Question

Predict the reaction of propene with \(\mathrm{Br}_{2} / \mathrm{CC} \mathrm{I}_{4}, \mathrm{H}_{2} \mathrm{O} / \mathrm{H}_{2} \mathrm{SO}_{4}\) and HCI. Predict the reaction of toluene with these substances.

Short answer

Propene reacts with \(\mathrm{Br}_{2} / \mathrm{CC} \mathrm{I}_{4}\) to form 1,2-dibromopropane, with \(\mathrm{H}_{2} \mathrm{O} / \mathrm{H}_{2} \mathrm{SO}_{4}\) to form 2-propanol, and with HCl to form 2-chloropropane. Toluene reacts with \(\mathrm{Br}_{2} / \mathrm{CC} \mathrm{I}_{4}\) to form bromotoluene but doesn't react significantly with \(\mathrm{H}_{2} \mathrm{O} / \mathrm{H}_{2} \mathrm{SO}_{4}\) or HCl under normal conditions due to the stability of the benzene ring.

Step-by-step solution

Reaction of Propene with \(\mathrm{Br}_{2} / \mathrm{CC} \mathrm{I}_{4}\)

Propene, which is an alkene, undergoes a process known as halogenation when reacted with \(\mathrm{Br}_{2} / \mathrm{CC} \mathrm{I}_{4}\). This reaction leads to the addition of bromine across the double bond. The product of this reaction is 1,2-dibromopropane. Here is the reaction: \[ \text{Propene } + \text{ \(\mathrm{Br}_{2} / \mathrm{CC} \mathrm{I}_{4}\)} \rightarrow \text{ 1,2-dibromopropane} \]

Reaction of Propene with \(\mathrm{H}_{2} \mathrm{O} / \mathrm{H}_{2} \mathrm{SO}_{4}\)

When propene is reacted with \(\mathrm{H}_{2} \mathrm{O} / \mathrm{H}_{2} \mathrm{SO}_{4}\), it undergoes hydration. The water molecule adds across the double bond and forms an alcohol. According to Markovnikov's rule, the hydroxyl (OH) group will be connected to the carbon atom which has more hydrogen atoms. Therefore, the product of this reaction is 2-propanol. Here is the reaction: \[ \text{Propene } + \text{ \(\mathrm{H}_{2} \mathrm{O} / \mathrm{H}_{2} \mathrm{SO}_{4}\)} \rightarrow \text{ 2-propanol} \]

Reaction of Propene with HCl

The reaction of propene with HCl is an addition reaction. A molecule of HCl adds to the double bond of propene. According to Markovnikov's rule, the chloride ion will be attached to the carbon atom which has fewer hydrogen atoms. Hence, the product formed is 2-chloropropane. Here is the reaction: \[ \text{Propene } + \text{ HCl } \rightarrow \text{ 2-chloropropane} \] The reaction of toluene with these substances will differ from the above because toluene is an aromatic compound containing a methyl group (-CH3) attached to a benzene ring.

Reaction of Toluene with \(\mathrm{Br}_{2} / \mathrm{CC} \mathrm{I}_{4}\)

Toluene undergoes electrophilic aromatic substitution when reacted with \(\mathrm{Br}_{2} / \mathrm{CC} \mathrm{I}_{4}\). In the reaction, a bromine atom is added to the position where the CH3 group is attached to the benzene ring. The product of this reaction is bromotoluene. Here is the reaction: \[ \text{Toluene } + \text{ \(\mathrm{Br}_{2} / \mathrm{CC} \mathrm{I}_{4}\)} \rightarrow \text{ Bromotoluene} \]

Reaction of Toluene with \(\mathrm{H}_{2} \mathrm{O} / \mathrm{H}_{2} \mathrm{SO}_{4}\) and HCl

Toluene doesn't react significantly with \(\mathrm{H}_{2} \mathrm{O} / \mathrm{H}_{2} \mathrm{SO}_{4}\) or HCl under normal conditions, due to the delocalized pi system in the benzene ring, which gives it substantial stability and makes it less reactive than alkenes. High temperatures, pressures, or catalysts might be necessary to observe any significant reaction.

Key concepts

Alkene Reactions

Alkene reactions are fascinating and serve as a fundamental part of organic chemistry. Alkenes are hydrocarbons that contain at least one carbon-carbon double bond. This double bond makes them quite reactive. One of the most common reactions alkenes undergo is addition, where atoms or groups of atoms are added across this double bond.

For example, when propene (an alkene) reacts with \(\mathrm{Br}_{2} / \mathrm{CCl}_{4}\), bromine atoms add across the double bond to form 1,2-dibromopropane. This type of reaction is called halogenation. These reactions are not only interesting but also very useful in functionalizing hydrocarbons, turning simple alkenes into more complex structures with varied applications.

Markovnikov's Rule

Markovnikov's rule is an important guiding principle in organic chemistry, especially concerning reactions involving alkenes. This rule helps predict the addition pattern when alkenes react with reagents like HCl or \(\mathrm{H}_{2} \mathrm{O} / \mathrm{H}_{2} \mathrm{SO}_{4}\).

The rule states that in the addition of HX (where X is a halogen like Cl) to an alkene, the hydrogen atom (H) will attach to the carbon with more hydrogen atoms already present, while the halogen (X) attaches to the other carbon atom. For propene reacting with HCl, this results in 2-chloropropane because the chloride ion adds to the carbon with fewer hydrogen atoms. This rule helps predict the major product's structure in alkene addition reactions.

Aromatic Compounds

Aromatic compounds are characterized by their stable ring structure, primarily benzene rings, which have a distinct, delocalized pi electron cloud making them unique. Toluene is an aromatic compound where a methyl group is attached to a benzene ring. This structure provides stability and affects how it reacts with various substances.

In general, aromatic compounds do not undergo addition reactions like alkenes because that would disrupt their stable electron cloud. Instead, they often undergo substitution reactions, which allow the aromatic ring to retain its stability. These characteristics make aromatic compounds chemically distinct and integral to numerous industrial processes and products.

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a typical reaction mechanism for aromatic compounds, where an electrophile replaces a hydrogen atom in the aromatic ring. This mechanism is essential because it maintains the stability of the aromatic system.

When toluene encounters \(\mathrm{Br}_{2} / \mathrm{CCl}_{4}\), it undergoes EAS, where a bromine atom substitutes a hydrogen atom on the benzene ring, forming bromotoluene. The methyl group on toluene directs the bromination to occur at the ortho and para positions, as it is an activating group in these types of substitutions. This kind of reaction provides a valuable way to modify aromatic compounds while maintaining their core structure for further chemical synthesis.