BIOL 3305 Lecture Notes - Lecture 16: Ethylbenzene, Methoxy Group, Electrophilic Aromatic Directing Groups
Document Summary
Therefore meta substitution of toluene does not show any (significant) enhancement of rate relative to benzene. The methyl group is slightly electron donating (not by resonance or conjugation but by another effect we shall see later), and so stabilizes the intermediate sigma complex, and therefore the ts leading to it. This effect is pronounced in ortho and para attack since these give rise to resonance structures which contain tertiary carbons, and are therefore more stable. Meta substitution does not show these huge stabilizations, and is only slightly more stable then the unsubstituted benzene case: substitution with other activating ortho/para directing substituents. The results found with toluene are general for any alkyl substituted benzene undergoing eas. Any alkyl benzene will under eas faster than benzene itself, and will generate products that are primarily ortho and para. The alkyl group is an activating group, and is ortho and para directing.
