Chapter 16: Electrophilic Attack on Derivatives of Benzene (Substituents Control Regioselectivity) Flashcards
Activators
electron donors
direct ortho/para
Deactivators
electron acceptors
direct meta
cause further electrophilic aromatic substitution and incorporation of donors (Friedel-Crafts alkylation) causes substitution to accelerate
Induction
occurs in σ bonds
tapers off rapidly with distance
governed by relative electronegativity of atoms and polarization of bonds
Resonance
takes place in π bonds
has a longer range and is strong in charged systems
-CH3
inductive donors
activator
ortho/para
Alkyl Groups
inductive donors
activator
ortho/para
-CF3
electron withdrawing due to electronegative F
deactivator
meta
Heteroatoms (N, O, Halogens)
inductive withdrawing due to electronegativity and + charged atoms (carbonyl, cyano, nitro, and sulfonyl)
deactivators
meta
Inductive Donors
activating
ortho/para
intermediate carbocation is next to an electron donating group, stabilizes it
ortho/para products are formed in different amounts due to steric effects
Inductive Acceptors
deactivating
meta
inductive e-withdrawing substituents destabilize carbocation at all positions, ortho/para put + charge next to e- accepting group, less favored than meta
Resonance Donors
activating
ortho/para
Resonance Acceptors
deactivating at all positions, lesser extent at meta
meta
avoids + charge next to e-withdrawing groups
Halogens
deactivating
ortho/para
withdraw inductively, donate by resonance
Disubstituted Benzene Substitution Rules
- most powerful activator controls position of attack
- power of substitutes is ranked into three groups
I. NR2, OR > II. X, R > III. meta directors - discount ortho attack to bulky groups or between two substituents
- rules 1-3 are applicable to more highly substituted benzenes
