Draw the alkynes formed in each reaction. Two equivalents of each base are used. a. C C

Label the and carbons in each alkyl halide. Draw all possible elimination products formed when each alkyl halide is treated with K+ OC(CH3)3. a. CH3CH2CH2CH2CH2Cl b. Cl c. Br

Classify each alkene in the following vitamins by the number of carbon substituents bonded to the double bond. a. vitamin A OH b. vitamin D3 CH2 H HO

For which alkenes are stereoisomers possible? a. b. CH3CH2CH CHCH3 c. CH CH

Label each pair of alkenes as constitutional isomers, stereoisomers, or identical. a. and c. C C and C C CH3CH2 H H CH3 CH3CH2 CH3 HH b. and d. C C and C C H H CH3CH2 H CH3CH2 CH3 3 HCH

Which alkene in each pair is more stable? a. or c. CH3 CH3 or b. C C or CH3CH2 CH2CH3 HH C C CH3CH2 CH2CH3

While cis- and trans-2-butene differ in stability by only 3 kJ/mol, cis- and trans-2,2,5,5-tetramethyl3-hexene differ in stability by 44 kJ/mol. Explain why the difference in the stability of the second pair of alkene stereoisomers is so much larger.

Several factors can affect alkene stability. Explain why alkene A is more stable than alkene B even though both contain disubstituted carboncarbon double bonds. A B

Use curved arrows to show the movement of electrons in the following E2 mechanism. Draw the structure of the transition state. OCH2CH3 (CH3CH2)3CBr (CH3CH2)2C CHCH3 + HOCH2CH3 + Br

Why is (CH3)3CCH2Br inert to an E2 elimination?

Rank the alkyl halides in each group in order of increasing reactivity in an E2 reaction. a. (CH3)2C(Br)CH2CH2CH3 (CH3)2CHCH2CH2CH2Br (CH3)2CHCH2CH(Br)CH3 b. Cl CH3 Cl Cl CH3

How does each of the following changes affect the rate of an E2 reaction? a. tripling [RX] d. changing the leaving group from I to Br b. halving [B:] e. changing the base from OH to H2O c. changing the solvent from CH3OH to DMSO f. changing the alkyl halide from CH3CH2Br to (CH3)2CHBr

What alkenes are formed from each alkyl halide by an E2 reaction? Use the Zaitsev rule to predict the major product. a. CH3 C CH3 H C H Br CH2CH3 b. CH3 CH3 Br c. Cl d. Cl CH3 CH3 CH3

Draw an E1 mechanism for the following reaction. Draw the structure of the transition state for each step. (CH3)2C CHCH3 + CH3OH2 + Cl

What alkenes are formed from each alkyl halide by an E1 reaction? Use the Zaitsev rule to predict the major product. a. CH3CH2 CH3 Cl C CH2CH3 b. CH3 I CH2CH2CH3

How does each of the following changes affect the rate of an E1 reaction? a. doubling [RX] d. changing the leaving group from Cl to Br b. doubling [B:] e. changing the solvent from DMSO to CH3OH c. changing the halide from (CH3)3CBr to CH3CH2CH2Br

Draw both the SN1 and E1 products of each reaction. a. CH3 Br + H2O b. CH3 CH3CH2OH CH3 CH2CH2CH3 Cl C

Draw the anti periplanar geometry for the E2 reaction of (CH3)2CHCH2Br with base. Then draw the product that results after elimination of HBr.

Given that an E2 reaction proceeds with anti periplanar stereochemistry, draw the products of each elimination. The alkyl halides in (a) and (b) are diastereomers of each other. How are the products of these two reactions related? Recall from Section 3.2A that C6H5 is a phenyl group, a benzene ring bonded to another group. a. C OCH2CH3 C H Br CH3 C6H5 C6H5 H b. CH3 C OCH2CH3

Explain why cis-1-chloro-2-methylcyclohexane undergoes E2 elimination much faster than its trans isomer.

Which mechanism, E1 or E2, will occur in each reaction? a. CH3 CH3 Cl CH3 C + OCH3 c. C(CH3)3 Cl + CH3OH b. I + H2O d. CH3CH2Br OC(CH3) + 3

Draw the alkynes formed in each reaction. Two equivalents of each base are used. a. C C Cl H Cl H CH2CH3 NH2 c. CH3 Br Br CH2CH3 NH2 C b. KOC(CH3)3 DMSO CH3CH2CH2CHCl2 d. Br Br NH2

Draw the products in each reaction. a. Cl K+ OC(CH3)3 c. CH2CH3 I CH3CH2OH b. CH3 H Cl CH2CH3 OH C d. Cl CH3CH2O

Draw a stepwise mechanism for the following reaction. CH3 Br CH3 CH3 CH3 + + HBr CH3OH CH3 OCH3 CH3

Draw all possible constitutional isomers formed by dehydrohalogenation of each alkyl halide. a. CH3CH2CH2CH2CH2CH2Br b. Br c. CH3CH2CHCHCH3 Cl CH3 d. I

What alkyl halide forms each of the following alkenes as the only product in an elimination reaction? a. CH2 CHCH2CH2CH3 b. (CH3)2CHCH CH2 c. CH2 d. CH3 e. C(CH3)3

Which double bonds in the following natural products can exhibit stereoisomerism? Farnesene is found in the waxy coating of apple skins and geranial is isolated from lemon grass. a. farnesene b. CHO geranial

Label each pair of alkenes as constitutional isomers, stereoisomers, or identical. a. CH3 and CH2 c. and b. CH3 CH3CH2 CH2CH3 CH3 C C and CH3CH2 CH3 CH3 CH2CH3 C C d. C H CH3 CH3 and C CH3 H CH3

PGF2 is a prostaglandin, a group of compounds that are responsible for infl ammation (Section 19.6). (a) How many tetrahedral stereogenic centers does PGF2 contain? (b) How many double bonds can exist as cis and trans isomers? (c) Considering both double bonds and tetrahedral stereogenic centers, what is the maximum number of stereoisomers that can exist for PGF2? OH HO PGF2 CH2CH CH(CH2)3COOH CH CHCH(OH)(CH2)4CH3

Rank the alkenes in each group in order of increasing stability. a. CH2 CHCH2CH2CH3 C H CH3CH2 H CH3 C C H CH3CH2 H CH3 C b. CH2 C(CH3)CH2CH3 CH2 CHCH(CH3)2 (CH3)2C CHCH3

H values obtained for a series of similar reactions are one set of experimental data used to determine the relative stability of alkenes. Explain how the following data suggest that cis-2-butene is more stable than 1-butene (Section 12.3A). + H2 + CH2 CHCH2CH3 CH3CH2CH2CH3 H = 127 kJ/mol H = 120 kJ/mol 1-butene cis-2-butene H2 CH3CH2CH2CH3 H CH3 CH

Draw all constitutional isomers formed in each E2 reaction and predict the major product using the Zaitsev rule. a. Cl (CH3)3CO c. OH I CH3 e. OH I b. O O Cl DBU d. Cl OC(CH3)3 f. Br OH

For each of the following alkenes, draw the structure of two different alkyl halides that yield the given alkene as the only product of dehydrohalogenation. a. (CH3)2C CH2 b. CH CH2 c.

Explain why (CH3)2CHCH(Br)CH2CH3 reacts faster than (CH3)2CHCH2CH(Br)CH3 in an E2 reaction, even though both alkyl halides are 2

Consider the following E2 reaction. Br OC(CH3)3 (CH3)3COH a. Draw the by-products of the reaction and use curved arrows to show the movement of electrons. b. What happens to the reaction rate with each of the following changes? [1] The solvent is changed to DMF. [2] The concentration of OC(CH3)3 is decreased. [3] The base is changed to OH. [4] The halide is changed to CH3CH2CH2CH2CH(Br)CH3. [5] The leaving group is changed to I .

Dehydrohalogenation of 1-chloro-1-methylcyclopropane affords two alkenes (A and B) as products. Explain why A is the major product despite the fact that it contains the less substituted double bond. 1-chloro-1-methylcyclopropane CI A K+ OC(CH3)3 B +

What is the major stereoisomer formed in each reaction? a. KOH CH3CH2CH2 C H Br b. Cl NaOCH2CH3

Draw all constitutional isomers formed in each elimination reaction. Label the mechanism as E2 or E1. a. Br OCH3 c. I OC(CH3)3 e. Cl OH b. CH3OH Br d. CH2CH2CH3 Cl CH3 H2O f. Cl OH

Rank the alkyl halides in each group in order of increasing E2 reactivity. Then do the same for E1 reactivity. a. Br Br Br b. CH3 Cl Cl Br CH3 CH3

Which elimination reaction in each pair is faster? a. CH3 Cl CH3 Cl OH OH b. Cl Cl H2O H2O c. H2O OH OH DMSO (CH3)3CCl (CH3)3CCl

In the dehydrohalogenation of bromocyclodecane, the major product is cis-cyclodecene rather than trans-cyclodecene. Offer an explanation.

Explain the following observation. Treatment of alkyl chloride A with NaOCH2CH3 yields only one product B, whereas treatment of A with very dilute base in CH3CH2OH yields a mixture of alkenes B and C, with C predominating. A B C Cl

What is the major E2 elimination product formed from each halide? a. H CH3 CH3 Br CH2CH3 C6H5 b. H CH3 CH3 Br CH2CH3 C6H5 c. CH3 H CH3 Br CH2CH3 C6H5

Taking into account anti periplanar geometry, predict the major E2 product formed from each starting material. a. Cl CH3 CH(CH3)2 b. Cl CH3 CH(CH3)2 c. D Cl D d. D C

a. Draw three-dimensional representations for all stereoisomers of 2-chloro-3-methylpentane, and label pairs of enantiomers. b. Considering dehydrohalogenation across C2 and C3 only, draw the E2 product that results from each of these alkyl halides. How many different products have you drawn? c. How are these products related to each other?

Which stereoisomercis- or trans-1-bromo-3-tert-butylcyclohexanewill react faster in an E2 elimination reaction? Offer an explanation.

Draw the structure of a dihalide that could be used to prepare each alkyne. There may be more than one possible dihalide. a. CH3C CCH3 b. CH3 CH3 CH3 C CHC c. C C

Under certain reaction conditions, 2,3-dibromobutane reacts with two equivalents of base to give three products, each of which contains two new bonds. Product A has two sp hybridized carbon atoms, product B has one sp hybridized carbon atom, and product C has none. What are the structures of A, B, and C?

For which reaction mechanismsSN1, SN2, E1, or E2are each of the following statements true? A statement may be true for one or more mechanisms. a. The mechanism involves carbocation intermediates. b. The mechanism has two steps. c. The reaction rate increases with better leaving groups. d. The reaction rate increases when the solvent is changed from CH3OH to (CH3)2SO. e. The reaction rate depends on the concentration of the alkyl halide only. f. The mechanism is concerted. g. The reaction of CH3CH2Br with NaOH occurs by this mechanism. h. Racemization at a stereogenic center occurs. i. Tertiary (3) alkyl halides react faster than 2 or 1 alkyl halides. j. The reaction follows a second-order rate equation.

Draw the organic products formed in each reaction. a. Br OC(CH3)3 e. CH2CH3 Br OC(CH3)3 h. Cl Cl KOC(CH3)3 (2 equiv) DMSO b. I OCH2CH3 f. Br CH2CH3 CH3CH2OH i. I CH3CH2OH c. Cl Cl CH3 CH3 NH2 (2 equiv) C g. (CH3)2CH CHCH2Br Br 2 NaNH2 j. Cl H2O d. Br DBU

What is the major product formed when each alkyl halide is treated with each of the following reagents: [1] NaOCOCH3; [2] NaOCH3; [3] KOC(CH3)3? If it is not possible to predict the major product, identify the products in the mixture and the mechanism by which each is formed. a. CH3Cl b. Cl c. Cl d. Cl

a. The cis and trans isomers of 1-bromo-4-tert-butylcyclohexane react at different rates with KOC(CH3)3 to afford the same mixture of enantiomers A and B. Draw the structures of A and B. b. Which isomer reacts faster with KOC(CH3)3? Offer an explanation for this difference in reactivity. c. Reaction of cis-1-bromo-4-tert-butylcyclohexane with NaOCH3 affords C as the major product, whereas reaction of trans-1-bromo-4-tert-butylcyclohexane affords D as the major product. Draw the structures for C and D. d. The cis and trans isomers react at different rates with NaOCH3. Which isomer reacts faster? Offer an explanation for the difference in reactivity. e. Why are different products formed from these alkyl halides when two different alkoxides are used as reagents?cis-1-bromo-4-tert-butylcyclohexane (CH3)3C Br trans-1-bromo-4-tert-butylcyclohexane (CH3)3C Br

Draw all products, including stereoisomers, in each reaction. a. Cl H OH c. C6H5 Cl CH3OH e. Br CH3 CH3COO b. H2O Cl H d. Cl NaOH f. D Br KOH

Draw all of the substitution and elimination products formed from the following alkyl halide with each reagent. Indicate the stereochemistry around the stereogenic centers present in the products, as well as the mechanism by which each product is formed. Cl a. CH3OH b. KOH

The following reactions do not afford the major product that is given. Explain why this is so, and draw the structure of the major product actually formed. a. CH3 Br CH3 OC(CH3)3 OC(CH3)3 c. Cl CH3 OH b. Br OCH3 d. Cl I

Draw the major product formed when (3R)-1-chloro-3-methylpentane is treated with each reagent: (a) NaOCH2CH3; (b) KCN; (c) DBU.

Draw a stepwise, detailed mechanism for the following reaction. H2O Br + ++ H H H H OH HBr H H H H OH

Explain why the reaction of 2-bromopropane with NaOCOCH3 gives (CH3)2CHOCOCH3 exclusively as product, but the reaction of 2-bromopropane with NaOCH2CH3 gives a mixture of (CH3)2CHOCH2CH3 (20%) and CH3CH CH2 (80%).

Draw a stepwise detailed mechanism that illustrates how four organic products are formed in the following reaction. CI HCI CH3OH OCH3 OCH3

Although there are nine stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane, one stereoisomer reacts 7000 times more slowly than any of the others in an E2 elimination. Draw the structure of this isomer and explain why this is so.

Explain the selectivity observed in the following reactions. O O H CH3 H Br CH3O CH3O O O H Br H CH3 O O H H O O H

Draw a stepwise mechanism for the following reaction. The four-membered ring in the starting material and product is called a -lactam. This functional group confers biological activity on penicillin and many related antibiotics, as is discussed in Chapter 22. (Hint: The mechanism begins with elimination and involves only two steps.) N S H N C6H5O C CH2Cl O O DBN N N C6H5O S O -lactam O O O

Although dehydrohalogenation occurs with anti periplanar geometry, some eliminations have syn periplanar geometry. Examine the starting material and product of each elimination, and state whether the elimination occurs with syn or anti periplanar geometry. a. SeOC6H5 D H D b. C CH3 CH3 H H Br Br C CH3 H CH3 H C C Zn