Final answer:
The halide attaches to the sp² carbon with the most hydrogens in halohydrin formation due to regioselectivity and the stability of the more substituted carbocation intermediate formed during the reaction.
Step-by-step explanation:
In halohydrin formation, the halide ends up attached to the sp² carbon bonded to the most hydrogens due to regioselectivity influenced by the mechanism of electrophilic addition. This regioselectivity is often explained by Markovnikov's rule, which states that in the addition of a protic acid HX to an alkene, the acid hydrogen (H) becomes attached to the carbon with the greatest number of hydrogen atoms, and the halide (X) bonds to the carbon with more alkyl substituents.
The underlying reason for this preference lies in the formation of the more stable carbocation intermediate during the reaction. The carbon that is bonded to more hydrogen atoms tends to be less sterically hindered and more accessible to the attacking electrophile, and if a carbocation is formed, the one with more alkyl substituents (which are electron-releasing through hyperconjugation) is more stable. However, the stereochemistry of this addition can be influenced by various factors, including the nature of the solvent, the presence of a catalyst, the specific alkene, and the identity of the acid halide, which can lead to exceptions from the Markovnikov's rule.