CHEM 2423 Unit 8 Homework Answers

Transcription

1 1 CEM 2423 Unit 8 omework Answers 1. Show the mechanism of the following reaction. Label the rate-limiting step. Draw the potential energy diagram for this reaction. (c) Explain the regiochemistry of this reaction. Why was 1-bromo-2-methylcyclohexane not formed? - - (RDS) -

2 2 (c) Formation of 1-bromo-2-methylcyclohexane would result from anti-markovnikov addition. o This does not occur because the intermediate carbocation formed in the RDS would be 2. o Formation of a 2 cation requires more energy than formation of a tertiary cation. ence, the pathway with the lower activation energy is favored. 2. For the following reactions involving addition of hydrogen halides, stereochemistry of the products may be significant. n each case, indicate if the product(s) are chiral or achiral, and whether the product mixture is optically active or optically inactive. C C 2 achiral optically inactive achiral optically inactive C 2 C 2 * C C 2 C 2 C 2 achiral optically inactive chiral racemic mixture optically inactive (c) * * * * achiral chiral chiral 50:50 mixture of diastereomers optically active

3 3 3. Show the mechanism that explains the following results. - 2 o cation - 3 o cation 4. Show the mechanism of reaction for each of the following. Label the rate-limiting step. Show stereochemistry, when appropriate. 2 2 S 4 Stereochemistry is not necessarily important in this reaction. f a new chiral center is formed, enantiomers would result. 3 2 (RDS) 2 2

4 enantiomer Stereochemistry is important here. llustration of anti-addition is part of the mechanism. - - (RDS) - (c) C C 2 C 2 Stereochemistry is also important here. t s a bit trickier to show in this case, because the two groups being added ( and ) are not the same, like in the previous problem. C 2 - (RDS) C 3 C 2 C 2 -

5 5 C 2 C C 2 2 C 2 C 2 C 2 C 2 C 2 3 (d) RR Stereochemistry is not important in this reaction only regiochemistry. owever, for you stereochemistry nuts since two new chiral centers are produced, this reaction would yield a total of 4 stereoisomers. chain initiating R-R 2 R 2 R - R -

6 6 chain propagating (RDS) - 5. Show the mechanism that explains the following results. C C 2 C 3 C C C C minor major C C 2 C 3 C C 2 (RDS)

7 7 2 C C 2 C C 2 2 o cation C C C C 3 o cation 2 C C 2 2 C C 6. Show all products of the following reactions. Label major and minor products, as necessary. Show stereochemistry, as necessary.

8 8 (c) C C C C 2 (d) C C RR C C (e) 2 2 S 4 (f) B 3 TF (2) 2 2, - (g) 2 2 S 4 C 2 C 2 (h) 2

9 9 (i) 2 2 (j) 2 2 (k) 2 Pt (l) C 3 (m) C 3 (1) 3 (n) C 2 C C C (2) Zn, 2 3 C 2 C C

10 10 (o) (1) 3 (2) Zn, 2 2 C C 2 C (1) 3 (p) C C 3 C C 2 C C 2 C (2) Zn, 2 3 C= =CC 2 C= =C 2 7. Write the reagents needed to achieve the following transformations. (1) 3 (2) Zn, 2 =CC 2 C 2 C 2 C= C=C 2 C (c) 2 Rh (d) C=C 2 RR C 2 C 2 (e) C=C P 4 C (f) C=C 2 (1) B 3 TF (2) 2 2, - C 2 C 2 (g) C C C C 2 (h) C C 2 2 C C 2

11 11 (i) RC 3 8. Show the structure of the alkenes that would produce the following compounds by ozonolysis. C ( ) 2 CC= C CC( ) 2 2 C= C 2 (c) C 2 C= only C 2 C CC 2 9. Show the structure of the intermediate (organoborane) that would form when a borane (let s say R 2 B) reacts with 2-methylbut-2-ene. the least substituted C gets the largest group - boron R 2 B R 2 B organoborane

12 Suggest a sequence of reactions suitable for preparing each of the following compounds from the indicated starting material. You may use any necessary organic or inorganic reagents. 1-propanol from 2-propanol 2 S 4 B 2 6, diglyme (2) 2 2, - 1-bromopropane from 2-bromopropane KEt Et RR (c) 1,2-dibromopropane from 2-bromopropane KEt 2 Et C 3 (d) 1-bromo-2-propanol from 2-propanol 2 S (e) 1,2-epoxypropane from 2-propanol 2 S 4 RC 3 (f) 2-methyl-2-propanol from 1-bromo-2-methylpropane t-buk t-bu 2 2 S 4 (g) t-butyl iodide from 1-iodo-2-methylpropane

13 13 t-buk t-bu (h) trans-2-chlorocyclohexanol from chlorocyclohexane KEt Et 2 2 (i) iodocyclopentane from cyclopentane 2 light & Na acetone (j) trans-1,2-dichlorocyclohexane from cyclohexane 2 light & KEt Et 2