![]() Since OCH 3 is a more activating substituent than CH 3 (i.e. Here is a useful (but not comprehensive) ranking of activating / deactivating groups: (that is, the more activating substituent “wins”) Rule #1: When two or more substituents are present on an aromatic ring, the directing group will be the most activating substituent. The tricky part is that they each direct to different carbons. Here there are two o-, p- directors: –OCH 3 and –CH 3. Let’s look at a slightly more ambiguous example: p-methylanisole. When Two Or More Substituents Are Present, The Directing Group W ill Be The Most A ctivating Substituent. This gives us the product 2-chloro-1- methoxy-4-nitrobenzene, which indeed is the major product. The –NO 2 is a meta- director, and the positions meta- to the NO 2 happen to also be the positions ortho- to the OCH 3.Īs it turns out, both substituents direct to the same position (C–2).The –OCH 3 is an ortho-, para- director, but since the para- position is already substituted (with NO 2), only the ortho- positions are available.The first thing to do is to analyze each substituent individually. Where does the electrophile react? What’s the directing group, OCH 3 or NO 2 ? Say we try to perform an electrophilic aromatic substitution reaction. Let’s start with 1- methoxy-4-nitrobenzene, which also goes by the name, p-nitroanisole. Here’s a thorny question: What happens when we perform an electrophilic aromatic substitution reaction when there are two substituents on benzene?Īnd say that one of them is an ortho-, para- director and one is a meta- director, and they “direct” electrophiles to different carbons on the ring? Electrophilic Aromatic Substitution With Two Directing Groups: Which Group “Wins” ? (Advanced) References and Further Readingġ.Summary: Electrophilic Aromatic Substitution on Disubstituted Benzenes.Nothing Says “Steric Effects” Quite Like A t-Butyl Group.If Attack At Two Or More Positions Is Possible, Pick The Least Sterically Hindered One.When Two Or More Substituents Are Present, The Directing Group Will Be The Most Activating Substituent.Electrophilic Aromatic Substitution With Two Directing Groups: Which Group “Wins” ?.Having gone through the mechanism of electrophilic aromatic substitution, explored activating and deactivating substituents, and seen the importance of directing groups, let’s now take the opportunity to use these concepts to answer some slightly thornier questions.
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