Chemistry · Haloalkanes And Haloarenes · NEET
Follow four steps. (1) Find the longest carbon chain and name it as the alkane (e.g. hexane). (2) Treat the halogen as a substituent with the prefix fluoro, chloro, bromo, or iodo. (3) Number the chain from the end that gives the substituents the lowest set of locants. (4) Write the halogen prefixes and any other prefixes in alphabetical order before the parent name. Example: CH3-CHCl-CH3 is 2-chloropropane. This is a guaranteed NEET direct-name question, so the steps must be automatic.
The -OH group wins. Halogens (fluoro, chloro, bromo, iodo) are ALWAYS just prefixes; they never become the main functional group. So -OH (-ol) is the principal characteristic group and is written as a suffix, and the chain is numbered to give -OH the lowest locant. This is exactly why the NEET 2022 answer is 1-bromo-5-chloro-4-methylhexan-3-ol and not a name where a halogen got the low number.
Halogens are always substituents (prefixes), never the suffix. That is the single most important rule for this topic. When only halogens are present, you name the compound as a halo-substituted alkane. When -OH, -COOH, -CHO, C=O, or -NH2 is also present, that group becomes the suffix and the halogen stays a prefix. Weak students lose easy marks by treating a halogen like the main group.
For haloarenes the benzene ring is the parent. C6H5Cl is chlorobenzene. When two halogens are on the ring you use locants 1,2 (ortho), 1,3 (meta), or 1,4 (para): so 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene. The common names o-, m-, and p-dichlorobenzene mean the same thing. Number to give the lowest set of locants.
Because -OH is the principal group and must get the lowest possible number. Numbering from the bromo end puts -OH at C3; numbering from the other end would put -OH at C4. Since 3 is lower than 4, we number from the Br end. That fixes Br at C1, methyl at C4, Cl at C5, giving 1-bromo-5-chloro-4-methylhexan-3-ol. The wrong option numbers from the wrong end and repeats groups incorrectly.
Alphabetical by the first letter of the substituent name: bromo (b), chloro (c), fluoro (f), iodo (i), methyl (m). So in a name you write bromo before chloro before methyl. Multiplying prefixes like di, tri, tetra are IGNORED when alphabetizing (dibromo alphabetizes under 'b'). This ordering rule is a common NEET trap: the LOWEST locant is decided by the chain, but the WRITING order is alphabetical.
Use the 'first point of difference' rule. Compare the full set of locants from both ends; choose the direction that gives the lower number at the first point where they differ. If locant sets are identical, then give the lowest locant to the substituent that comes first alphabetically. This tie-breaker appears in tricky NEET naming questions.
The correct IUPAC name of the compound with a six-carbon chain bearing Br at C1, OH at C3, a CH3 branch at C4, and Cl at C5 is:
The compound C6H5-CH=CH-CH(Br)-CH2-CH3 (a benzene ring, then -CH=CH-, then an sp3 carbon carrying Br next to the C=C) is an example of a:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
No. Halogens are always prefixes (fluoro, chloro, bromo, iodo). If a group like -OH, -CHO, -COOH, C=O or -NH2 is present, that becomes the suffix and the halogen stays a prefix.
Common names name them as alkyl halides, e.g. CH3Cl is methyl chloride, CH3CH2Br is ethyl bromide, (CH3)3CCl is tert-butyl chloride. NCERT lists both, but IUPAC names are safer for NEET.
Both halogens are prefixes with locants: e.g. CH2Cl-CH2Cl is 1,2-dichloroethane (a vic-dihalide), and CH3-CHCl2 is 1,1-dichloroethane (a gem-dihalide). In common names these are ethylene dichloride and ethylidene chloride.
As a haloarene. The benzene ring is the parent, so C6H5Cl is simply chlorobenzene. The halogen sits directly on an sp2 aromatic carbon, which makes it an aryl halide.
NEET almost every year has a direct 'give the IUPAC name' or 'classify the halide' question, like NEET 2022 and 2023. These are easy, fast marks if your naming rules are automatic, so this is one of the highest return-per-minute topics.
