Help with Substitution Reactions

Cyanide is a weak base and a good nucleophile, and the solvent is aprotic; therefore, the product is favored. This involves 100% inversion of stereochemistry; therefore II is favored.

A substitution reaction is a chemical reaction that occurs when the reactants exchange atoms to form new products. In the reaction given the chloride in chloromethane is substituted for the hydroxide in sodium hydroxide to form methanol. Also the hydroxide in sodium hydroxide is substituted for the chloride in chloromethane to form sodium chloride.

SN1 reactions occur in two steps. First, the leaving group leaves, forming a carbocation. Next, the weak nucleophile attacks the carbocation (beware of rearrangements during this step). The protic solvent stabilizes the carbocation intermediate.

SN2 reactions undergo substitution via a concerted mechanism. Thus, no carbocation is formed, and an aprotic solvent is favored. Furthermore, tertiary substituted substrates have lowest reactivity for SN2 reaction mechanisms due to steric hindrance.

An reaction is most efficiently carried out in a protic solvent. An inverted configuration site is characteristic of an reaction and the substituted nucleophile does not form a pi bond in an reaction.

All of the given answers reflect SN1 reactions, except the claim that SN1 reactions are favored by weak nucleophiles.

SN1 reactions occur in two steps and involve a carbocation intermediate. The product demonstrates inverted stereochemistry (no racemic mixture). Tertiary substrates are preferred in this mechanism because they provide stabilization of the carbocation.

A solvolysis reaction is simply an reaction where the solvent acts as a nucleophile.

In this case, we start with a tertiary alkyl halide. Bromine, a stellar leaving group, leaves the substrate and leaves a carbocation intermediate. The methanol is then free to attack the carbon chain at the site of the carbocation to form an ether. The correct answer is 2-methoxy-2-methylpropane.

SN2 reaction mechanisms are favored by methyl/primary substrates because of reduced steric hindrance. No carbocation is formed via an SN2 mechanism since the mechanism is concerted; thus a strong nuclephile is used.

Substitution reactions—regardless of the mechanism—involve breaking one sigma bond, and forming another sigma bond (to another group).

The reaction shown is a nucleophilic substitution reaction. The molecule shown is a primary alkyl bromide, and the nucleophile that will be used is the iodide anion (). In this type of reaction the iodide will displace the bromide on the organic molecule, generating iodoethane ().