Directing Effects
Directing Effects - Related Videos
01:18
Directing and Steric Effects in Disubstituted Benzene Derivatives
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2023
When disubstituted benzenes undergo electrophilic substitution, the product distribution depends on the directing effect of both substituents. When the directing effects of both substituents reinforce each other, a single product is obtained. For example, bromination of p-nitrotoluene occurs ortho to the methyl group and meta to the nitro group, which is the same position, resulting in a single product. However, if the directing effects of the two groups oppose each other, the more strongly...
01:09
Directing Effect of Substituents: meta-Directing Groups
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2025
Substituents on the benzene ring that direct an incoming electrophile to undergo substitution at the meta position are called meta directors. All meta directors either have a positive charge on the atom directly bonded to the ring or a partial positive charge. These groups function by withdrawing electrons from the ring through inductive and resonance effects. Consider the carbocation intermediates formed upon the addition of an electrophile on nitrobenzene at the ortho, meta, and para...
09:20
Vectors in Multiple Directions
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2023
Source: Nicholas Timmons, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA This experiment demonstrates how vectors add and subtract in multiple directions. The goal will be to analytically calculate the addition or subtraction of multiple vectors and then to experimentally confirm the calculations. A vector is an object with both magnitude and direction. The magnitude of a vector is simply denoted as the length,...
06:16
An Experimental Approach to Investigating Effects of Artificial Light at Night on Free-Ranging Animals: Implementation, Results, and Directions for Future Research
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Cited by 9 •
2022
Artificial light at night (ALAN) has wide-reaching biological effects. This article describes a system for manipulating ALAN inside nest boxes while monitoring behavior, consisting of LED lights coupled to a battery, timer, and audio-capable infrared video camera. Researchers could employ this system to explore many outstanding questions regarding the effects of ALAN on organisms.
11:37
Using Sniper-Cas9 to Minimize Off-target Effects of CRISPR-Cas9 Without the Loss of On-target Activity Via Directed Evolution
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Cited by 21 •
2019
Here, we present a protocol to optimize CRISPR-Cas9 to achieve a higher specificity without the loss of on-target activity. We use a directed evolution approach called Sniper-screen to find a mutant Cas9 with the desired characteristics. Sniper-Cas9 is compatible with truncated single-guide RNAs and delivery in a ribonucleoprotein format, well-known strategies for achieving higher specificities.
FAQs
Electron-donating substituents influence the arenium ion intermediate formed during electrophilic aromatic substitution. For ortho and para attack, resonance structures can provide greater stabilization from the attached group, making those pathways more favorable than meta attack. This stabilization helps explain both the preferred orientation and the tendency of these substituents to increase the ring’s reactivity.
Electron-withdrawing groups alter the aromatic ring through inductive or resonance effects that reduce its electron availability. These effects make electrophilic substitution less favorable overall and can particularly destabilize intermediates associated with ortho and para attack. Meta substitution therefore becomes the preferred orientation because it avoids the least favorable electronic interactions produced by the attached group.
Halogens demonstrate that reaction rate and substitution position are separate consequences of electronic effects. They deactivate the aromatic ring, so substitution is less favorable overall, yet they direct incoming electrophiles to the ortho and para positions. Recognizing this exception prevents chemists from assuming that every deactivating substituent must produce meta substitution.
A synthesis can be planned by evaluating the substituent already present before each electrophilic aromatic substitution. Its electronic behavior indicates whether the next group is expected at an ortho, meta, or para position and whether the ring is activated or deactivated. Applying this reasoning sequentially helps design routes to substituted aromatic compounds with the desired arrangement of groups.
First, identify the substituent attached to the aromatic ring. Next, determine whether its influence is electron-donating or electron-withdrawing, then use the corresponding directing preference to select the likely position of the incoming electrophile. Finally, consider whether the group activates or deactivates the ring, since that affects how favorable the substitution is overall.
Directing effects connect electronic structure with the products formed in aromatic reactions. They help explain why the same incoming electrophile can produce different positional isomers depending on the group already attached to the ring. This predictive framework is especially useful when interpreting electrophilic aromatic substitution and choosing efficient sequences for constructing substituted aromatic compounds.