy. Consider the bond dissociation energy for the C- bond indicated. The C- bond with the lowest bond dissociation energy (bond requiring the least amount of energy to break) is 1, while the C- bond with the highest bond dissociation energy is 5. 5 1 3 4 2 c. Rank by N 2 reactivity. Consider the rate of N 2 reaction for each substrate. The substrate that reacts the fastest in a N 2 reaction is 1, while the substrate that reacts the slowest is 5. I 4 2 1 3 5
2.(12) There are four isomers (A-D) that contain a benzene group with a methyl group attached para to a C 4 9 substituent. Para refers to when two substituents are placed 1,4 relative to each other on a benzene ring (similar to the structure shown). The C 4 9 substituent can have four different constitutional isomers thus yielding the four isomers A-D. In order to distinguish the four isomers a chlorination reaction ( 2, hν) was performed on each and the number of products obtained for monochlorination for each compound was determined. Compound A yielded 2 monochlorinated products, compound B yielded 4 monochlorinated products, and compounds C and D both yielded 5 monochlorinated products. To differentiate compounds C and D, it was determined that compound C has two 2 hydrogens, while compound D has six 2 hydrogens. Draw the structures for compounds A-D in the appropriate space. C 4 9 Compound A Compound B Compound C Compound D b.(12) Indicate the monobrominated product obtained if compounds A-D are reacted with 2 and hν. 2 2 2 2 c.(4) d.(4) Which compound (A-D) reacts the fastest in a bromination? C, generates 3 radical in resonance Which compound (A-D) reacts the slowest in a bromination? A, generates 1 radical in resonance
3. Indicate the major product for the following reactions. (7 points each) a. C 3 Na E2, strong base with 3 alkyl halide b. I Na N 2, intramolecular reaction c. C 3 K C 3 C 3 N 1, 3 alkyl halide with no adjacent hydrogens for elimination d. C 3 Na C 3 N 2, 2 alkyl halide with good nucleophile/weak base e. 2 obtain most stable 3 radical in resonance f. C 3 Na E2, strong base with 2 alkyl halide need anticoplanar elimination
g. C 3 C 3 Na 3 C C 3 C 3 C 3 N 2, good nucleophile/weak base h. C 3 AgN 3 C 3 N 1, rearrange carbocation i. 1) 2, 2) NaCN NC N 2 after halogenation j. Na N 2, good nucleophile/weak base k. C 3 Na E2, strong base with 2 adjacent to quarternary, need anticoplanar l. NaN 3 N 3 F F N 2, react at 2 bromide
4. Consider the following two-step reaction sequence. The first step is a bromination reaction, while the second step is a N 2 reaction. Answer the following rate questions by simply writing either faster, slower, or no change for each part. 2 NaC C 3 3 C 3 A B C a.(8) What would happen to the rate of each step if propane (A) is changed to 2- methylpropane? tep 1: tep 2: faster, obtain 3 radical in halogenation slower, N 2 reaction does not occur at 3 site b.(8) tep 1: tep 2: What would happen to the rate of each step if propane (A) is changed to ethane? slower, 1 radical obtained in halogenation faster, N 2 reactions are faster with less steric hindrance c.(8) What would happen to the rate of each step if 2 is changed to I 2? tep 1: tep 2: slower, iodination is slower than bromination faster, iodine is better leaving group in N 2 than bromine d.(5) What would happen to the rate of the second step if the solvent is changed from methanol (C 3 ) to acetonitrile (C 3 CN)? The rate would be FATER. Acetonitrile is an aprotic solvent, which will not hydrogen bond with nucleophile in N 2 reaction.
5. When an alcohol is reacted with bromide a different product is obtained depending upon whether acidic () or basic (Na) conditions are used. No reaction occurs under one set of conditions but a substitution occurs under the other. a.(5) Which conditions will allow a substitution to occur? (write acidic or basic) ACIDIC b.(5) What is the leaving group under this set of conditions? Water ( 2 ) Need to protonate alcohol first to make a good leaving group (hydroxide is a PR leaving group for N 2 reaction. c. In order to convert an alcohol into a better leaving group, the group can be reacted with a tosyl chloride to yield what is called a tosylate compound as shown. R Et 3 N Which of these compounds will react with potassium ethoxide with the fastest rate in a N 2 reaction? (Circle the substrate that would react the fastest) (5) R d.(12) The experiments shown below were carried out in 1935 as a way to understand the mechanism of the N 2 reaction. Indicate the product obtained under each set of conditions. 1) Et 3 N 2) C 3 C 2 K 1) Na 2) C 3 C 2
6. The cis and trans isomers of 1-bromo-4-tert-butylcyclohexane react at different rates with KC(C 3 ) 3 to yield the same mixture of enantiomers A and B. ( 3 C) 3 C ( 3 C) 3 C cis-1-bromo-4-tert-butylcyclohexane trans-1-bromo-4-tert-butylcyclohexane a.(8) Draw the structures of compounds A and B. ( 3 C) 3 C ( 3 C) 3 C Compound A Compound B b.(5) faster) c.(5) Which isomer (cis or trans) reacts faster with KC(C 3 ) 3? (circle the isomer that reacts CI TRAN Explain WY either cis or trans reacts faster. In the cis isomer, the bromine is in an axial position in the lowest energy conformation to allow the anticoplanar elimination to occur. d.(10) When NaC 3 is reacted with cis-1-bromo-4-tert-butylcyclohexane the major product is C, whereas the major product of NaC 3 reacting with trans-1-bromo-4-tert-butylcyclohexane is D. Draw the structures of compounds C and D. ( 3 C) 3 C C 3 ( 3 C) 3 C C 3 Compound C Compound D btain inversion of configuration during N 2 reaction. e.(5) Which isomer (cis or trans) reacts faster with NaC 3? CI TRAN