Related Experiment Video
Updated: Jun 27, 2026
09:45
A Protocol for Safe Lithiation Reactions Using Organolithium Reagents
Published on: November 12, 2016
Relative basicities of ortho-, meta-, and para-substituted aryllithiums
Joanna Gorecka-Kobylinska1, Manfred Schlosser
1Institute of Chemical Sciences and Engineering, Ecole Polytechnique Federale (EPFL-BCh), CH-1015 Lausanne, Switzerland.
The Journal of Organic Chemistry
|November 28, 2008
Summary
The study assessed the basicity of substituted aryllithiums, finding substituent effects on basicity depend on their position relative to the lithium atom. These findings offer insights into organometallic chemistry and substituent effects.
Area of Science:
- Organometallic Chemistry
- Physical Organic Chemistry
Background:
- Aryllithium compounds are crucial in organic synthesis.
- Understanding substituent effects on aryllithium basicity is key to controlling reactivity.
Purpose of the Study:
- To quantify the relative basicities of aryllithiums with various ortho, meta, and para substituents.
- To correlate these basicities with gas-phase protonation enthalpies of aryl anions.
Main Methods:
- Equilibration of aryllithium pairs with aryl halides in pentane/tetrahydrofuran mixtures at low temperatures (-50 to -100 °C).
- Determination of equilibrium constants to calculate "basicity" (protodelithiation) increments (DeltaDeltaG).
Main Results:
- A linear correlation was observed between DeltaDeltaG values and gas-phase protonation enthalpies.
- The correlation's strength was position-dependent, with ortho, meta, and para substituents mirroring "naked" aryl anion effects at 36%, 30%, and 25%, respectively.
Conclusions:
- The basicity of aryllithiums is influenced by substituent type and position.
- These findings highlight the interplay between electronic and positional effects in organolithium chemistry.
Related Concept Videos
01:11ortho–para-Directing Activators: –CH3, –OH, –NH2, –OCH3
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
01:14Directing Effect of Substituents: ortho–para-Directing Groups
Ortho–para directors are substituent groups attached to the benzene ring and direct the addition of an electrophile to the positions ortho or para to the substituent. All electron-donating groups are considered ortho–para directors. They donate electrons to the ring and make the ring more electron-rich. The ring is therefore susceptible to the addition of electrophiles. Substituents such as amino, hydroxy, or alkoxy, containing lone pairs on the atom adjacent to the ring, donate electrons...
01:24ortho–para-Directing Deactivators: Halogens
Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
01:18Basicity of Aromatic Amines
The basicity of aromatic amines is much weaker than that of aliphatic amines due to the involvement of the lone pair of electrons over the N atom in resonance with the aryl rings. Generally, the electron-donating ability of any substituents on the aryl ring of aromatic amines increases the basicity of the amine by increasing electron density, and hence the availability of lone pair on the nitrogen. On the other hand, electron-withdrawing functional groups on the aryl ring of amines decrease the...
03:51Molecular Orbital Theory II
Molecular Orbital Energy Diagrams
01:09Directing Effect of Substituents: meta-Directing Groups
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...