Review Of Organic Chemistry Page 33
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34Organic Chemistry I Review: Highlights of Key Reactions, Mechanisms, and Principles
33
4 Classes of Substituents: Memorize! (Sections 17-6-8)
Donating? Memorize the list
Activating/Deactivating
Directing Effect
OH, OR, NH
, NHR, NR
Strong Activators
Ortho/para directors
2
2
R, Ar
Weak Activators
Ortho/para directors
Cl, Br
Weak Deactivators
Ortho/para directors
Carbonyl, NO
, CN, SO
H
Strong Deactivators
Meta directors
2
3
Note: Halogens are a special case that are ortho-para directors despite being deactivating
Otherwise, the following pattern is general:
Activator = ortho-para director (and vice versa,with exception of halides)
Meta director = deactivator (and vice versa,with exception of halides)
Rules for Additions to Disubstituted/Polysubstituted Aromatics (17.9)
1. Effects are additive if both direct to the same spot
2. If there is a conflict of interest, the more activating group controls the outcome
You need to know the relative activating/deactivating strengths!
3. Steric considerations: if two substituents have a 1,3 (meta) relationship, addition in between
(to give a 1,2,3 relationship) is prohibitively slow for steric reasons
Some Special “Combination” Sequences, to indirectly install NH
or CH
R groups, or to
2
2
install a new group ortho to an ortho-para director without competition from para-
insteallation.
2-Step Route to Add NH
:
2
1) HNO
, H
SO
(have NO
group, which is a meta director)
3
2
4
2
2) Fe, HCl (have NH
group, which is an ortho/para director)
2
at nitro stage, Nitrogen is a meta director
at amino stage, Nitrogen is an ortho-para director
2-Step Route to Add 1º Alkyl:
1) RCOCl, AlCl
(have COR group, which is a meta director)
3
2) Zn(Hg), HCl (have CH
R group, which is an ortho/para director)
2
at acyl stage, acyl carbon is a meta director
at alkyl stage, alkyl is an ortho-para director
Sulfonylation/Reaction/Desulfonylation:
1. SO
, H
SO
(protect, or block the para position)
3
2
4
2. Whatever (react, install at the ortho position)
3. H
O, H
SO
(deprotect, or unblock the para position)
2
2
4
Ideal procedure for when you have an ortho/para director, but you want an electrophile to
end up ortho rather than para
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