groups like NO2, SO3 all have those double bonded groups. However, halogens are also able to donate one of their lone pars to the ring through resonance which is characteristic of activating groups. Halogen substituents are slightly deactivating but ortho-para directing. OK. 1) Note that all the groups which would seem to be deactivating meta directors and turn out to be activating o, p directors, -OH and -NH 2, for example, Is deactivating a group meta? We further divide these groups into two categories depending on the way they influence the orientation of attack by the incoming electrophile. Some groups increases the reactivity of benzene ring and are known as activating groups. Halogens are very electronegative. Is a nitro group activating or deactivating? Are halogens electron withdrawing groups? What are activating and deactivating group? Common deactivating groups (not a complete list): NO2, CF3, CN, halogens, COOH, SO3H. Why are halogens slightly deactivating? This video shows you the nature of deactivating groups as meta directors through through logic and structure to help you avoid memorization. 1. Weakly deactivating (O=C)H. Moderately deactivating (O=C)-R. Moderately deactivating (O=C)X. . halogen show both characteristics electron withdrawal through , inductive effect and release through Halogens bonded to benzene ring has three lone pairs. The net effect is that halogens are deactivating but ortho-para directing. Deactivating groups: - NO 3. halogen are unusual in effect on electrophilic aromatic substitution they are deactiviting yet or tho para directing . 2) Why are the halogens deactivating and o, p directing? Nucleophilic Aromatic Substitution Aryl halides do not undergo nucleophilic substitution by either SN1 or SN2 pathways. The only exceptions are the halogens, which are not terribly good pi donors. Activating are Electron Donating groups. The Effect of Substituents on Regio-selectivity via lone pair resonance: including activating groups and weakly deactivating ones (halogens) Ortho and para: 4 resonance contributors and the extra one is relatively stable: all atoms have full octet (except H)-OCH 3 is strongly e-donating due to resonance the only one with complete octet 6e . Terms in this set (8) how do electrons flow in electrophilic aromatic substitution (EAS)? Chapter 17 42Halogens Are Deactivators X Inductive Effect: Halogens are deactivating because they are electronegative and can withdraw electron density from the ring along the sigma bond. An electron donating group ( EDG) or electron releasing group ( ERG, Z in structural formulas) is an atom or functional group that . Halogen atom influence. In electrophilic aromatic substitution reactions, existing substituent groups on the aromatic ring influence the overall reaction rate or have a directing effect on positional isomer of the products that are formed. o Halogens: The electronegativity of a halogen causes it to be an electron withdrawing group via inductive effect. All activating substituents are ortho-para directors. Are EWG activating or deactivating? for the halogens, the inductive and resonance effects run counter to each other, but the former is somewhat stronger the net effect is that halogens are deactivating but ortho-para directing + + + E H Cl ClCl H E E+::::: Activating-Deactivating Organic Lecture Series 44 Di- and Polysubstitution Weakly Ortho-para Directing activating Weakly . Because of their strong-I effect, overall electron density on benzene ring decreases. The halogens deactivate the ring by inductive effect not by the resonance even though they have an unpaired pair of electrons. Its kinda getting a bit picky logic wise, but here is the reasoning straight from Bruice text "The halogens are weakly deactivating substituents. In Electrophilic Aromatic Substitution reactions, O/M/P directing effects help us figure out where to place the incoming electrophile. 20 terms. They deactivate the ring as a result of being highly electronegative groups, pulling electrons away from the benzene ring toward themselves, making the ring less nucleophilic. Electron Donating Groups activate the ring for ortho and para addition. Halogens are very electronegative. The EWG removes electron density from a system, making it less reactive in this type of reaction, and therefore called deactivating groups. Think fluorine, chlorine, bromine. Under identical conditions, Reaction 2 is slower than Reaction 1. In this video you will get to know why halogens are deactivating groups but ortho-para director? Halogens are the one exception in EAS, is the re-aromatization effect exothermic or endothermic? Based on their electronegativity, rank the halonium ions by their electrophilicity. Is no activating or deactivating? For EAS Reactions Electron-Donating Groups = Activating Groups Electron-Withdrawing Groups = Deactivating Groups So all the electron donating groups are considered as activating groups and they direct the incoming group at ortho and para positions. The list with example is given below. Like all strongly and moderately activating substituents, the halogens donate electrons to the ring by resonance and withdraw electrons from the ring inductively. Are halogens electron donating or withdrawing? This resonance directs the donated electrons to the ortho/para positions, making the nitroso group ortho/para directing even as the electronegativity of nitrogen and oxygen make it deactivating. o Halogens: The electronegativity of a halogen causes it to be an electron withdrawing group via inductive effect. Halogen atoms deactivate the aromatic ring towards electrophilic substitution. Video 13 - Halogen Exception Ortho Para Deactivators. 21 terms. shelby_schenck. Moderately deactivating (O=C)OH. This means that inductively they are electron withdrawing. The unpaired pair of electrons gets donated to the ring, but the inductive effect pulls away the s electrons from the ring by the electronegativity of the halogens. . Halogens are electron withdrawing groups due to electronegative nature hence they deactivate benzene ring for electrophilic substitution but are o,p-directing. What are deactivating and activating groups? In the case of the halogens, the resonance and inductive effects operate in opposite directions. E1. o Halogens: The electronegativity of a halogen causes it to be an electron withdrawing group via inductive effect. Thus, the nitro group is a deactivating group. Why chloro group is ortho para directing? There can be electron-donating (activating) and electron withdrawing (deactivating) groups. substituent effects. However, they do not show a strong resonance effect either. The EWG removes electron density from a system, making it less reactive in this type of reaction, and therefore called deactivating groups. If a group increases the stability thereby increases overall reactivity of the electrophilic substitution reaction, then it can be termed as . Is CL activating or deactivating? . Halogens are electron withdrawing groups due to electronegative nature hence they deactivate benzene ring for electrophilic substitution but are o,p-directing. 2 for example, deactivating and meta directing as expected, while others, -NH 2 for example, are activating and o, p directing? But, halogens are also highly electronegative and thus they have strong -I effect. Halogens are an exception of the deactivating group that directs the ortho or para substitution. 1. C=O, N=O, S=O. So, they are deactivating groups. Thus, substituents that activate the benzene ring toward electrophilic attack generally direct substitution to the ortho and para locations. With some exceptions, such as the halogens, deactivating substituents direct substitution to the meta location. Are halogens activating or deactivating? Common deactivating groups (not a complete list): NO2, CF3, CN, halogens, COOH, SO3H. As a result, halogens too are ortho . Substituent Effects. Which substituent is the most activating for EAS? Due to resonance, the electron density on 0- and p- positions is greater than that at the meta position hence, they are 0- and p- directing groups. Halogens bonded to benzene ring has three lone pairs. Based on their electronegativity, rank the halogens by their deactivating power. Are halogens electron withdrawing groups? . oxygen and nitrogen -donors are activating groups. 7. The amide is a less powerful activating group than the simple amino group, -NH 2 since resonance within the N-acetyl group of the amide (see below) competes with delocalisation of the N lone pair into the ring. Deactivating Groups are Meta Directors. However, because of their ability to donate a lone pair of electrons in resonance forms, they are activators and ortho/para directing. Thus, substituents that activate the benzene ring toward electrophilic attack generally direct substitution to the ortho and para locations. The inductive effect of . Because they have three pairs of unshared electrons, halogen atoms can supply electrons toward the ring. This video shows you the unique directing effects of halogens on substituted benzene. alkyls are activating groups. Alkyl groups attached to the aromatic ring also accelerate the reaction. These three electron pairs can cause resonance in benzene ring. the reason they are so reactive is that these elements lack an electron that helps fill and stabilize their electron orbital shell. Strongly activating Weakly activating Deactivating Deactivating; OH: Alkyl: Halogens (F . Note that halogens are also -donors, but they are less effective in this regard than nitrogen or oxygen. Strongly deactivating substituents are meta directors. Ortho, Meta and Para refer to the 1-2, 1-3, and 1-4 relationships between benzene substituents. Halogens are electron withdrawing groups due to electronegative nature hence they deactivate benzene ring for electrophilic substitution but are o,p-directing. Activating groups are substituents that increase the rate of a reaction (by lowering the activation energy). Activating and Deactivating Groups Activating groups are substituents that increase the rate of a reaction (by lowering the activation energy). NH2, OCH3 etc. - CH 3 etc. These observations can be accounted for in the following way. Ortho and Para Directing Groups (Or Activating Groups) Examples: NH 2, NHR, NHCOCH 3, OCH 3, CH 3, C 2 H 5, halogens, etc. Why are halogens deactivating? Both - OCH3 and -Ph are activating, ortho-/para-directing groups. 3. Deactivating groups are substituents that decrease the rate of a . activating groups make electrophilic aromatic substitution faster than in benzene. Halogens are highly reactive non metallic atoms found on the right side of the chemistry periodic table of elements. Moderately Activating-CN, cyano groups-SO 3 H, sulfonates-COOH, carboxylic acid . Halogen Exception! 70 terms. Is CL activating or deactivating? CN. Transcribed image text: As substituents in electrophilic aromatic substitution, halogens are: deactivating ortho/para directors becuase of electronegativity and lone pairs of electrons available o deactivating meta directors because of electronegativity and lone pairs of electrons are available activating ortho/para directors because of the presence of lone pairs activating and meta directors . Is activating or deactivating group? Moderately deactivating. 2. Halogens Are Ortho-, Para- Directors yet Deactivators Halogens are ortho, para directors, however they are also deactivators! Deactivating have an atom with a double bond that is bonded to the ring i.e. Halogens are considered deactivating groups due to the inductive effects of their overwhelming electronegativity withdrawing electrons away from the ring, thus slowing the overall reaction. It's the same situation as we see with halogen atoms. Why are halogens deactivating? Because they are electron withdrawing, halogens are very weak activators. Describes the reason that ring halogens direct electrophilic aromatic substitution to the ortho and para positions but are ring deactivating. 0 P Prateek Full Member Joined May 30, 2010 Messages 418 This means that inductively they are electron withdrawing. In chlorobenzene inductive effect is stronger than the resonance effect. deactivation is characteristic of electron withdrawal ,where as ortha para orientation is characteristic of electron release . Some groups increase the reactivity of benzene ring and are known as activating groups while others which decrease the reactivity are known as deactivating groups. Halogens (F . Hope that makes it simpler! However, because of their ability to donate a lone pair of electrons in resonance forms, they are activators and ortho/para directing. what is the nucleophile in an EAS reaction? But, halogens are also highly electronegative and thus they have strong -I effect. Halogens. Both - OCH3 and -Ph are activating, ortho-/para-directing groups. Deactivating groups are substituents that decrease the rate of a reaction (by increasing the activation energy). CN, - CHO etc, Activating and Deactivating Groups Generalizations These groups have a lone pair atom bonded to the ring. Strongly deactivating substituents are meta directors. Question: 4. All deactivating groups are electron-withdrawing groups. i.e. Why do halogens deactivate benzene? Why is OH more activating than OCH3? Here is short summary answer as to why halogens, being deactivators, are still ortho, para directors: Now, let's discuss this a bit more in detail by first doing a quick overview of the ortho, para and meta directors first. Some groups decreases the reactivity of benzene ring and are known as de-activating groups. halogens are what type of directing . Example: Activating groups: - NH 2 - OH. hannahelise1234. Are EWG activating or deactivating? Similarly if a group reduces the stability of intermediate thereby reduces the reactivity, then it can be termed as deactivating group. 2. The following table summarizes this classification. . Common deactivating groups (not a complete list): NO2, CF3, CN, halogens, COOH, SO3H. Activating-Deactivating (halogens) For the halogens, the inductive and resonance effects run counter to each other, but the former is somewhat stronger. The following table summarizes this classification. With some exceptions, such as the halogens, deactivating substituents direct substitution to the meta location. Activating and Deactivating Groups However, because of their high electronegativities, halogen atoms also tend to remove electrons from the benzene ring. So, they are deactivating groups. Why is amide less activating than amine? 14 terms. are halogens activating or deactivating subsituents? What are activating and deactivating group? Halogens (F, Cl, Br, I) . 3. Is activating or deactivating group? . reily_cannon. The inductive effect is a result of different electronegativities of the carbon in the ring and the atom connected to it. Halogens bonded to benzene ring has three lone pairs. Halogens are EWG's even though they have lone pairs present. The halogens deactivate the ring by inductive effect not by the resonance even though they have an unpaired pair of electrons. Halogens are electron withdrawing groups due to electronegative nature hence they deactivate benzene ring for electrophilic substitution but are o,p-directing. The activation and deactivation of the aromatic ring are caused by inductive or resonance effects (or both). Is COOH a deactivating group? The halogen atoms are the electron-withdrawing group due to greater electronegativity. However, it is so electronegative that this effect is shaded, and overall fluorine makes the ring electron-poor and deactivates it towards electrophilic substitutions. Activating/Deactivating Groups. . Halogens are moderately deactivating. Electron withdrawing groups are meta directors and they are deactivators. Therefore, halogen atoms deactivate the benzene ring towards an electrophilic aromatic substitution reaction. Halogen substituents are slightly deactivating but ortho -para directing. All activating substituents are ortho-para directors. The halogen atoms also possess an electron-donating resonance effect. 7. So, they are deactivating groups. As Table 9.1 shows, the halogens are ortho-para directing, but, unlike other ortho-para directors listed in the table, the halogens are weakly deactivating. These three electron pairs can cause resonance in benzene ring. Halogen atoms show both activating and deactivating characteristics. The inductive and resonance properties compete with each other but overall the resonance stabilization wins and halogens as a result become deactivating ortho para directors.Fluorine directs strongly to the para position (86%) while Iodine directs to ortho and . But, halogens are also highly electronegative and thus they have strong -I effect. The strongest deactivator is 1, and the weakest deactivator is 4. The other halogens are not as electronegative. Generalizations are ortho-para directing and activating ERG ERGs include R, Ar, and C=C Electron-Releasing Groups (ERGs) I Br F CI 5. Electron Withdrawing Groups deactivate the ring for meta addition. Halogen atoms are highly deactivating in nature as these are highly electronegative so they are electron withdrawing in nature and increases the positive charge on the carbon atom of benzene ring. ?Also watchNitration -https://youtu.be/QLc8FvUj1T0Halogen.