Halogenation Reactions - Online Tutor, Practice Problems & Exam Prep

Halogenation reactions involve the addition of halogens like bromine (Br₂) or chlorine (Cl₂) to alkenes, where each carbon in the double bond (pi bond) gains a halogen atom. When a single pi bond is present, the reaction yields a dihalide, with two halogens added to the alkene. For alkynes, which contain two pi bonds, two moles of the halogen reagent are required, resulting in a tetrahalide with four halogen atoms added. This process is crucial for transforming unsaturated hydrocarbons into more reactive halogenated compounds, expanding the utility of these organic molecules in chemical synthesis.

Halogenation Reactions

In this reaction, we're going to talk about the halogenation reactions here. Under this type of reaction, 2 halogens coming from either BR₂ or CL₂ are added to one Pi bond. So here we have our starting alkene and we're reacting it with X₂. In the process, each double bonded carbon gains 1 halogen. At the end of this we have a structure that has two halogens on it, which we call a dye halid.

Now if we have an alkyne, that means we have 2 π bonds. So remember we need one mole of reagent for every π bond, and since there's 2 π bonds here, we'd need 2 moles of X₂. So the first mole would add to give us two halogens, and then the second mole would add again to give us another two halogens. At the end, you have a structure that possesses 4 halogens on it, so we'd call this a tetrahalid.

So remember, halogenation. Halogenation is just adding two halogens per π bond within your structure. This could give us a dye halid if you're dealing with an alkene, or a tetrahalid if you're dealing with an alkyne.

Halogenation Reactions Example

Complete the following halogenation reaction. So here we have our alkene and we're reacting it with one mole of chlorine. Remember, all that's going to happen here is we're going to sacrifice our π bond in order to add 2 halogens to my structure.

Each double bonded carbon gets a chlorine here. It doesn't matter the orientation that you place the chlorine, if it's up or down or whatever, all that matters is the connection. It's these two double bonded carbons that each need to have their chlorines.

Here I decide to show them as being on opposite sides of each other, but I could show them being on the same side. We don't go into spatial orientation when it comes to a reaction like this. That's left for when we do organic one and organic 2. For right now, this would be our dihalid structure completed from the following halogenation reaction.

Write a halogenation reaction of the following alkyne with Br₂ and name the product formed.

• A.
• B.
• C.
• D.

Here’s what students ask on this topic:

Which statement describes the products expected from the halogenation reaction shown below?

To provide an accurate response, I would need the specific halogenation reaction you're referring to. Halogenation reactions typically involve the addition of halogen atoms (such as fluorine, chlorine, bromine, or iodine) to another substance. In organic chemistry, halogenation can occur in alkanes, alkenes, and alkynes, among other compounds.

For example, if you have an alkene undergoing halogenation with bromine (Br₂), the product would be a vicinal dibromide, where each of the carbon atoms that were previously involved in the double bond now has a bromine atom attached to it.

If you're looking at the halogenation of an alkane with chlorine (Cl₂) under UV light, the reaction typically replaces one of the hydrogen atoms with a chlorine atom, resulting in a chloroalkane and hydrochloric acid as a byproduct.

Please provide the specific reaction for a more detailed description of the products you can expect from the halogenation process you are studying.

What is a halogenation reaction?

A halogenation reaction is a type of chemical reaction where a halogen (fluorine, chlorine, bromine, iodine, or astatine) is introduced into a molecule, typically replacing one or more hydrogen atoms. This process forms a new compound known as a halogenated compound. Halogenation can occur in various substrates, including alkanes, alkenes, and aromatic compounds, and the reaction can be initiated by heat, light, or the presence of a catalyst.

For example, in an alkane, a halogenation reaction can proceed through a radical chain mechanism, where the halogen molecule dissociates to form radicals that can abstract hydrogen atoms from the alkane, leading to the formation of alkyl halides. In alkenes, halogenation adds halogens across the double bond, resulting in vicinal dihalides. In aromatic halogenation, the reaction typically occurs via an electrophilic aromatic substitution mechanism, where the halogen, often in the presence of a Lewis acid catalyst, substitutes for a hydrogen atom on the aromatic ring.

Is halogenation of an alkene a(n) _____ reaction, where the halogens add in a(n) _____ fashion?

Halogenation of an alkene is an addition reaction, where the halogens add in an anti fashion. During this process, the π bond of the alkene breaks, and each carbon atom of the former double bond attaches to a halogen atom. The term 'anti addition' refers to the fact that the two halogen atoms add to opposite sides of the plane of the alkene, leading to the formation of a vicinal dihalide. This occurs because the initial step of the reaction involves the formation of a halonium ion intermediate, which is a three-membered ring structure where the halogen is positively charged. The second halogen atom then attacks from the side opposite to this intermediate, resulting in the anti addition pattern.

Which of the following is an example of a halogenation reaction?

A halogenation reaction is a type of chemical reaction where a halogen (fluorine, chlorine, bromine, iodine, or astatine) is incorporated into a compound, typically by substitution or addition. An example of a halogenation reaction is the chlorination of methane, where a chlorine molecule reacts with methane to produce chloromethane and hydrochloric acid:

${\mathrm{CH}}_4+{\mathrm{Cl}}_2\to {\mathrm{CH}}_3\mathrm{Cl}+\mathrm{HCl}$

In this reaction, one of the hydrogen atoms in the methane molecule is replaced by a chlorine atom, which is a classic example of a substitution halogenation. This type of reaction is often facilitated by light or heat, which helps to break the diatomic halogen molecule into reactive halogen atoms.