This lecture covers the reactions of olefins with electrophiles, the mechanism of electrophilic substitutions, regioselectivity in electrophilic additions, and the stereoselectivity of electrophilic additions. It explains how double bonds react with electrophiles to form carbocations, the regioselectivity of adding HX to olefins, and the competition of nucleophiles in reactions. Additionally, it discusses the addition of hydrogen halides, halogen addition, hydration, halohydrin formation, and the backside attack of nucleophiles enforcing trans addition.