An important element in organic chemistry is the effect of substituents. The properties of a molecule change depending on which functional group is attached to the alkyl chain or benzene ring.
Two particularly important effects of substituents are the induction effect (I effect) and the coordination effect (R effect). The acidity of the molecule varies depending on the substituents attached to it. It also depends on whether the substituent is attached to an alkyl chain or a benzene ring.
There are two types of substituents: electron donating and electron withdrawing. Electron-donating groups donate electrons and electron-withdrawing groups withdraw electrons. By identifying them, we can deduce the reactivity of the molecule.
So make sure you understand the principles of induction and resonance effects. Once you understand the nature of the substituents and learn to distinguish between electron-donating and electron-withdrawing groups, you can determine the acidity of the molecule.
Index
- 1 Differences between induction effect (I effect) and resonance effect (R effect)
- 2 The acidity varies with the degree of electronegativity due to the inductive effect
- 2.1 Limited influence of electron withdrawing groups
- 3 Resonance effects are responsible for electron displacement
- 3.1 The resonance effect is stronger than the inductive effect
- 3.2 How to distinguish between electron-donating and electron-withdrawing groups in aromatic rings
- 4 The acidity of the benzene ring depends on the substituents
- 4.1 Coordination structures change the stability of electrons
- 5 Electronegativity and coordination contribute to the stability of the compound
Differences between induction effect (I effect) and resonance effect (R effect)
First: what is the inductive effect (I-effect)? And what is the resonance effect (R-effect)? Let's think of both as effects caused by the functional groups attached to the molecule. Depending on which substituents are attached to the molecule, there are many differences, such as different acidity.
The differences between the two are as follows.
- Inductive effect: σ-bond effect (single bond)
- Resonance effect: π-bond effect (double and triple bonds)
Electron orbitals include the s and p orbitals, and these orbitals form bonds. Among the bonds formed by these s and p orbitals, the single bond is the σ bond.The substitution effect of the σ-bond is the induction effect.
On the other hand, some molecules form double or triple bonds. The part of the molecule that forms a double or triple bond is called a π bond. When a pi bond is present, one can write coordination structures.The coordination effect results from the coordination of the substituent, which changes the orientation (reactivity on the benzene ring) and the acidity of the molecule.
In general, understand that the induction effect (I effect) affects the alkyl chain and the resonance effect (R effect) affects the benzene ring.
The acidity varies with the degree of electronegativity due to the inductive effect
The inductive effect affects the single bond (σ bond). When does the inductive effect occur? Occurs when an atom (or molecule) with a high degree of electronegativity is bound.
Linkage with an alkyl chain is particularly important. An alkyl chain without double or triple bonds does not cause coordination. For this reason,For alkyl chains we only need to consider the inductive effect.
When an atom forms a bond with a high degree of electronegativity, it strongly attracts electrons. This causes the molecule to develop both a positive and a negative charge even though it is the same molecule. This is called polarization. Water, ammonia and hydrogen chloride are known to be polarized.
Polarization due to differences in electronegativity also occurs in alkyl chains.When a high electronegativity substituent is attached to an alkyl chain, it leads to a difference in acidity.
An example of an acidic substance is acetic acid. When a carboxylic acid is present, it exhibits acidic properties. However, even if it is the same carboxylic acid, the acidity will vary depending on the substituents present on the surrounding carbon.
For example, what happens when a chlorine atom, a halogen, bonds with acetic acid (CH)?3COOH); In this case, the result is as follows.
When a chlorine atom is attached, the electrons are attracted to the chlorine atom. This means that chloroacetic acid has a stronger negative charge than carboxylic acid. This means that the acidity of chloroacetic acid is higher.
Electrons are withdrawn from the halogen, making chloroacetic acid more acidic than carboxylic acid.
The effect of the electron-withdrawing substituent is an inductive effect. This effect is responsible for acid strength. Obviously, the more halogens are bound, the greater the acidity.
As explained in the acid example, it also affects basicity in the same way. The inductive effect depends on the degree of basicity.
For functional groups with strong electronegativity, the inductive effect is involved in many cases. When an oxygen or nitrogen atom or a halogen atom is attached to an alkyl chain, it causes an inductive effect and decreases the electron density.
- Nitro Group (-NO2)
- Aminogruppe (-NH2)
- Cyan Group (-CN)
- carbonyl group (-CO)
- Carboxygruppe (-COOH)
- Sulfone group (-SO3THE)
- Grupo Methoxy (-AND3)
- Hydroxyl group (-OH)
- Halogen (-Cl, -Br, -I)
All attract electrons attached to the alkyl chain, causing the inductive effect.Functional groups containing oxygen or nitrogen atoms or halogens are all electron withdrawing groups.
Limited effect of electron withdrawing groups
What is the inductive effect of the electron withdrawing group? Let's be clear that this is limited.
Although electronegativity attracts electrons, the effect is small over long distances.For neighboring carbon atoms to which the electron-withdrawing group is attached, there is an effect due to the inductive effect. However, as the distance increases, the effect of electronegativity decreases.
Although the inductive effect reduces the electron density, the area of influence is small.
-The more carbon atoms there are, the higher the electron density
For reference, the presence of carbon atoms increases the electron density. Unlike oxygen, nitrogen and halogen atoms, carbon atoms repel electrons. This is the opposite of electron withdrawing.
So when many carbon atoms are bonded together, the electron density is greater.
Resonance effects are responsible for the displacement of electrons
The inductive effect on alkyl chains is simple. The inductive effect (Effect I) is the reduction of the electron density due to the binding of functional groups with high electronegativity. This leads to a higher degree of acidity (or basicity).
The resonance effect (R effect), on the other hand, is a bit more complicated. Unlike the induction effect, which only needs to consider the effects of single bonds, the resonance effect requires consideration of the effects of double and triple bonds. The result of the π bond is the resonance effect.
Between these double bondsThe resonance effect has a strong effect on the orientation and acidity of aromatic compounds (compounds with benzene rings).It is also responsible for the reaction rate of organic chemical reactions.
For compounds with conjugated structures, the coordination effect must be taken into account. In general, we can think of resonance effects as being related to the reactivity of the benzene ring.
The resonance effect is stronger than the inductive effect
Oxygen and nitrogen atoms are typical examples of electron-withdrawing groups. Thus, when there are hydroxy groups (-OH), methoxy groups (-OCH).3) and amino groups (-NH2) are attached to the alkyl chain, they become electron-withdrawing groups. Any of these substituents can be considered an electron withdrawing group.
In the case of aromatic compounds, however, the situation is different. Sometimes the substituent becomes an electron donating group and sometimes an electron withdrawing group. And that's because they resonate.
The more coordination structures you can write, the more stable the connection. When there is resonance, the electrons can move with it to many places. This is called electron delocalization. The greater the degree of delocalization, the more stable the electron state becomes.
To be able to design coordination structures, it is important that the compound has a double bond. Because the benzene ring has double bonds, we can draw coordination structures for any aromatic ring compound. For example, here is the aniline coordination.
If we focus on the nitrogen atom of aniline, we can see that the electrons are pushed away from the nitrogen atom toward the benzene ring. In other words,The nitrogen of aniline acts as an electron donating group.
Since it is a nitrogen atom, there is a force that attracts the electrons through induction. However,Compared to the inductive effect, the effect of electron delocalization due to resonance is much stronger.This makes the amino group on the benzene ring an electron-donating group.
How do you distinguish electron-donating and electron-withdrawing groups in aromatic rings?
How do we distinguish electron-donating and electron-withdrawing groups in the benzene ring? To do this, look for double (or triple) bonds in the substituents.
The following substituents, for example, are involved as electron donating groups on the benzene ring.
- Grupo Methoxy (-AND3)
- Hydroxyl group (-OH)
- Aminogruppe (-NH2)
If we focus on the atoms directly attached to the benzene ring (oxygen and nitrogen atoms), we find that they are all single bonds. Therefore, these substituents are electron-donating groups on the benzene ring.
On the other hand, what if the substituent contains a double (or triple) bond? In this case, they act as electron withdrawing groups.
- carbonyl group (-CO)
- Carboxygruppe (-COOH)
- Sulfone group (-SO3THE)
- Nitro Group (-NO2)
- Cyan Group (-CN)
The presence of a double bond (or triple bond) allows electrons to be attracted by coordination to the substituent group. This makes it an electron withdrawing group.
When an oxygen or nitrogen atom is attached to the substituent, it becomes an electron-donating group if the substituent has only single bonds.Secondly,When a substituent is attached to a double bond (or triple bond), it becomes an electron withdrawing group.Although there are exceptions, this is a rough understanding.
The acidity of the benzene ring depends on the substituents
Although it is an electron withdrawing group in an alkyl chain, it can be an electron donating group in an aromatic ring compound. This fact must first be understood. It can be more complicated with the resonance effect than with the inductive effect.
So why is it important to understand the resonance effect (R-effect) in aromatic compounds? This is because it is acidity. Although orientation (which part of the benzene ring triggers the chemical reaction) also changes, let's focus on acidity.
Even with the same aromatic compound, the acid content changes depending on the substituent.For example, phenolic compounds are listed in the following order of acidity.
Why does this difference arise?
Halogens attract electrons by induction. Therefore, it is understandable that they are more acidic than phenol. Carbon atoms also eject electrons. Because the carbon atom is an electron-donating group, its acidity is lower than that of phenol.
On the other hand, what about nitro and methoxy groups? These two functional groups should not be considered only for their inductive effects. Since the resonance effect is very strong, we must consider the acuity while considering the resonance.
Coordination structures change the stability of electrons
For phenol to be acidic,We can assume that the more stable it is after it is converted into an ion, the stronger the acidity.In this case, the nitro group (p-nitrophenol) resonates as follows.
After phenol becomes an acid, various coordination structures can be written. Electrons are also shifted to the nitro group. The acidity of p-nitrophenol is high because of its stability when it becomes acid.The presence of an electron-withdrawing group increases acidity.
On the other hand, what about the presence of a methoxy group? The methoxy group on the aromatic ring acts as an electron donating group. This will reduce the sharpness compared to the previous example.
When coordinated to the electron-donating methoxy group, the result is as follows.
The methoxy group donates electrons to the benzene ring,This creates a negatively charged carbon and an oxygen atom next to each other.When they become ions in this state, negative charges coexist.
Negative and negative charges repel each other. This means that the coordination structure is unfavorable since phenol is acidic when ionized. Because of this, the presence of an electron donating group on the benzene ring reduces its acidity.
-The tuning effect changes the alignment of Ortho, Meta and Para
Not only is sharpness affected by the resonance effect, but so is orientation. Orientation is a tool for predicting which part of the benzene ring will undergo an organic chemical reaction.
In the benzene ring there are ortho, meta and para positions of the substituents. The position at which substituents are attached in an aromatic compound depends on the electron-donating and electron-withdrawing groups. Furthermore, the reactivity of the aromatic compound changes with a different orientation.
These are also affected by the resonance effect (R-effect).
electronegativityand coordination contribute to the stability of the connection
Various substituents are attached to molecules. Depending on the type of functional group, the molecule exhibits different properties.
The most obvious is the inductive effect (I-effect). The higher the electronegativity, the more electrons the substituent will attract. As a result, the acidity of the molecule will be different. The difference in acidity is very important because it causes not only a difference in resistance to acidity and alkalinity, but also a difference in reactivity.
However,A substituent that participates in the induction effect as an electron-withdrawing group can act as an electron-donating group in aromatic compounds.Therefore, it is important to be able to tell the difference between an electron-donating group and an electron-withdrawing group.
The resonance effect is stronger than the inductive effect. Therefore, depending on which substituents are on the benzene ring, the acidity and orientation of the molecule can vary widely.
The nature of the molecule depends largely on the substituents. Depending on whether the substituent is attached to an alkyl chain or a benzene ring, the properties of the substituent change. It is important to understand this fact.
FAQs
What is inductive effect with electron withdrawing and donating groups? ›
In chemistry, the inductive effect in a molecule is a local change in the electron density due to electron-withdrawing or electron-donating groups elsewhere in the molecule, resulting in a permanent dipole in a bond. It is present in a σ (sigma) bond, unlike the electromeric effect which is present in a π (pi) bond.
Which inductive effect is shown by electron withdrawing group? ›When an electron withdrawing or electron releasing group is attached to carbon chain, polarity is induced on the carbon atom and on the substituent attach to it. This permanent polarity is due electron displacement due to difference in electronegativities this is called inductive effect or I effect.
What effect is electron withdrawing or donating? ›An electron donating group (EDG) has the net effect of increasing electron density in a molecule through the carbon atom it is bonded to. By increasing electron density on adjacent carbon atoms, EDGs change the reactivity of a molecule: EDGs make nucleophiles stronger.
What are the electron withdrawing groups and electron donating groups? ›The important electron withdrawing groups should be remembered for NEET examination point of view are halogens (F, Cl), nitriles CN, carbonyls RCOR' and nitro groups NO2. The electron donating groups are alkyl groups, alcohol groups and amino groups.
What is the difference between electron donating and electron withdrawing? ›electron withdrawing substituents increase the Lewis acidity of acidic sites by making those sites more electron deficient while electron donating substituents tend to decrease Lewis acidity by making sites less electron deficient.
What is the correct order of the inductive effect? ›The correct order of increasing electronegativity of atom is N<O<F and hence the correct order of negative inductive effect is −NR2<−OR<−F i.e. option (c)
Which groups show inductive effect? ›The electron withdrawing inductive effect is also called as −I effect. Therefore, the alkyl groups show +I effect and the halogens or other electronegative groups show −I effect .
What are the two categories of inductive effect? ›There are two types of inductive effect i.e. – I effect and +I effect.
Which of the following group shows inductive effect? ›Hint: Electron withdrawing group shows negative inductive effect and electron releasing group shows positive inductive effect.
What makes a group electron withdrawing? ›Electron withdrawing group (EWG): An atom or group that draws electron density from neighboring atoms towards itself, usually by resonance or inductive effects. localized on the nitrogen atom. resonance, as demonstrated by this resonance hybrid.
What is electron donating effect called? ›
The polarization of a σ bond due to electron withdrawing or electron donating effect of adjacent groups or atoms is referred to as inductive effect.
What are 3 examples of electron withdrawing groups? ›Examples of electron withdrawing groups: -CF3, -COOH, -CN. Electron withdrawing groups only have one major product, the second substituent adds in the meta position. Again, this can be explained by the resonance forms of the carbocation intermediates.
How do electron donating groups affect chemical shift? ›An electron donating group such as MeO- (+M effect), increases the electron density in o- and p- positions. As result, the chemical shift of the o-proton (δ=6.79 ppm) and p- proton (δ=6.73 ppm) appear more shielded than the benzene proton (δ=7.28 ppm).
Which is more stable electron withdrawing or donating? ›An electron donating group! A positively charged species such as a carbocation is very electron-poor, and thus anything which donates electron density to the center of electron poverty will help to stabilize it. Conversely, a carbocation will be destabilized by an electron withdrawing group.
How do you memorize electron withdrawing and donating groups? ›If you want to go a little further in the homologous series, remember this sentence: Hitesh and Harish Organized Ninja championship with Duke, Uma and Dinesh. These mnemonics will never let you forget the electron withdrawing and donating groups.
Do electron withdrawing groups increase stability? ›6. Factor #5: Electron-Withdrawing Groups (Inductive Effects) Stabilize Negative Charge. This one falls more into the auspices of “opposite charges attract”. A negative charge that is adjacent to an atom with electron withdrawing groups on it will be much more stable than an equivalent atom that is not.
Which has higher inductive effect? ›It is because the methyl group has a positive inductive effect; this effect is due to the higher electronegativity of carbon than hydrogen, which attracts the electron from hydrogen and becomes slightly negative and push the electrons towards other groups.
Which order of inductive effect is incorrect? ›(C) Order: −O−>−CHMe2>D>H This is incorrect order because inductive effect of H is more than that of D. Because of one extra neutrons size of D is higher than H as a result this increased size reduces electronegativity of D .
What are the characteristics of the inductive effect? ›The inductive effect, often known as “the -I Effect,” is a gap-established phenomenon in which the pricing of a chemical bond impacts the orientation of adjacent bonds in a molecule, resulting in an eternal kingdom of polarisation. The electron density isn't homogeneous when atoms from two components make a bond.
What are the 3 common types of inductive arguments? ›There are three types of inductive arguments: generalizations, analogical arguments, and causal arguments.
What is inductive effect in simple words? ›
When a covalent bond is formed between atoms of different electronegativity , the electron density is more towards the more electronegative atoms of the bond,such a shift in electron density is called as inductive effect.
What are the three parts of inductive reasoning? ›In inductive research, you start by making observations or gathering data. Then, you take a broad view of your data and search for patterns. Finally, you make general conclusions that you might incorporate into theories.
Which groups show positive inductive effect? ›The inductive effect refers to the phenomenon wherein a permanent dipole arises in a given molecule due to the unequal sharing of the bonding electrons in the molecule. Positive inductive effect of alkyl group: In an alkyl group, carbon is linked to hydrogen atoms. Carbon is more electronegative than hydrogen.
What is the effect of electron releasing group and electron withdrawing group on acid strength and basic strength of a compound? ›In general, electron withdrawing groups increase the acidity of carboxylic acids while electron donating groups decrease the acidity of the carboxylic acid.
What is the effect of electron withdrawing group and electron donating group on the acidity of phenol? ›Electron-withdrawing substituents make a phenol more acidic by stabilizing the phenoxide ion through delocalization of the negative charge and through inductive effects. The effect of multiple substituents on phenol acidity is additive.
Which functional group has electron donating inductive effect? ›The function group that has electron donating or positive inductive effect is −CH3 Since, the positive inductive effect is due to the presence of an electron donating groups within the polar bond.
Which group has strongest inductive effect? ›Therefore the carbon with sp hybridization (as in alkynes) shows greatest inductive effect.
Which of the following group has more inductive effect? ›It is because the methyl group has a positive inductive effect; this effect is due to the higher electronegativity of carbon than hydrogen, which attracts the electron from hydrogen and becomes slightly negative and push the electrons towards other groups. I hope it helps.
Which groups have negative inductive effect? ›The negative inductive effect of the groups - NH3, OH, CN, CONH2, SO3H follows the order (A) NH3 > CN > SO H > OH > CONH2 (B) NH; > CONH, > OH > SOZH > CN (C) OH > NH3 > CONH2> SO3H > CN (D) NH3 > CN > SO3H > CONH, > OH.
Do electron withdrawing or donating groups increase acidity? ›An electron withdrawing group increases the acidity carboxylic acid. It disperses negative charge by inductive/ resonance effect and stabilizes the carboxylate ion.
What is the effect of electron donating and electron withdrawing group on the acidity of a carboxylic acid? ›
The presence of groups near the -COOH group of a carboxylic acid has an effect on acidity. Generally, electron-withdrawing groups increase acidity by increasing the stability of the carboxylate ion. The presence of, electron-donating groups decrease acidity by destabilizing the carboxylate ion.
Why do electron donating groups increase acidity of acid? ›The conjugate base of benzoic acid is destabilized by electron-donating groups (EDG). This makes the acid less acidic by pushing more electron density toward the negative charge in the carboxylate. Electron-donating groups activate the benzene ring to electrophilic attack and make benzoic acids less acidic.
Why do electron withdrawing groups increase stability? ›Factor #5: Electron-Withdrawing Groups (Inductive Effects) Stabilize Negative Charge. This one falls more into the auspices of “opposite charges attract”. A negative charge that is adjacent to an atom with electron withdrawing groups on it will be much more stable than an equivalent atom that is not.
How do electron withdrawing groups affect bond strength? ›The point is that electron withdrawing exerted by a group attached to the carbonyl reflects to the other side, but not subtracting electron density, opposite decreasing the weight of -O---C+. Bond order increases and thus frequency increases.
Do electron withdrawing groups increase reduction potential? ›Firstly, it was shown that electron-withdrawing groups increased the potential of the molecule, while electron donating tended to decrease it.
What is the inductive effect of electron donation? ›When a chemical species with the tendency to release or donate electrons, such as an alkyl group, is introduced to a carbon chain, the charge is relayed through the chain, and this effect is called the positive inductive effect or the +I effect.
What is the electron donating inductive effect? ›Inductive effect: The effect on electron density in one portion of a molecule due to electron-withdrawing or electron-donating groups elsewhere in the molecule.
How do you tell if a functional group is electron withdrawing or donating? ›Usually, if a group next to a molecule which has pi-bond, is more electron negative, then it is an electron withdrawing group. And if the group next to a molecule which has pi-bond is less electron negative, then it is an electron donating group.