Since the resonance stabilization of the phenolate conjugate base is much greater than the stabilization of phenol itself, the acidity of phenol relative to cyclohexanol is increased. If this spring is cut in half, does the resulting half spring have a force constant that is greater than, less than, or equal to kkk ? Experts are tested by Chegg as specialists in their subject area. 3) Polarizability The more polarizable an atom is, the more nucleophilic it will be. The ammonium ions of most simple aliphatic amines have a pKa of about 10 or 11. Now, since $\ce{N}$ is less electronegative than $\ce{O}$, it's lone pair is more readily available than that of $\ce{OH-}$. Below is a table of relative nucleophilic strength. What do you call molecules with this property? this is about to help me on my orgo exam yesss. Why does silver oxide form a coordination complex when treated with ammonia? Co-solvents such as methylene chloride or THF are needed, since pure DMSO freezes at 18. This page titled Acidity of Substituted Phenols is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by William Reusch. x}OHQ%Be&RNW`okn%B.A1XI:b]"(7373{@](mzy(;>7PA+Xf$vlqd}] UxiO:bM1Wg>q[ You can, however, force two lone pairs into close proximity. 745 Acidity of Substituted Phenols - Chemistry LibreTexts endstream Most base reagents are alkoxide salts, amines or amide salts. Think about it for a second.good nucleophiles (as shown above) can have a negative charge and will almost always have a lone pair. We see this in calculations and experiments that show nucleophilicity decreases as you get closer to fluorine on the periodic table (C > N > O > F). The significance of all these acid-base relationships to practical organic chemistry lies in the need for organic bases of varying strength, as reagents tailored to the requirements of specific reactions. We normally think of amines as bases, but it must be remembered that 1 and 2-amines are also very weak acids (ammonia has a pKa = 34). Three examples of these DMSO oxidations are given in the following diagram. The following compounds have similar pKa values because the activating groups are not bonded directly to OH: CH3C(=O)CH2OH, PhCH2OH, and CH3CH2OH. Two additional points should be made concerning activating groups. This greatly decreases the basicity of the lone pair electrons on the nitrogen in an amide. This phenolic acidity is further enhanced by electron-withdrawing substituents ortho and para to the hydroxyl group, as displayed in the following diagram. The alcohol cyclohexanol is shown for . The region and polygon don't match. Great nucleophile, really poor base. { Acidity_of_Phenols : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Acidity_of_Substituted_Phenols : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Physical_Properties_of_Phenol : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()" }, { Properties_of_Phenols : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Reactivity_of_Phenols : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", Synthesis_of_Phenols : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()" }, [ "article:topic-category", "authorname:wreusch", "showtoc:no", "license:ccbyncsa", "licenseversion:40" ], https://chem.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fchem.libretexts.org%2FBookshelves%2FOrganic_Chemistry%2FSupplemental_Modules_(Organic_Chemistry)%2FPhenols%2FProperties_of_Phenols%2FAcidity_of_Substituted_Phenols, \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}}}\) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\), status page at https://status.libretexts.org. Other names are noted in the table above. PEG1334172-76-7 Biotin-PEG7-NH2 ,PEG1334172-76-7 Biotin-PEG7-NH2 << /Length 5 0 R /Filter /FlateDecode >> 14 years and about 60,000 students later, we are still helping students to learn organic chemistry one reaction at a time at https://www.aceorganicchem.com, thank you so much for the informations Legal. Adding these two chemical equations together yields the equation for the autoionization for water: \[\cancel{\ce{RNH3+}(aq)}+\ce{H2O}(l)+\cancel{\ce{RNH2}(aq)}+\ce{H2O}(l)\ce{H3O+}(aq)+\cancel{\ce{RNH2}(aq)}+\ce{OH-}(aq)+\cancel{\ce{RNH3+}(aq)}\], \[\ce{2H2O}(l)\ce{H3O+}(aq)+\ce{OH-}(aq)\]. How is that? _ The prefix thia denotes replacement of a carbon atom in a chain or ring by sulfur, although a single ether-like sulfur is usually named as a sulfide. For more information on this and other topics of organic chemistry interest, please visit organic chemistry, Dr. Mike Pa got a bachelors degree in chemistry from Binghamton University, a masters degree in organic chemistry from the University of Arizona and a PhD in bio-organic chemistry from the University of Arizona. #4 Importance - within a functional group category, use substituent effects to compare acids. ERROR: CREATE MATERIALIZED VIEW WITH DATA cannot be executed from a function, Bulk update symbol size units from mm to map units in rule-based symbology, Is there a solutiuon to add special characters from software and how to do it. SH NH2 Compound A Compound B Options: less acidic atom principle induction principle more acidic resonance principle orbital principle Even without reference to pkas, we can predict that compound A is than compound B by applying the Since alcohols are much stronger acids than amines, their conjugate bases are weaker than amine bases, and fill the gap in base strength between amines and amide salts. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. I am not so pleased with this argument. It is common to compare basicity's of amines by using the Ka's of their conjugate acids, which is the corresponding ammonium ion. [ /ICCBased 9 0 R ] You will hear a lot about bulky bases, which are nucleophilic but too darn big to be a nucleophile and can only be a base. Thanks for contributing an answer to Chemistry Stack Exchange! "Scan and rank" sounds simple, but it conceals several difficulties that are elaborated below. Legal. The addition of substituents onto the aromatic ring can can make arylamines more or less basic. Question: a) the stronger acid or SH NH2 or b) the stronger base NH2 Cl c) the greater bond angle CH3 or CH3 trans-1,2-dimethylcyclohexane d) the more stable isomer or trans-1,3-dimethylcyclohexane e) the higher boiling point CH3 f) the tertiary amine CH3 or NH2 g) the greater solubility in water h) the more stable base i) the stronger acid or b) p-Ethylaniline, p-Bromoaniline, p-aminobenzonitrile Amine are basic and easily react with the hydrogen of acids which are electron poor as seen below. Bases accept protons, with a negative charge or lone pair. MathJax reference. stream Fortunately, the Ka and Kb values for amines are directly related. sulfones) electrons. A limit involving the quotient of two sums, Redoing the align environment with a specific formatting. oyuuTDIh2?hhn:7Hkh7id.7KVi~*-^C^p The reasons for this different behavior are not hard to identify. Organic chemistry is all about reactions. The following chart shows how each group of atoms activates an OH acid (pKa values range from 16 to -2): CH3 is considered a spectator group wherever it appears in these molecules. You shouldn't compare the basicity of Hydrazine as a molecule. Remember, smaller nucleophiles can fit into more places, therefore will be able to react at more places and will necessarily be more nucleophilic. View the full answer. From previous discussion it should be clear that the basicity of these nitrogens is correspondingly reduced. The SS single bond is nearly twice as strong as the OO bond in peroxides, and the OH bond is more than 25 kcal/mole stronger than an SH bond. I- is the best example of this. Calculate its mass density. These effects are enhanced when 1) the substituent is located closer to the acidic group, and 2) there are multiple substituents. The common base sodium hydroxide is not soluble in many organic solvents, and is therefore not widely used as a reagent in organic reactions. Finally, oxidation of sulfides with hydrogen peroxide (or peracids) leads first to sulfoxides and then to sulfones. Euler: A baby on his lap, a cat on his back thats how he wrote his immortal works (origin?). endobj This destabilizes the unprotonated form. My concern is that you understand what is meant by "all things being equal." Mild oxidation of disufides with chlorine gives alkylsulfenyl chlorides, but more vigorous oxidation forms sulfonic acids (2nd example). Pyridine is commonly used as an acid scavenger in reactions that produce mineral acid co-products. Substituents which are electron-withdrawing (-Cl, -CF3, -CN, -NO2) decrease the electron density in the aromatic ring and on the amine making the arylamine less basic. The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. This has a lot to do with sterics. Describe the categorization of these amino acids, and which amino acids that belong to each group. The shifting electron density of aniline, p-nitroaniline, and p-methoxyaniline are seen in their relative electrostatic potential maps. The reaction is operationally easy: a DMSO solution of the alcohol is treated with one of several electrophilic dehydrating reagents (E). NH4NO2(s)2H2O(g)+N2(g). It was proposed that resonance delocalization of an oxygen non-bonded electron pair into the pi-electron system of the aromatic ring was responsible for this substituent effect. Remember that, relative to hydrogen, alkyl groups are electron releasing, and that the presence of an electronreleasing group stabilizes ions carrying a positive charge. Amines react with water to establish an equilibrium where a proton is transferred to the amine to produce an ammonium salt and the hydroxide ion, as shown in the following general equation: \[RNH2_{(aq)}+H_2O_{(l)} \rightleftharpoons RNH3^+_{(aq)}+OH^_{(aq)} \label{16.5.4}\]. The strong bases are listed at the bottom right of the table and get weaker as we move to the top of the table. size and polarizable effects are contracdictory,if size of the atom is larger more polarizablity is increases, therefore larger the size nucleophilicity increases. The chemical behavior of thiols and sulfides contrasts with that of alcohols and ethers in some important ways. Ranking proceeds more quickly if you rank the OH and NH acids separately, and then compare the top candidates in each category. In particular, the nitro group of para-nitroaniline allows for an additional resonance form to be drawn, which further stabilizes the lone pair electrons from the nitrogen, making the substituted arylamine less basic than aniline. discuss, in terms of inductive and resonance effects, why a given arylamine is more or less basic than aniline. Supporting evidence that the phenolate negative charge is delocalized on the ortho and para carbons of the benzene ring comes from the influence of electron-withdrawing substituents at those sites. 10 0 obj Simply put, you must scan the molecule for acidic functional groups, and then rank the reactivity of these groups. I am not a huge fam of memorizing charts, but this might be a good one to know pretty well. Organic Chemistry made easy. Mention 5 of these. Just as the acid strength of a carboxylic acid can be measured by defining an acidity constant K a (Section 2-8), the base strength of an amine can be measured by defining an analogous basicity constant K b. The larger the value of K b and the smaller the value of pK b, the more favorable the proton-transfer equilibrium and the stronger the . 3. NH NH Compound A Compound B Options: orbital principle less acidic resonance principle induction principle more acidic atom. This is an awesome problem of Organic Acid-Base Rea . Strong nucleophilesthis is why molecules react. The ONLY convenient method for identifying a functional group is to already know some. This reaction may be used to prepare pure nitrogen. Table of Acid and Base Strength - University of Washington The increasing s-character brings it closer to the nitrogen nucleus, reducing its tendency to bond to a proton compared to sp3 hybridized nitrogens. Make certain that you can define, and use in context, the key term below. The nucleophilic site of the nucleophile is the region of a molecule that is reactive and has the electron density. Can I tell police to wait and call a lawyer when served with a search warrant? endobj arrange a given series of arylamines in order of increasing or decreasing basicity. ;zP"$ O&o_b$AS(A\Be]/gWU_A(Pbpg/X-^O&cGA=+}"$!yFT9TQpzkxnW $A%UCV|^s!0nHd;qr![FiETZ>>2f>j;V2~3;TwY5{Z-_B:~Y(UF?wF4 endstream PEG1334172-76-7 Biotin-PEG7-NH2 - Indeed, the S=O double bonds do not consist of the customary & -orbitals found in carbon double bonds. The only neutral acids that are stronger than ROH2+ are H2SO4 and certain other RSO3H. -ve charge easily, hence NH2 is more acidic than OH. Strong nucleophiles are VERY important throughout organic chemistry, but will be especially important when trying to determine the products of elimination and substitution (SN1 vs SN2) reactions. Find pI of His. Although equivalent oxonium salts of ethers are known, they are only prepared under extreme conditions, and are exceptionally reactive. I'm saying that the presence of a positive charge near the electrons will try to reduce its intensity and make it somewhat stable. How much does it weigh? 4Ix#{zwAj}Q=8m The IUPAC name of (CH3)3CSH is 2-methyl-2-propanethiol, commonly called tert-butyl mercaptan. What group on the amino acid give the molecule its characteristics and, when in polymers, the whole protein its shape and function? Michael David Wiley Ph.D. in Organic Chemistry, University of Washington (Graduated 1969) Author has 188 answers and 231.1K answer views 4 y Related Is NH2- a stronger base than OH-? In each case the heterocyclic nitrogen is sp2 hybridized. This destabilizes the unprotonated form. A certain spring has a force constant kkk. The nucleophilic site of the nucleophile is the region of a molecule that is reactive and has the electron density. As noted in our earlier treatment of electrophilic aromatic substitution reactions, an oxygen substituent enhances the reactivity of the ring and favors electrophile attack at ortho and para sites. For the second point you made, more number of nucleophilic sites would mean more chances of attack of an $H^+$, which adds to the basicity of Hydrazine. You'll get a detailed solution from a subject matter expert that helps you learn core concepts. The remaining steps are eliminations, similar in nature to those proposed for other alcohol oxidations. Ammonia is more basic than hydrazine if you look at the neighbors you will see $NH_3$, and $NH_2-NH_2$ where Ammonia has hydrogen as third neighbor where hydrazine have N as neighbors which gives more strong - I effect, after protonation. As a third row element, sulfur has five empty 3d-orbitals that may be used for p-d bonding in a fashion similar to p-p () bonding. I'm just saying that the probability of attack, and did not mean that it decreases it's $pK_b$ value. Is it a bug? c) p-Methoxyaniline, p-methylaniline, p-(trifluoromethyl)aniline. If you restrict your formulas to valence shell electron octets, most of the higher oxidation states will have formal charge separation, as in equation 2 above. Use MathJax to format equations. We see some representative sulfur oxidations in the following examples. Aniline is substantially less basic than methylamine, as is evident by looking at the pKa values for their respective ammonium conjugate acids (remember that the lower the pKa of the conjugate acid, the weaker the base). The alkoxides are stronger bases that are often used in the corresponding alcohol as solvent, or for greater reactivity in DMSO. It is noteworthy that the influence of a nitro substituent is over ten times stronger in the para-location than it is meta, despite the fact that the latter position is closer to the hydroxyl group. To clarify the first part, I am not saying that the electrons will jump to the protonated nitrogen. Why is NH2 (-) more basic than (H-)? : r/chemhelp - Reddit Thiolate conjugate bases are easily formed, and have proven to be excellent nucleophiles in SN2 reactions of alkyl halides and tosylates. XcPm{P>CAKHi3h"Pa>Kx3_Gi_aKdD^E5I $8:HME1f\:fg*&4,ZTkmLcGD6b"o7Z' &S. Which is the stronger acid - R-OH or R-SH? - Quora Acid with values less than one are considered weak. In the following table, pKa again refers to the conjugate acid of the . The poor nucleophiles is more favor to Sn1 reaction than Sn2 reaction. Yes, O is more electronegative than S, and forms a more polar bond with H. However, if it's easier for a base to extract a proton from the hydroxyl than the thiol, that would imply that the hydroxyl proton is more acidic than the thiol proton. Asking for help, clarification, or responding to other answers. The electronwithdrawing (i.e., deactivating) substituents decrease the stability of a positively charged arylammonium ion. a) p-Chloroaniline, methyl p-aminobenzoate, p-nitroaniline {$"F'X&/Zl*nq.- #->2-Ti(} FYDiMZyYll!/T]Mx(-eZ%^YyOa|_;}D&T IDHOB(=QO'w The effect of delocalization can be seen when viewing the electrostatic potential maps of aniline an methyl amine. Generally, polarizability increases as you travel down a column of the periodic table (I > Br > Cl > F). The equilibrium constant for this reaction is the base ionization constant (Kb), also called the base dissociation constant: \[K_b=\dfrac{[RNH3^+][OH^]}{[NH2]} \label{16.5.5}\]. Nucleophilicity of Sulfur Compounds The formulas written here neutralize this charge separation by double bonding that expands the valence octet of sulfur. Just as the acid strength of a carboxylic acid can be measured by defining an acidity constant Ka (Section 2-8), the base strength of an amine can be measured by defining an analogous basicity constant Kb. Essential amino acids are those amino acids that must be obtained from the proteins in the diet. The lone pair electrons makes the nitrogen in amines electron dense, which is represents by a red color in the electrostatic potential map present below left. rev2023.3.3.43278. The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. [With free chemistry study guide]. The Protonation of Acetamide and Thioacetamide in Superacidic Enantiomeric sulfoxides are stable and may be isolated. So, lets look at what makes strong nucleophiles: There are generally three factors to remember when discussing how nucleophilic a reactant is: 1) Size Generally (but not always)the more linear and/or smaller the nucleophile, the more nucleophilic it will be. If you do not recall pKa values for all of the acidic groups, a few general principles can guide you. Has 90% of ice around Antarctica disappeared in less than a decade? The pKa values of common OH and NH acids span wide ranges and their ranges overlap. This is because it can react at more sites and will not be sterically hindered if it is smaller or linear. We didnt consider the M effect of NH2 here because its not possible to donate right @MathewMahindaratne ? This isn't the case. This means that O and N must have the same formal charge (item #1) and must be bonded to the same activating group (item #2). After completing this section, you should be able to. We really need to know what is nucleophilic and what is not so that we can determine what is going to react at the electrophilic site. Nucleophilicity of Sulfur Compounds is shared under a CC BY-NC-ND 3.0 license and was authored, remixed, and/or curated by William Reusch. Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University), Prof. Steven Farmer (Sonoma State University), William Reusch, Professor Emeritus (Michigan State U. The conjugate bases of simple alcohols are not stabilized by charge delocalization, so the acidity of these compounds is similar to that of water. xKo@|9R{&CV{:%r;_PQ0flf7|;0E"$w] g(o6Mf=aVZ_v7b6QD9$0 5TFN>0d8K4[:KsW `0p'a`b>lxvlU7a8\!E^-\:,U This is expected, because the -NH2 group is more electronegative than -H or -CH3. Extraction is often employed in organic chemistry to purify compounds. While the electron density of aniline's nitrogen is delocalized in the aromatic ring making it less basic. stream The formal charge rule applies even more strongly to NH acids. The difference in pKa between H3O+ and H2O is 18 units, while the difference in pKa between NH4+ and NH3 is a gigantic 26 units. At pH 7,4 the surrounding will be more acidic than Histidine pI.It takes up a hydrogen atom at the R-group. Abel already answered that at one time only one $\ce{-NH_2}$ takes part when we determine basicity and the second $\ce{-NH_2}$ plays no role. Scan a molecule for known acidic functional groups. How do you determine the acidity of amines? $$\ce{H2N-NH2 + H3O+ <=> H3N^+-NH2 + H2O} \tag2$$. First, the groups exert a similar effect on NH acids (and the activating sequence is the same: RSO2 > RC=O > Ph). Furthermore additional nitro groups have an additive influence if they are positioned in ortho or para locations. Making statements based on opinion; back them up with references or personal experience. The aqueous layer is then treated with a base (NaOH) to regenerate the amine and NaCl. This is expected, because the -NH 2 group is more electronegative than -H or -CH 3. % The very low basicity of pyrrole reflects the exceptional delocalization of the nitrogen electron pair associated with its incorporation in an aromatic ring. The prefix thio denotes replacement of a functional oxygen by sulfur. How can I find out which sectors are used by files on NTFS? Bonding of sulfur to the alcohol oxygen atom then follows. Remarkably, sulfoxides (equation # 2), sulfinate salts (# 3) and sulfite anion (# 4) also alkylate on sulfur, despite the partial negative formal charge on oxygen and partial positive charge on sulfur. Note that the arylammonium ion derived from aniline, PhNH3+, is commonly referred to as the anilinium ion. 4 0 obj It should be noted that the first four examples have the same order and degree of increased acidity as they exhibited decreased basicity in the previous table. Sn1 proceed faster in more polar solvent compare to Sn2. Like ammonia, most amines are Brnsted-Lowry and Lewis bases, but their base strength can be changed enormously by substituents. Which of the following will be more basic, hydrazine $\ce{H2N-NH2}$ or ammonia $\ce{NH3}$? Finally, the two amide bases see widespread use in generating enolate bases from carbonyl compounds and other weak carbon acids. Ammonia is more basic than hydrazine, by about one order of magnitude. Hnig's base is relatively non-nucleophilic (due to steric hindrance), and is often used as the base in E2 elimination reactions conducted in non-polar solvents. Strong Nucleophiles [with study guide & chart] - Organic chemistry help Aromatic herterocyclic amines (such as pyrimidine, pyridine, imidazole, pyrrole) are significantly weaker bases as a consequence of three factors. NH4NO2(s)2H2O(g)+N2(g)NH_4NO_2(s) \longrightarrow 2H_2O(g) + N_2(g) Order of basicity for arylamines and ammonia in gas phase, Time arrow with "current position" evolving with overlay number, Follow Up: struct sockaddr storage initialization by network format-string. For example, C2H5SC3H7 is ethyl propyl sulfide and C2H5SCH2SC3H7 may be named 3,5-dithiaoctane. This is because more electronegative atoms will hold electron density closer, and therefore will be less likely to let that electron density participate in a reaction. In $\ce{H3N+-NH2}$, although the lone pair cannot be accommodated, but the positive charge present on its sides , to an extent, should neutralize the intensity of the lone pair, making it somewhat stable. The last two compounds (shaded blue) show the influence of adjacent sulfonyl and carbonyl groups on N-H acidity. So instead, $\ce{-NH2}$ will pull electrons from it making it unstable. inorganic chemistry - Which is more basic, hydrazine or ammonia Strong nucleophiles are VERY important throughout organic chemistry, but will be especially important when trying to determine the products of elimination and substitution ( SN1 . This is because when the proton leaves the compound, the negative charge on RSH is dispersed more on it as compared to ROH (due to larger size of S than O). 7) Gly Gly . The keyword is "proton sponge". What is a non-essential amino acid? Substitution of the hydroxyl hydrogen atom is even more facile with phenols, which are roughly a million times more acidic than equivalent alcohols.

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