From refrigerants in air conditioners to medicines, Haloalkanes and Haloarenes are everywhere around us. These words are made up of two words: the first is ‘Halo’, which means Halogens, and the second word is ‘alkanes’ or ‘arenes’, which means aliphatic or aromatic hydrocarbons. These are organic compounds containing Halogens (Fluorine, Chlorine, Bromine, Iodine). These compounds play a crucial role in pharmaceuticals and industries. In these compounds, one or more Hydrogen atoms are replaced by Halogens. Many organic compounds containing halogens occur naturally and have clinical significance. Some of the widely used Haloalkanes are Chloroform (CHCl3) and Carbon tetrachloride (CCl4), and Haloarenes are DDT, Bromobenzene, etc.
Alkyl halides are organic compounds containing a halogen atom (F, Cl, Br, or I) bonded to an alkyl group. Alkyl halides are classified as primary, secondary, or tertiary based on the carbon atom attached to the halogen. Alkyl halides are versatile intermediates in organic synthesis, used in the production of polymers, refrigerants, and agrochemicals.
Haloalkanes exhibit unique physical properties like higher boiling points compared to alkanes due to the polar C-X bond and their larger molecular mass. Chemically, they undergo nucleophilic substitution (SN1 and SN2 mechanisms) and elimination reactions. The reactivity depends on the halogen and the carbon skeleton.
Haloarenes are aromatic compounds where one or more hydrogen atoms in an aromatic ring are replaced by halogen atoms. They are less reactive than haloalkanes due to resonance in the benzene ring, which delocalizes the electrons and stabilizes the C-X bond. Haloarenes find applications in pesticides, dyes, and pharmaceuticals.
Markovnikov's Rule predicts the outcome of electrophilic addition reactions to alkenes. It states that when a protic acid (HX) adds to an asymmetric alkene, the hydrogen atom attaches to the carbon with more hydrogen atoms, and the halide (or other substituent) attaches to the carbon with fewer hydrogen atoms. This rule is explained by the stability of the carbocation intermediate, which favors the more substituted and stable carbocation.
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(c) Benzylic halides: These are the halides in which the halogen atom is attached to sp3 hybridised carbon which is attached to an aromatic ring.
(d) Vinylic Halides: In this type of halide, the halogen atom is attached to sp2 carbon.
(e) Aryl Halides: In this type of halide, the halogen atom is sp2 carbon atom of an aromatic ring.
Preparation of Alkyl halides
There are some important applications of haloalkanes and haloarenes viz:
Question: Given below are two statements :
Statement (I) : SN2 reactions are 'stereospecific', indicating that they result in the formation only one stereo-isomers as the product.
Statement (II) : SN1 reactions generally result in formation of product as racemic mixtures. In the light of the above statements, choose the correct answer from the options given below :
(1) Statement I is true but Statement II is false
(2) Statement I is false but Statement II is true
(3) Both Statement I and Statement II is true
(4) Both Statement I and Statement II is false
Answer:
SN2→ Inversion
SN1→ Racemisation
Hence, the answer is the option (3).
Question: Given below are two statements :
Statement (I) : Alcohols are formed when alkyl chlorides are treated with aqueous potassium hydroxide by elimination reaction.
Statement (II) : In alcoholic potassium hydroxide, alkyl chlorides form alkenes by abstracting the hydrogen from the β-carbon.
In the light of the above statements, choose the most appropriate answer from the options given below :
(1) Both Statement I and Statement II are incorrect
(2) Statement I is incorrect but Statement II is correct
(3) Statement I is correct but Statement II is incorrect
(4) Both Statement I and Statement II are correct
Answer:
Statement (I) :
R−Cl→(aq,KOH)R−OH this reaction is nucleophilic substitution (SN2 or SN1), not elimination.
Statement (II) :
Hence, the correct answer is option (2).
Practice more questions from the link given below
For more questions to practice, the following MCQs will help in the preparation for competitive examinations
Alkyl Halides MCQ - Practice Questions with Answers. |
Physical & Chemical Properties of Haloalkanes MCQ - Practice Questions with Answers |
Haloarene MCQ - Practice Questions with Answers |
For this chapter, first, the NCERT book is best for initial level preparation as well as for board exams. Now, after this, if you want to prepare for competitive exams like JEE and NEET, then these are the best books for you: Morrison and Boyd, and R.K. Gupta by Arihant Publication. Meanwhile, in the preparation, you must continuously give mock tests for the depth of knowledge. Our platform will help you to provide a variety of questions for deeper knowledge with the help of videos, articles, and mock tests.
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Haloalkanes, also known as alkyl halides, are organic compounds that contain at least one halogen atom bonded to an alkane carbon atom. They can be classified into primary, secondary, and tertiary haloalkanes based on the degree of substitution of the carbon atom attached to the halogen.
Haloarenes are compounds where the halogen atom is attached to an aromatic ring, such as benzene. In contrast, haloalkanes have the halogen attached to a saturated carbon chain. This structural difference can lead to distinct physical and chemical properties, including reactivity and boiling points.
Haloalkanes are widely used in the chemical industry and household applications. They can serve as solvents, refrigerants, and intermediate compounds in the synthesis of pharmaceuticals, agrochemicals, and other organic compounds. Their ability to interact with various functional groups makes them versatile in chemical reactions.
Many haloalkanes are toxic and can contribute to environmental issues, especially when they are volatile or persist in the environment. Some members of this class, such as chlorofluorocarbons (CFCs), can deplete the ozone layer, while others may be harmful to aquatic life or human health if released into the environment.
When handling haloalkanes, it's important to work in a well-ventilated area or under a fume hood to avoid inhalation of fumes. Personal protective equipment, such as gloves and goggles, should also be worn to prevent skin and eye exposure, as many haloalkanes can be irritants or harmful.
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