Complete the following reactions. If no reaction is likely,...

Complete the following reactions. If no reaction is likely, explain why. (a) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\mathrm{OH}+\mathrm{Na} \longrightarrow \stackrel{\mathrm{CH}_{3} \mathrm{I}}{\longrightarrow}$ (b) $\mathrm{CH}_{3} \mathrm{SH}+\mathrm{NaOH}_{(1 \text { equiv. })} \longrightarrow$ (c) $\mathrm{CH}_{3} \mathrm{O}^{-} \mathrm{Na}^{+}+\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}-\mathrm{Br} \underset{\mathrm{CH}_{3} \mathrm{OH}}{\longrightarrow}$ (d) $\mathrm{EtO}^{-} \mathrm{K}^{+}+\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}_{2}-\mathrm{OTs} \underset{\mathrm{EtOH}}{\frac{25^{\circ} \mathrm{C}}{25}}$

Complete the following reactions. If no reaction is likely, explain why.
(a) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\mathrm{OH}+\mathrm{Na} \longrightarrow \stackrel{\mathrm{CH}_{3} \mathrm{I}}{\longrightarrow}$
(b) $\mathrm{CH}_{3} \mathrm{SH}+\mathrm{NaOH}_{(1 \text { equiv. })} \longrightarrow$
(c) $\mathrm{CH}_{3} \mathrm{O}^{-} \mathrm{Na}^{+}+\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}-\mathrm{Br} \underset{\mathrm{CH}_{3} \mathrm{OH}}{\longrightarrow}$
(d) $\mathrm{EtO}^{-} \mathrm{K}^{+}+\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}_{2}-\mathrm{OTs} \underset{\mathrm{EtOH}}{\frac{25^{\circ} \mathrm{C}}{25}}$

Key Concepts

Williamson Ether Synthesis

This synthesis method involves the reaction of an alkoxide ion with a primary alkyl halide to create an ether. It is an essential strategy for constructing ethers and relies on the availability of both a good nucleophile (the alkoxide) and a good electrophile (usually a primary or sometimes secondary alkyl halide) under conditions that minimize competing elimination reactions.

Formation of Alkoxides and Thiolates

Deprotonation of alcohols and thiols by a strong base generates alkoxides and thiolates, respectively. These anions are important nucleophiles in organic synthesis, typically used in substitution reactions like the Williamson Ether Synthesis. The acidity of the starting molecule determines how readily the nucleophile is formed and, subsequently, how effective it is in attacking an electrophilic center.

Steric Hindrance Effects in Reaction Mechanisms

Steric hindrance refers to the inhibition of chemical reactions due to the spatial crowding around reactive centers. In substitution reactions, bulky substituents around the electrophilic carbon can impede the approach of the nucleophile, favoring mechanisms that do not require a backside attack (such as SN1) or even leading to no reaction in the case of severely hindered substrates like neopentyl systems. Recognizing steric effects is vital when predicting whether a substrate will undergo substitution or elimination.

Nucleophilic Substitution (SN1 and SN2)

This concept involves the replacement of a leaving group in a molecule by a nucleophile through two primary pathways: SN1, which goes through a carbocation intermediate and is favored by tertiary substrates and polar protic solvents, and SN2, a concerted mechanism favored by primary substrates, strong nucleophiles, and minimal steric hindrance. Understanding which pathway dominates helps predict the product outcome in reactions involving alkyl halides and nucleophiles.

Elimination Reactions (E2)

E2 elimination reactions occur when a strong base removes a proton adjacent to a leaving group, leading to the formation of a double bond. These reactions are highly dependent on factors such as the strength of the base, substrate structure (especially the degree of substitution), and the reaction conditions. Recognizing when elimination is favored over substitution is crucial for predicting the formation of alkenes in organic reactions.

Leaving Group Ability

The effectiveness of a leaving group is fundamental to both substitution and elimination reactions. A good leaving group can stabilize the negative charge after dissociation, thereby facilitating the reaction process. Common leaving groups, such as halides and sulfonate esters, have different intrinsic abilities to depart from the substrate, influencing the overall reaction rate and mechanism.

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