Question

Explain, why (a) Vinyl chloride is less reactive than ethyl chloride. (b) Allyl chloride is more reactive than vinyl chloride.

Short answer

Vinyl chloride is less reactive due to the stronger sp2 C-Cl bond. Allyl chloride is more reactive than vinyl chloride because of resonance stabilization.

Step-by-step solution

Understand the Reactants

Vinyl chloride is a compound with the formula C2H3Cl, where the chlorine atom is attached to an sp2 hybridized carbon in the vinyl group. Ethyl chloride is C2H5Cl, where the chlorine is bonded to an sp3 hybridized carbon.

Evaluate Bond Strength and Reactivity

Vinyl chloride's C-Cl bond involves an sp2 hybridized carbon, which has a stronger bond (due to partial double-bond character and resonance stabilization) than the sp3 carbon C-Cl bond in ethyl chloride. Stronger bonds in vinyl chloride make it less reactive than ethyl chloride.

Examine Stability Factors for Allyl Chloride and Vinyl Chloride

Allyl chloride (C3H5Cl) involves a chlorinated compound where the chlorine atom is connected to an sp3 hybrid carbon adjacent to a carbon-carbon double bond (pi bond). This arrangement allows potential resonance stabilization, making it more reactive than vinyl chloride.

Assess the Role of Resonance in Reactivity

Allyl chloride benefits from resonance structures, allowing electron delocalization which stabilizes the transition state during reactions. Vinyl chloride lacks such resonance stabilization, increasing its bond's stability and reducing reactivity.

Key concepts

Vinyl Chloride

Vinyl chloride, with the chemical formula C\(_2\)H\(_3\)Cl, is an organochlorine compound where the chlorine atom is bonded to an sp\(^2\) hybridized carbon atom. This specific hybridization is characteristic of the vinyl group, which contributes to the unique properties of the compound. The sp\(^2\) hybridized carbon gives the chlorine-carbon bond (C-Cl) in vinyl chloride a partial double-bond character.
This partial double-bond character occurs due to the pi-electron cloud in the double bond, which somewhat restricts chlorine's ability to act as a leaving group in chemical reactions. This makes vinyl chloride inherently less reactive compared to similar compounds where the chlorine is connected via a single bond to an sp\(^3\) hybridized carbon.
Applications of vinyl chloride include its use as a monomer in the production of polyvinyl chloride (PVC), a plastic widely used in various industries.

Ethyl Chloride

Ethyl chloride is another important organochlorine compound with the formula C\(_2\)H\(_5\)Cl. Unlike vinyl chloride, the chlorine atom in ethyl chloride is bonded to an sp\(^3\) hybridized carbon, which is part of an ethyl group. This bonding type results in a weaker carbon-chlorine bond compared to the bond in vinyl chloride because it lacks the additional pi-bonding interaction found in vinyl groups.
Here are some key points:

• The C-Cl bond in ethyl chloride is a pure single bond.
• This bond has increased length and is easier to break during reactions.

The decreased bond strength leads to higher reactivity, making ethyl chloride much more prone to participating in nucleophilic substitution reactions. Ethyl chloride is used in various applications, including as a solvent and in the preparation of ethyl cellosolve.

Allyl Chloride

Allyl chloride, with the chemical formula C\(_3\)H\(_5\)Cl, is characterized by a chlorine atom connected to an sp\(^3\) hybridized carbon that is adjacent to a carbon-carbon double bond. This distinctive setup allows allyl chloride to enjoy resonance stabilization, a phenomenon absent in vinyl chloride.
Resonance stabilization enables the electrons to delocalize, reducing the overall energy of the compound and facilitating increased reactivity in chemical processes. It transforms what would be a simple single bond into a dynamically stabilizing resonance hybrid.
Due to this resonance, allyl chloride is particularly reactive in substitution reactions as it can transition through an intermediate state that spreads out positive charges across multiple atoms.

Bond Strength

Bond strength is a crucial factor influencing the reactivity of chemical compounds, including various organic chlorides. The measure of bond strength typically involves evaluating the bond energy, which is the amount of energy required to break a bond apart. In organic chemistry, bonds associated with sp\(^2\) hybridized carbons, like in vinyl chloride, tend to be stronger due to additional bonding interactions.
The difference between sp\(^2\) and sp\(^3\) hybridized carbon bonding essentially lies in the overlap of orbitals:

• sp\(^2\) hybridized carbon results in more effective p-orbital overlap, creating stronger bonds.
• sp\(^3\) carbon forms bonds that are longer and inherently weaker.

As a result, compounds like vinyl chloride with stronger C-Cl bonds exhibit decreased chemical reactivity, while those like ethyl chloride with weaker bonds show increased reactivity.

Resonance Stabilization

Resonance stabilization is an important concept in organic chemistry that affects molecular stability and hence the reactivity of various compounds. It refers to the ability of electrons to distribute or delocalize over multiple atoms within a molecule, reducing the potential energy and usually increasing stability.
This concept is particularly relevant in allyl chloride, which possesses resonance forms that allow for the delocalization of electrons through the pi system of the double bond and a nearby single bond.
These resonance structures contribute to:

• A lower energy transition state during chemical reactions.
• Increased opportunity for chemical reactivity due to stabilization of intermediate forms.

In contrast, vinyl chloride lacks equivalent resonance forms because it does not have a similar arrangement of bonds, leading to different reactivity profiles compared to allyl chloride.