Borazines undergo nucleophilic attack at boron and electrophilic attack at nitrogen. The nucleophilic phosphine attacks the azide at the electrophilic terminal nitrogen. Thus, ketones are nucleophilic at oxygen and electrophilic at carbon. Alkylating agents are often classified according to their nucleophilic or electrophilic character. An alternative to aromatic substitution is electrophilic aliphatic substitution. These procedures require fairly electrophilic and nucleophilic radicals, respectively, to proceed effectively. Carbenes can be classified as nucleophilic, electrophilic, or ambiphilic. It undergoes many reactions including Diels-Alder additions to electrophilic alkenes and alkynes. These dipoles add to electrophilic alkenes readily. Toluene reacts as a normal aromatic hydrocarbon in electrophilic aromatic substitution. They are nucleophiles that add to a variety of electrophilic and unsaturated substrates. In electrophilic aromatic substitution reactions, naphthalene reacts more readily than benzene. Like phenols, aniline derivatives are highly susceptible to electrophilic substitution reactions. Quinones are electrophilic Michael acceptors stabilised by conjugation. Cycloaliphatic epoxides are therefore usually homopolymerized thermally or UV-initiated in an electrophilic or cationic reaction.