Chemistry · Haloalkanes And Haloarenes · NEET
Both sit near a C=C double bond, but the carbon holding the halogen is different. In an ALLYLIC halide the halogen is on an sp3 carbon that is NEXT TO the C=C (one bond away). Example: CH2=CH-CH2-Cl. In a VINYLIC halide the halogen is directly ON the sp2 carbon of the C=C itself. Example: CH2=CH-Cl. Simple test: is the C-X carbon part of the double bond (vinylic, sp2) or just beside it (allylic, sp3)? This exact idea was tested in NEET 2023.
No. Benzyl chloride is a BENZYLIC halide, not an aryl halide. The halogen is on the CH2 group (an sp3 carbon) that hangs off the ring, not on the ring carbon itself. An ARYL halide (like chlorobenzene) has the halogen directly bonded to an sp2 ring carbon. Rule: halogen on the ring carbon = aryl (sp2); halogen on a carbon attached to the ring = benzylic (sp3).
Both are dihaloalkanes (two halogen atoms). In a GEMINAL (gem) dihalide both halogens are on the SAME carbon, like CH3-CHCl2 (ethylidene chloride). In a VICINAL (vic) dihalide the two halogens are on ADJACENT carbons, like CH2Cl-CH2Cl (ethylene dichloride). Memory hook: gem = 'together on one', vic = 'neighbours'. In common names gem = alkylidene halide, vic = alkylene dihalide.
Because the halogen is joined to an sp2-hybridised carbon of the aromatic ring, not to an sp3 carbon of a chain. In an alkyl halide (haloalkane) the C-X carbon is sp3. Since the ring carbon is sp2, chlorobenzene belongs to the haloarene family. This sp3-vs-sp2 difference is the whole reason haloarenes react very differently from haloalkanes.
It just counts the halogen atoms. MONO = one halogen (CH3Cl, methyl chloride). DI = two halogens (CH2Cl2). POLY = three or more (CHCl3 chloroform, CCl4). This first split is by NUMBER only; after that you further classify by the type of carbon (sp3/sp2) and its position (alkyl, allylic, benzylic, etc.).
Follow two steps. Step 1: look at the carbon bonded to X. Is it sp3 or sp2? Step 2: check its neighbours. If sp3 and just a normal chain = alkyl. If sp3 and next to C=C = allylic. If sp3 and next to a benzene ring = benzylic. If sp2 and part of C=C = vinylic. If sp2 and part of a benzene ring = aryl. Do sp3/sp2 FIRST; it removes half the wrong options instantly.
The compound C6H5-CH=CH-CH(Br)-CH2-CH3 (a benzene ring with a -CH=CH- unit, then an sp3 carbon bearing Br adjacent to the C=C) is an example of a:
Which of the following can be used as the halide component for a Friedel-Crafts (alkylation) reaction?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is a dihalide because it has two chlorine atoms. Since the two chlorines are on the same single carbon, it is also technically a gem-type arrangement (only one carbon exists here).
Both are sp3. In each, the halogen sits on an sp3 carbon that is beside a double bond (allylic) or beside a benzene ring (benzylic). Only vinylic and aryl halides have the halogen on an sp2 carbon.
Yes, and this is why NEET tests it. sp3 C-X compounds (alkyl, allylic, benzylic) undergo substitution and elimination easily. sp2 C-X compounds (vinylic, aryl) have a stronger, shorter C-X bond and are far less reactive toward these reactions.
Gem-dihalide has both halogens on the SAME carbon; vic-dihalide has them on ADJACENT (neighbouring) carbons.
Yes for the common NEET case: haloarenes are aromatic compounds with halogen on the ring, i.e. aryl halides. Both mean an sp2 (ring) carbon bonded to a halogen.
