Curly Arrows - the curved and barbed arrows you might have seen in reactions have been the language of organic chemistry for over 100 years.
Fundamentally, the arrows represent the path of the electrons. The way they hop between atoms dictates whether a bond will form or break, causing those miraculous molecular transformations.
The meta directors are a class of atoms or a group of atoms that, when attached to an aromatic ring, render it with the ability to direct an incoming electrophile to its meta (third or fifth) position in an electrophile aromatic substitution reaction.
Learning Objective: To study the ambident nucleophiles and how and from which end they attack the substrates to undergo chemical reactions.
Skill Level - Intermediate
Prerequisites:
Learning Objective: To study the three types of addition reactions that nucleophiles undergo.
Skill Level - Intermediate
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Learning Objective: To study the three broad types of displacement reactions that nucleophiles undergo.
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Learning Objective: To learn about the trend and order of nucleophilicity for the p-block elements in the periodic table
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Electronegativity trend of the elements from the Periodic table
Learning Objective: To study the nucleophiles that function as sigma bond donors that form Carbon, Hydrogen, and Halogen bonds with the substrate.
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Electronegativity trend of the elements from the Periodic table
Learning Objective: To study the behavior of pi bonds containing nucleophiles seen in organic chemistry reactions.
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Learning Objective: To study the types of nucleophiles commonly encountered in organic chemistry and their behavior in a chemical reaction.
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Learning Objective: To study the formation and different categories of electrophiles commonly seen in organic chemistry.
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Learning Objective: To study the various examples of organic reactions where the leaving group departs from a molecule and also understand its various types.
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Displacement and Elimination type of reaction (Chapter- Common Types of Reactions)
Learning Objective: To compare various groups on their ability to break off or 'leave' from a molecule and, in that process, classify them as good or bad leaving groups.
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Learning Objective: To determine the factors responsible for the stability of a leaving group. These factors decide whether the leaving group is good or bad.
Learning Objective: To study lone pair's role in chemical reactions as electron donors.
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Learning Objective: To study the impact of lone pair on a molecule's polarity and dipole moment.
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Learning Objective: To study how the presence of a lone pair on the central atom of a molecule contributes to Hydrogen bonding, a type of intermolecular attractive force.
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Learning Objective: To investigate how the presence of a lone pair in a molecule affects its bond angle and, therefore, affects its shape.
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| Lewis Base | Nucleophile | Lowry Bronsted Base |
|---|---|---|---|
Nature | Donates Electron Pair to any electron-deficient center. Nucleophiles and Lowry Bronsted bases are Lewis bases. | Donates Electron Pair, mostly forming bonds with carbon. The term is commonly used to describe organic chemistry reactions. |
Nucleophiles are electron-rich species that can donate a pair of electrons and form a new covalent bond with an electron-deficient counterpart called the electrophiles. That is why electrophiles are referred to as lovers of electrons.
The nucleophiles donate electrons as lone pairs, pie bonds, or sigma bonds.
Read- What are nucleophiles?
Organic chemistry reactions involve electron-transfer reactions, and many of them use reaction mechanisms to show how electrons flow. This electron flow is typically represented using a double-sided curly arrow.
Nucleophiles are electron-rich molecules and anions that donate an electron pair to the electron-deficient counterparts, the electrophiles, and form covalent bonds with them.
While nucleophiles donate two electrons in exchange for forming two-electron covalent bonds with the electrophiles, the negative charge due to the two electrons is not obvious in many instances. Neutral molecules like Benzene, water, and ammonia can act as nucleophiles.
A broad way to categorize nucleophiles is as charged or neutral (uncharged).
When asked to explain ‘What is a nucleophile?’, it is common to see an answer like –
Free Radical | Lone Pair | Bond Pair |
|---|---|---|
Homolytic bond cleavage generates two free radical species. A free radical is an atom carrying an unpaired electron, denoted as A. (atom symbol A with a dot for an electron on the superscript). | The valence electrons of an atom that did not participate in any covalent bond formation reaction exist as a lone pair. However, not all nonbonding electrons are lone pairs. It is denoted as two dots for two electrons above the atom’s symbol A.. |
| Reactant | Reagent | Catalyst |
|---|---|---|---|
Definition | A substance that participates and undergoes a structural change in a chemical reaction is a reactant. | A reagent is a substance added to reactions intending to bring chemical changes. Sometimes it tests a reaction's progress and product formation(s). Therefore, it may or may not be consumed in a reaction. |
Two electron-deficient species on opposite sides of heterolytic cleavage: one departs without the bond pair, the other arrives to form a new bond.
Electron-deficient after departure. Classic example: H+ leaving an aromatic ring during electrophilic substitution.
Electron-deficient by nature, either neutral or positively charged. Common examples: H+, CH3+, NO2+, AlCl3.
An electrofuge is a leaving group that is formed due to the heterolytic breakage of a bond, where after the cleavage, it leaves without the bond pair of electrons, and is therefore electron-deficient.
Electrophiles are electron-deficient species, which may be neutral or charged because of heterolytic bond cleavage. Their primary nature is to attract electrons from other electron-rich counterparts and form a new bond.
The departing partner. An electrofuge leaves a substrate. It is what comes off when a new electrophile attaches.
The arriving partner. An electrophile attacks a substrate that is electron-rich. It is what attaches when an electrofuge leaves.
Becomes electron-deficient at the moment of departure. The bond pair stays with the substrate; the electrofuge leaves with no electrons from the broken bond.
Is already electron-deficient before arrival. That is what drives it to seek an electron-pair from a nucleophile or an electron-rich substrate.
The classic example is hydrogen as an electrofuge, H+. The loss of hydrogen as H+ is common in aromatic electrophilic substitution, where the incoming electrophile displaces H+ as the leaving group.
Example: in the nitration of benzene, the incoming electrophile is NO2+, and H+ is the electrofuge.
Common electrophiles include both charged and neutral species. Charged: H+, CH3+, NO2+. Neutral but electron-deficient: CH3COCl (acyl chloride), AlCl3 (Lewis acid).
Examples: H+, CH3+, NO2+, CH3COCl, AlCl3.
Electrofuges are formed in elimination and substitution reactions involving electrophiles. Wherever an electrophile bonds to a substrate by displacement, the displaced group is the electrofuge.
Electrophiles participate in addition and substitution reactions alongside nucleophiles, displacing an electrofuge in the substitution case and adding across a multiple bond in the addition case.
H+ is released from the aromatic ring after the electrophile has bonded to a ring carbon. This restores the aromatic pi system. The departing H+ is the electrofuge.
NO2+, Br+, R+, RC(=O)+, and SO3 all attach to the aromatic ring at the start of the reaction. Each is the electrophile. The ring's pi electrons attack the electrophile.
Mnemonic: ‘-fuge flees, -phile loves.’ The suffix ‘-fuge’ comes from Latin fugere, to flee (think of how a centrifuge flings things outward). The suffix ‘-phile’ comes from Greek philos, loving. An electro-fuge flees the bond without electrons. An electro-phile loves electrons and forms a new bond to them.
Why this works: Both species are electron deficient, so the suffix is what tells them apart. One is in the leaving direction, the other in the arriving direction.
In the nitration of benzene with HNO3/H2SO4, the NO2+ ion bonds to the ring and an H+ leaves. The H+ that leaves is which species?
Both terms describe electron-deficient species that arise in heterolytic reactions, but they sit on opposite sides of the bond-making event. An electrofuge is what leaves a substrate without the bond pair after heterolytic cleavage; an electrophile is what arrives at a substrate looking for an electron pair to form a new bond [1]. Identifying which species plays which role is one of the basic mechanism-reading skills in organic chemistry.
| Nucleofuge | Nucleophile |
|---|---|---|
Definition | It is a leaving group that leaves a reactant (substrate) molecule by withdrawing the electron pair of the C-C bond and breaking it.
| Nucleophiles are electron-rich species that donate electron pair to electron-deficient species and forms a new C-C bond.
|
Nature |
Carbon is naturally inclined to form new bonds, and in this quest, it may break away from the old ones. The atom or group of atoms that leaves the carbon chain to make way for the new bond is called the leaving group(s).
Such a bond dissociation can happen from a saturated, unsaturated, or carbonyl carbon.
Radicals | Electrophiles |
|---|---|
Free Radicals are the by-product of homolytic bond cleavage. | Electrophiles are the by-product of heterolytic bond cleavage. |
The two-electron bond breaks in half, dividing the electrons equally between the two atoms to form two free radicals. Therefore, free radicals are atoms or molecules carrying a single electron. |
Nucleophiles are an atom or a group of atoms that are richer by two electrons and donate these electrons to electron-deficient species, the electrophiles.
Donating the electrons from the nucleophile to the electrophile creates a new two-electron covalent bond.
Pre-Requisite Reading: Nucleophiles, Electrophiles
Electrophiles love electrons, and without them, they become unstable. And to reach a stable state, the electrophiles accept electrons from electron-rich nucleophiles.
Therefore, the electrophiles are electron-deficient species and acceptors of electrons.
Organic chemistry and human beings both pursue betterment and advancement.
Humans engage in welfare activities to improve the well-being of others, tackle inequality, and create strong bonds. The same principle is also observed in organic chemistry.
Lone pair is a set of electrons present in an atom’s valence shell that did not participate in a covalent bond formation reaction; therefore, they are also called the non-bonding electrons.
While drawing the molecules’ structure, the lone pair electrons on shown as dots (..) above the atom.
Lone pair is a set of electrons present in an atom’s valence shell that did not participate in any bond-formation reaction. Since they refuse to bond with the other atoms, they are also called the non-bonding electrons. While drawing the molecules’ structure, the lone pair electrons on shown as dots (..) above the atom.
