The reactions of primary and secondary alcohols with HCl require the presence of the catalyst ZnCl₂. The catalyst aids in the conversion of alcohols into alkyl halides in the presence of hydrochloric acid.

Thionyl chloride is preferred because it forms alkyl halides along with escapable gases SO₂ and HCl, ensuring the production of pure alkyl halides. The gaseous products can be easily removed.

In the common system, dihalogen derivatives use prefixes o-, m-, p-, while in the IUPAC system, numerals 1,2; 1,3; and 1,4 are used to denote the positions of halogen atoms in the benzene ring.

The configuration is inverted during the SN₂ reaction as the attacking nucleophile attaches to the carbon, resembling an umbrella turning inside out in a strong wind. This inversion of configuration occurs in the transition state as the reaction progresses.

In the SN₂ reaction, the incoming nucleophile interacts with the alkyl halide, causing simultaneous breaking of the carbon-halide bond and formation of a new bond between carbon and the attacking nucleophile. The transition state involves the inversion of configuration as ...