BlogNCERTImportant Topic of Chemistry: Haloalkanes

Important Topic of Chemistry: Haloalkanes

Haloalkanes, commonly known as alkyl halides, are a class of chemical compounds in which one or more hydrogen atoms have been replaced by a halogen atom (fluorine, chlorine, bromine, or iodine).

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    The structural and physical properties of haloalkanes differ significantly from the structural and physical properties of alkanes. The structural variations are caused by the replacement of one or more hydrogen atoms with a halogen atom, as previously stated. Electronegativity, bond length, bond strength, and molecule size are all elements that influence physical qualities.

    Chemical properties of Haloalkanes

    Haloalkanes are a type of chemical molecule that is extremely reactive. The existence of a polar carbon–halogen link in their molecules contributes to their reactivity. Haloalkane reactions can be classified into the following categories.

    • Nucleophilic substitution reactions
    • Elimination reactions
    • Reaction with metals

    Nucleophilic substitution reactions: A nucleophilic substitution reaction occurs when an electron-rich nucleophile contacts a positively charged electrophile in order to replace a leaving group. The C6 carboxylate group is the most reactive nucleophile in carboxylate groups.

    The medium must be nonaqueous, which is a key condition for carrying out this reaction. Because water is a nucleophile, an aqueous solvent solution causes the reactive electrophile to react with water instead of alginate, which is undesirable. Furthermore, the electrophilic molecule may or may not be water-miscible. As a result, nucleophilic substitution processes can fully exploit the potential to dissolve alginates in organic mediums.

    Nucleophilic substitution reaction follows SN1& SN2 reaction mechanism, in which nucleophiles such as OH, CN, H2O, NH3 attack positively charged species.

    Elimination Reactions

    When a haloalkane containing a -hydrogen atom is heated with an alcoholic potassium hydroxide solution, the hydrogen atom from the -carbon atom is removed, and a halogen atom from the -carbon atom is formed.

    As a result, an alkene is generated as a result of the reaction. Elimination is often referred to as -elimination because the -hydrogen atoms are involved.

    Elimination Versus Substitution

    A chemical reaction is the outcome of competition; it is a race in which the quickest runner wins. A group of molecules will, for the most part, do what is easy for them. When an alkyl halide with -hydrogen atoms reacts with a base or a nucleophile, it takes one of two paths:

    Elimination and substitution (SN 1 and SN 2). The type of the alkyl halide, the strength and size of the base/nucleophile, and the reaction circumstances all influence which pathway is chosen. For steric reasons, a bulkier nucleophile will prefer to operate as a base and abstract a proton over approaching a tetravalent carbon atom, and vice versa.

    A primary alkyl halide prefers an SN 2 reaction, a secondary halide prefers an SN 2 or elimination reaction depending on the strength of the base/nucleophile, and a tertiary halide prefers an SN 1 or elimination reaction depending on the stability of the carbocation or the highly substituted alkene.

    Reaction with Metals

    The majority of organic chlorides, bromides, and iodides react with certain metals to form carbon-metal bonds. Organometallic compounds are the name for these types of chemicals. Alkyl magnesium halide, RMgX, often known as Grignard Reagents, is an important class of organometallic compounds discovered by Victor Grignard in 1900. The interaction of haloalkanes with magnesium metal in dry ether yields these reagents.

    FAQs – Frequently Asked Questions

    Are the halogenoalkanes dissolvable in water?

    In water, the halogenoalkanes are only very little soluble. In order for a halogenoalkane to dissolve in water, van der Waals dispersion and dipole-dipole interactions between halogenoalkane molecules must be broken, as well as hydrogen bonds between water molecules.

    Is it true that halogenoalkanes are flammable?

    Haloalkanes are less flammable than alkanes because they have fewer C–H bonds, and some are employed in fire extinguishers. Because of their higher polarity, haloalkanes are superior solvents to their alkane counterparts.

    When haloalkanes react with metals, what happens?

    Metals react with haloalkanes in a number of ways (zinc, magnesium and lithium). A metal atom is directly linked to a carbon atom in the compounds that result. Organometallic compounds are those in which the metal atom is directly linked to the carbon atom.

    Is it possible to reduce haloalkanes?

    Haloalkanes can be broken down into their constituent alkanes. Bromoethane can be converted to ethane, for example, by employing a metal catalyst such as nickel, palladium, or platinum, or by using hydroiodic acid (HI) in the presence of red phosphorus.

    What occurs when LiAlH4 is reacted with Haloalkane?

    Alkyl halides are reduced to alkanes using a variety of reducing agents such as lithium aluminium hydride (LiAlH4), H2 in the presence of a catalyst, and so on.

    Are haloalkanes saturated?

    Haloalkanes are saturated organic compounds in which the halogen atom is bonded to a single carbon atom, and all chemical linkages are single bonds.

    Is there a difference between alkanes and haloalkanes?

    Hydrocarbons having one or more hydrogen atoms substituted by halogen atoms are known as haloalkanes and haloarenes. Haloalkanes and haloarenes are distinguished by the fact that haloalkanes are formed from open-chain hydrocarbons (alkanes), whereas haloarenes are derived from aromatic hydrocarbons.

    What is the difference between haloalkanes and Haloarenes?

    Haloalkanes are chemicals created when hydrogen atoms in aliphatic hydrocarbons (alkanes) are replaced by halogen atoms. The compounds generated when hydrogen atoms linked to benzene rings are replaced by halogen atoms are known as haloarenes.

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