Q.What should be the correct IUPAC name of diethyl chloromethane? a) 3-Chloropentane b) 1-Chloropentane c) 1-Chloro-1,1-diethylmethane d) 1-Chloro-1-ethylpropane

Haloalkanes carry two naming systems side by side. The common system names the alkyl group first, then adds 'halide' -- methyl iodide, ethyl bromide, tert-butyl chloride, neo-pentyl bromide -- and is still widely used for simple, well-known compounds. The IUPAC system treats the halogen exactly like any other substituent: find the longest chain containing the halogen-bearing carbon, number it to give the lowest locant set overall, and cite the halogen as a fluoro-/chloro-/bromo-/iodo- prefix in alphabetical order alongside any other substituents, e.g. CH3-CH(Cl)-CH2-CH3 is 2-chlorobutane, and (CH3)3C-CH2-Br is 1-bromo-2,2-dimethylpropane (common name neopentyl bromide). Two refinements matter for exam questions: (1) when the halogen sits on an unsaturated chain, the double/triple bond gets priority for the lowest locant over the halogen, e.g. CH2=C(CH3)-CH2-Cl is numbered from the alkene end to give 3-chloro-2-methylprop-1-ene, not the other way round; (2) for a polyhalogenated ring or chain, every halo …