This is an example of a Grignard reaction that requires the use of an ester or acid chloride, and more than one equivalent of an organometallic. The second step would be to react the product of the first step in an acidic source.

In the HVZ reaction of a carboxylic acid, a bromine is added to the alpha carbon. Phosphorus catalyzes the reaction and allows for the formation of an acyl halide. Acyl halides readily undergo enol-ketone tautomerization. The enol form uses electrons from the carbon-carbon double bond to bond to the bromine. In water, the two bromine molecules convert back to a carboxylic acid with one bromine on the alpha carbon.

This question tests knowledge on carboxylic acid derivatives and the formation of the carboxylic acid derivatives. , or thionyl chloride, reacts with a carboxylic acid to form an acid chloride. The choice that replaces the  with a . The reaction also expels .

5-hydroxyvaleric acid (5-hydroxypentanoic acid) is a five-carbon carboxylic acid alcohol and will produce the required lactone. This reaction is typically acid-catalyzed. Pentanedioic acid (glutaric acid) is a linear dicarboxylic acid, 4-hydroxybutyric acid only has four carbons and will not produce the desired product without being modified.

The  group replaces the halogen as the halogen is a better leaving group. Lithium aluminum hydride is a strong reducing agent. It takes nitrogen-nitrogen bonds and allows for nitrogen hydrogen bonds to be formed instead. A primary nitrogen is bonded to two hydrogens and one R group. After reduction, a primary amine is formed.

The reaction given is for the nucleophilic addition of a secondary amine to a ketone. Below is the mechanism for this acid catalyzed reaction:

The protonation of the hydroxyl group makes it a better leaving group.

This is a Diels-Alder reaction; these reactions happen between a nucleophilic diene, shown in blue below, and an electrophilic dienophile, in green. Diels-Alder reactions install a set of bonds that connect each external carbon of the diene system to an alkene carbon in the dienophile system to create a new six-membered ring. All remaining structure of the two reactants are retained, including the six- and five-membered rings below. The red bonds are the newly installed bonds.

The electrons from one of the double bonds on the 1,3-dibutene create a new single bond. The other new single bond is created from the electrons in the double bond of the other reactant. These two new single bonds join the reactants to create a cyclic product.

The electrons from the other double bond in the 1,3-dibutene move between the carbon 2 and 3. Thus, the final product is a 6-carbon cycloalkene with a halogen substituent.

This is a standard Diels-Alder reaction. Diels-Alder reactions are driven solely by adding heat to the reagents. By looking at the reagents and the product, we can tell that this is a Diels-Alder reaction. For Diels-Alder, we need a cis-diene and an alkene as reactants. When these reactants are stimulated by heat, they form a cyclohexene product.

This is a classic Diels-Alder reaction and it consists of a diene (cyclopentadiene) and a dienophile (ethene). The bicyclic structure forms if the electrons are moved in a circular fashion.