CBSE Ncert Notes for Class 12 Chemistry Haloalkanes and Haloarenes. Halo alkanes are the compounds containing halogen atom attached to the sp3. Haloalkanes are the organic compound formed by replacing a hydrogen atom by a halogen atom. They have general structure formula R-X, where R is an alkyl. CBSE class 12 Haloalkanes and Haloarenes class 12 Notes Chemistry in PDF are available for free download in myCBSEguide mobie app.
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Chapter 10 – The Haloalkanes and Haloarenes, to give you a quick glance of the chapter. The main topics covered in this part are: In aliphatic or aromatic compounds, the replacement of hydrogen atom s by halogen atom s results in the formation of alkyl halide haloalkane and aryl halide haloarenerespectively.
CBSE Class 12 Chemistry Notes Chapter 10 Haloalkanes and Haloarenes – Download PDF Here
In case of haloalkanes, halogen atom is attached to the sp3 hybridised carbon atom of an alkyl group whereas in haloarenes, halogen atom is attached to sp2 hybridised carbon atom of an aryl group. The d- and f- Block Elements. The halogen derivatives of hydrocarbons may be classified as fluoro, chloro, halkarenes or iodo compounds according to the type of halogen present. Depending upon the number of halogens present, the halogen derivatives can be classified as mono, di, tri or polyhalo compounds.
On the basis of the nature of the carbon to which halogen atom is attached, halogen derivatives are classified as 1 o haloadenes, 2 o3 oallylic, benzylic, vinylic and aryl derivatives. Halogen atom is attached to an sp 3 – hybridised carbon atom next to an aromatic ring. Halogen atom is bonded to the sp2-hybridised carbon atom of an aromatic ring. Here X represents a halogen atom, i.
Nature of C-X bond in haloalkanes. X is more electronegative than carbon. So, the C-X bond is polarized with C having a partial positive charge and X having a partial negative charge.
By free radical halogenation of alkanes: Chlorination or bromination of alkane usually gives a complete mixture of isomeric mono and poly halo alkanes. By electrophilic addition of HX to alkene: An alkene is converted to corresponding alkyl halide by reaction with hydrogen chloride, hydrogen bromide or hydrogen iodide.
The hydroxyl group of an alcohol is replaced by halogen on reaction with concentrated halogen acids, phosphorus halides or thionyl chloride to give the corresponding alkyl halide. Academic Session — By electrophilic substitution reactio n: This involves the direct halogenation of benzene ring in the presence of Lewis acid catalysts like iron or iron III haloalkwnes.
Aniline is treated with sodium nitrite to give a diazonium salt which is then treated with cuprous chloride or cuprous bromide to produce the corresponding aryl halide:.
This involves the conversion of aryl amines to aryl fluorides via diazotisation and subsequent thermal decomposition of the derived aromatic fluoborate to produce the corresponding aryl fluoride. Physical properties of Haloderivatives.
Physical properties haloaeenes haloderivatives are different than those of the simple hydrocarbons. These are described below:.
This is because the greater polarity as well hwloalkanes higher molecular mass as compared to the parent hydrocarbon causes the intermolecular forces of attraction dipole-dipole and van der Waals to be stronger in the halogen derivatives. The inflammability decreases with increasing halogen content. A nucleophile attacks the haloalkane which is having a partial positive charge on the carbon atom bonded to halogen. Halide ion separates following a substitution reaction.
Reactivity of Haloalkanes towards nucleophilic substitution: Mechanism of nucleophilic substitution reaction: The nucleophilic substitution reaction can proceed via S N 1 mechanism or S N 2mechanism. This type of nucleophilic substitution takes ahloalkanes in two steps, first step being the rate determining step involves the formation of carbonium ion.
Nottes type of nucleophilic substitution takes place in one step. Alkyl halides react with sodium to form an alkane with double number of carbon atom than that present in alkyl halide. This reaction is also known as Wurtz reaction.
Stereoisomerism is due to the different orientation of atoms or groups in space. There are two types of stereoisomerism:. It arises due to the presence of like groups on the same side of the plane cis or on the opposite side of the plane trans. It arises due to the hlaoalkanes of non-superimposable mirror images.
Conditions for optical isomerism to take place are:. The two non-superimposable mirror images are called enantiomers. Enantiomers are haloareenes two types: These rotate the plane polarised light in a clockwise direction.
These rotate the plane polarised light in an anticlockwise direction.
CBSE Class 12 Chemistry Notes : Haloalkanes and Haloarenes
A mixture containing two enantiomers in equal proportions is called racemic mixture. A recemic mixture is optically inactive as the effect of one isomer gets cancelled by another isomer. Aryl halides are almost unreactive towards nucleophilic substitution reaction. This is because of double character of C — X bond due to resonance. Therefore, it is difficult to remove X from C — X bond.
Effect of NO 2 group on the reactivity of aryl halide towards nucleophilic substitution reactions: Presence of an electron withdrawing group like NO 2 group increases the reactivity of aryl halides towards nucleophilic substitution reaction.
NO 2 group increases the reactivity more when present at o – and p – position due to the increased delocalization of negative charge involving NO 2 group. A verifcation code has been sent to your mobile number.
Haloalkanes and Haloarenes Part – I. Jagran Josh Oct 17, The d- and f- Block Elements Classification of Haloalkanes: Preparation of Haloalkanes Haloalkanes can be prepared by a number of methods: Academic Session — Preparation of haloarenes Haloarenes can be synthesised by any of the following reactions: Aniline is treated with sodium nitrite to give a diazonium salt which is then treated with cuprous chloride or cuprous bromide to produce the corresponding aryl halide: By Balz — Schiemann reaction: Treatment of diazonium salt with potassium iodide gives aryl iodide.
These are described below: Haloslkanes of Haloalkanes The reactions of haloalkanes may be divided into the three main categories: The reactivity order of haloalkanes towards S N 1reaction is: The reactivity of alkyl halide towards S N 2 reaction is: There are two types of stereoisomerism: Conditions for optical isomerism to take hloalkanes are: These rotate the plane polarised light in an anticlockwise direction Racemic mixture A mixture containing two enantiomers in equal proportions is called racemic mixture.
Racemisation The process of conversion of enantiomers into a racemic mixture is known as racemisation. Reactions of Haloarenes Nucleophilic substitution: Haloalkanes and Haloarenes Part – II.
Haloalkanes and Haloarenes class 12 Notes Chemistry
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