Alkyl Halides and Elimination Reactions

Draw the structure of a dihalide that could be used to prepare each alkyne. There may be more than one possible dihalide.

a.

b.

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 mechanisms—${\mathbf{\text{S}}}_{\mathbf{\text{N}}}{\mathbf{\text{1, S}}}_{\mathbf{\text{N}}}\mathbf{\text{2}}$, E1, or E2—are 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 ${\mathbf{\text{CH}}}_{\mathbf{3}}\mathbf{\text{OH}}$ to ${\mathbf{\text{(CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{)}}}_{\mathbf{\text{2}}}\mathbf{\text{SO}}$.

e. The reaction rate depends on the concentration of the alkyl halide only.

f. The mechanism is concerted.

g. The reaction of ${\mathbf{\text{CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{CH}}}_{\mathbf{\text{2}}}\mathbf{\text{Br}}$ 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.

b.

c.

d.

e.

f.

g.

h.

What is the major product formed when each alkyl halide is treated with each of the following reagents: [1] ${\mathbf{\text{NaOCOCH}}}_{\mathbf{\text{3}}}$ ; [2] ${\mathbf{\text{NaOCH}}}_{\mathbf{3}}$;  [3]${\mathbf{\text{KOC(CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{)}}}_{\mathbf{\text{3}}}$ ? 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.

b.

c.

Draw all products, including stereoisomers, in each reaction.

a.

b.

c.

d.

Draw all of the substitution and elimination products formed from the given alkyl halide with each reagent: (a) ${\mathbf{\text{CH}}}_{\mathbf{3}}\mathbf{\text{OH}}$; (b) KOH. Indicatethe stereochemistry around the stereogenic centers present in theproducts, as well as the mechanism by which each product is formed.

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.

b.

c.

d.

Draw a stepwise, detailed mechanism for each reaction.

a.

b.

Draw the major product formed when (R)-1-chloro-3-methylpentane is treated with each reagent: (a) ${\mathbf{\text{NaOCH}}}_{\mathbf{\text{2}}}{\mathbf{\text{CH}}}_{\mathbf{\text{3}}}$ ; (b) KCN; (c) DBU.

Draw a stepwise, detailed mechanism for the following reaction.

Explain why the reaction of 2-bromopropane with ${\mathbf{\text{NaOCOCH}}}_{\mathbf{3}}$ gives ${\mathbf{\text{(CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{)}}}_{\mathbf{\text{2}}}{\mathbf{\text{CHOCOCH}}}_{\mathbf{\text{3}}}$ exclusively as product, but the reaction of 2-bromopropane with  ${\mathbf{\text{NaOCH}}}_{\mathbf{\text{2}}}{\mathbf{\text{CH}}}_{\mathbf{\text{3}}}$ gives a mixture of  ${\mathbf{\text{(CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{)}}}_{\mathbf{\text{2}}}{\mathbf{\text{CHOCH}}}_{\mathbf{\text{2}}}{\mathbf{\text{CH}}}_{\mathbf{\text{3}}}$ (20%) and  ${\mathbf{\text{CH}}}_{\mathbf{3}}{\mathbf{\text{CH=CH}}}_{\mathbf{2}}$ (80%).

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

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.

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

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.

b.

(a) Draw all products formed by treatment of each dibromide (A and B) with one equivalent of ${\mathbf{\text{NaNH}}}_{\mathbf{2}}$ . (b) Label pairs of diastereomers and constitutional isomers.