Final answer:
The addition of molecular halogens to alkenes in a non-nucleophilic solvent is characterized by the electrophilic addition mechanism, producing vicinal dihalides. It involves the initial formation of a halonium ion intermediate and is influenced by regioselectivity and stereoselectivity. The process includes electron movement depicted with curly arrows.
Step-by-step explanation:
The mechanism of molecular halogen addition to alkenes in a non-nucleophilic solvent involves the electrophilic addition of the halogen. This reaction is regioselective, stereoselective, and can be stereospecific. In the first step, the alkene forms a weak bond with the halogen molecule due to the polarizable electrons of the double bond, creating a halonium ion intermediate. Then, the second halogen atom attacks the more substituted carbon of the halonium ion, leading to the vicinal dihalide product.
For alkenes, these additions are typically anti-additions due to the formation of a cyclic halonium ion intermediate. Curly arrows are used to indicate the movement of electrons during the mechanism.
Regioselectivity refers to the preference of one direction of chemical bond making or breaking over other possible directions. Stereoselective reactions produce one stereoisomer preferentially, while stereospecific reactions yield stereoisomeric products in a predictable manner based on the reactant stereoisometry. Tautomerism may also occur after certain electrophilic additions, leading to different constitutional isomers.