Which of the Following Can Serve as a Nucleophile?

Chemical species that donates an electron pair

In chemistry, a nucleophile is a chemical species that forms bonds with electrophiles by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond tin can act every bit nucleophiles. Because nucleophiles donate electrons, they are Lewis bases.

Nucleophilic describes the affinity of a nucleophile to bond with positively charged atomic nuclei. Nucleophilicity, sometimes referred to every bit nucleophile strength, refers to a substance's nucleophilic character and is often used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis. Nucleophiles may accept part in nucleophilic substitution, whereby a nucleophile becomes attracted to a total or partial positive accuse, and nucleophilic addition. Nucleophilicity is closely related to basicity.

History [edit]

The terms nucleophile and electrophile were introduced by Christopher Kelk Ingold in 1933,^[one] replacing the terms anionoid and cationoid proposed before by A. J. Lapworth in 1925.^[ii] The word nucleophile is derived from nucleus and the Greek word φιλος, philos, meaning friend.

Backdrop [edit]

In general, in a group across the periodic table, the more basic the ion (the college the pK_a of the conjugate acrid) the more reactive it is as a nucleophile. Inside a series of nucleophiles with the same attacking element (e.thousand. oxygen), the lodge of nucleophilicity will follow basicity. Sulfur is in full general a better nucleophile than oxygen.

Nucleophilicity [edit]

Many schemes attempting to quantify relative nucleophilic strength have been devised. The following empirical information accept been obtained by measuring reaction rates for many reactions involving many nucleophiles and electrophiles. Nucleophiles displaying the so-chosen alpha effect are usually omitted in this blazon of handling.

Boyfriend–Scott equation [edit]

The first such attempt is constitute in the Boyfriend–Scott equation^{[3] [iv]} derived in 1953:

${\displaystyle \log _{10}\left({\frac {k}{k_{0}}}\right)=sn}$

This free-energy relationship relates the pseudo showtime society reaction rate abiding (in water at 25 °C), k, of a reaction, normalized to the reaction charge per unit, m ₀, of a standard reaction with h2o every bit the nucleophile, to a nucleophilic abiding n for a given nucleophile and a substrate constant s that depends on the sensitivity of a substrate to nucleophilic attack (divers as i for methyl bromide).

This handling results in the following values for typical nucleophilic anions: acetate 2.seven, chloride iii.0, azide 4.0, hydroxide 4.two, aniline 4.5, iodide 5.0, and thiosulfate 6.4. Typical substrate constants are 0.66 for ethyl tosylate, 0.77 for β-propiolactone, 1.00 for ii,three-epoxypropanol, 0.87 for benzyl chloride, and 1.43 for benzoyl chloride.

The equation predicts that, in a nucleophilic displacement on benzyl chloride, the azide anion reacts 3000 times faster than water.

Ritchie equation [edit]

The Ritchie equation, derived in 1972, is another free-energy relationship:^{[v] [6] [vii]}

${\displaystyle \log _{10}\left({\frac {m}{k_{0}}}\right)=North^{+}}$

where North ⁺ is the nucleophile dependent parameter and thou ₀ the reaction charge per unit constant for water. In this equation, a substrate-dependent parameter like s in the Swain–Scott equation is absent. The equation states that two nucleophiles react with the aforementioned relative reactivity regardless of the nature of the electrophile, which is in violation of the reactivity–selectivity principle. For this reason, this equation is besides called the constant selectivity relationship.

In the original publication the data were obtained by reactions of selected nucleophiles with selected electrophilic carbocations such equally tropylium or diazonium cations:

or (non displayed) ions based on malachite green. Many other reaction types take since been described.

Typical Ritchie N⁺ values (in methanol) are: 0.5 for methanol, 5.9 for the cyanide anion, 7.v for the methoxide anion, 8.5 for the azide anion, and 10.7 for the thiophenol anion. The values for the relative cation reactivities are −0.iv for the malachite dark-green cation, +2.6 for the benzenediazonium cation, and +4.5 for the tropylium cation.

Mayr–Patz equation [edit]

In the Mayr–Patz equation (1994):^[viii]

${\displaystyle \log(k)=south(N+E)}$

The second lodge reaction rate constant k at 20 °C for a reaction is related to a nucleophilicity parameter North, an electrophilicity parameter E, and a nucleophile-dependent slope parameter south. The constant s is defined equally 1 with 2-methyl-1-pentene as the nucleophile.

Many of the constants have been derived from reaction of and so-called benzhydrylium ions as the electrophiles:^[9]

and a various collection of π-nucleophiles:

.

Typical E values are +vi.2 for R = chlorine, +5.90 for R = hydrogen, 0 for R = methoxy and −7.02 for R = dimethylamine.

Typical North values with south in parenthesis are −4.47 (1.32) for electrophilic effluvious substitution to toluene (1), −0.41 (ane.12) for electrophilic improver to i-phenyl-two-propene (2), and 0.96 (i) for addition to 2-methyl-1-pentene (3), −0.13 (one.21) for reaction with triphenylallylsilane (4), 3.61 (1.11) for reaction with ii-methylfuran (v), +7.48 (0.89) for reaction with isobutenyltributylstannane (vi) and +13.36 (0.81) for reaction with the enamine 7.^[x]

The range of organic reactions too include SN2 reactions:^[eleven]

With East = −9.15 for the S-methyldibenzothiophenium ion, typical nucleophile values Northward (s) are 15.63 (0.64) for piperidine, 10.49 (0.68) for methoxide, and 5.20 (0.89) for water. In curt, nucleophilicities towards sp₂ or sp₃ centers follow the same blueprint.

Unified equation [edit]

In an effort to unify the above described equations the Mayr equation is rewritten as:^[eleven]

${\displaystyle \log(thousand)=s_{E}s_{N}(N+E)}$

with s_E the electrophile-dependent slope parameter and s_{Due north} the nucleophile-dependent slope parameter. This equation can be rewritten in several ways:

• with s_E = 1 for carbocations this equation is equal to the original Mayr–Patz equation of 1994,
• with due south_N = 0.6 for most due north nucleophiles the equation becomes

${\displaystyle \log(thou)=0.6s_{East}Northward+0.6s_{Due east}East}$

or the original Scott–Fellow equation written equally:

${\displaystyle \log(grand)=\log(k_{0})+s_{Eastward}Northward}$

• with s_E = one for carbocations and due south_N = 0.6 the equation becomes:

${\displaystyle \log(k)=0.6N+0.6E}$

or the original Ritchie equation written every bit:

${\displaystyle \log(k)-\log(k_{0})=N^{+}}$

Types [edit]

Examples of nucleophiles are anions such equally Cl⁻, or a compound with a alone pair of electrons such as NH₃ (ammonia), PR₃.

In the case below, the oxygen of the hydroxide ion donates an electron pair to course a new chemical bond with the carbon at the terminate of the bromopropane molecule. The bail between the carbon and the bromine then undergoes heterolytic fission, with the bromine atom taking the donated electron and becoming the bromide ion (Br⁻), considering a S_North2 reaction occurs by backside attack. This means that the hydroxide ion attacks the carbon atom from the other side, exactly contrary the bromine ion. Because of this behind attack, S_Nii reactions upshot in a inversion of the configuration of the electrophile. If the electrophile is chiral, it typically maintains its chirality, though the S_N2 production's absolute configuration is flipped as compared to that of the original electrophile.

An ambident nucleophile is ane that can attack from two or more than places, resulting in two or more products. For case, the thiocyanate ion (SCN⁻) may attack from either the sulfur or the nitrogen. For this reason, the S_Nii reaction of an alkyl halide with SCN⁻ often leads to a mixture of an alkyl thiocyanate (R-SCN) and an alkyl isothiocyanate (R-NCS). Similar considerations apply in the Kolbe nitrile synthesis.

Halogens [edit]

While the halogens aren't nucleophilic in their diatomic class (e.one thousand. I₂ is not a nucleophile), their anions are proficient nucleophiles. In polar, protic solvents, F⁻ is the weakest nucleophile, and I⁻ the strongest; this order is reversed in polar, aprotic solvents.^[12]

Carbon [edit]

Carbon nucleophiles are often organometallic reagents such as those found in the Grignard reaction, Blaise reaction, Reformatsky reaction, and Barbier reaction or reactions involving organolithium reagents and acetylides. These reagents are often used to perform nucleophilic additions.

Enols are also carbon nucleophiles. The formation of an enol is catalyzed past acrid or base. Enols are ambident nucleophiles, just, in full general, nucleophilic at the alpha carbon atom. Enols are normally used in condensation reactions, including the Claisen condensation and the aldol condensation reactions.

Oxygen [edit]

Examples of oxygen nucleophiles are water (H₂O), hydroxide anion, alcohols, alkoxide anions, hydrogen peroxide, and carboxylate anions. Nucleophilic attack does not have identify during intermolecular hydrogen bonding.

Sulfur [edit]

Of sulfur nucleophiles, hydrogen sulfide and its salts, thiols (RSH), thiolate anions (RS⁻), anions of thiolcarboxylic acids (RC(O)-Southward⁻), and anions of dithiocarbonates (RO-C(S)-Due south⁻) and dithiocarbamates (R_twoNorth-C(S)-S⁻) are used near frequently.

In general, sulfur is very nucleophilic considering of its big size, which makes it readily polarizable, and its solitary pairs of electrons are readily accessible.

Nitrogen [edit]

Nitrogen nucleophiles include ammonia, azide, amines, nitrites, hydroxylamine, hydrazine, carbazide, phenylhydrazine, semicarbazide, and amide.

Metal centers [edit]

Although metal centers (due east.m., Li⁺, Zn²⁺, Sc³⁺, etc.) are most commonly cationic and electrophilic (Lewis acidic) in nature, certain metal centers (particularly ones in a low oxidation state and/or conveying a negative charge) are amidst the strongest recorded nucleophiles and are sometimes referred to every bit "supernucleophiles." For instance, using methyl iodide as the reference electrophile, Ph_threeSn^– is about 10000 more nucleophilic than I^–, while the Co(I) form of vitamin B₁₂ (vitamin B_12s) is near 10⁷ times more than nucleophilic.^[xiii] Other supernucleophilic metallic centers include low oxidation state carbonyl metalate anions (eastward.g., CpFe(CO)₂ ^–).^[xiv]

Encounter besides [edit]

• Electrophile
• Lewis acids and bases
• Nucleophilic brainchild
• Add-on to pi ligands

References [edit]

1. ^ Ingold, C. K. (1933). "266. Significance of tautomerism and of the reactions of aromatic compounds in the electronic theory of organic reactions". Journal of the Chemical Club (Resumed): 1120. doi:10.1039/jr9330001120.
2. ^ Lapworth, A. (1925). "Replaceability of Halogen Atoms past Hydrogen Atoms". Nature. 115: 625.
3. ^ Quantitative Correlation of Relative Rates. Comparison of Hydroxide Ion with Other Nucleophilic Reagents toward Alkyl Halides, Esters, Epoxides and Acyl Halides C. Gardner Swain, Carleton B. Scott J. Am. Chem. Soc.; 1953; 75(1); 141-147. Abstract
4. ^ "Swain–Scott equation". Aureate Book. IUPAC. February 24, 2014.
5. ^ Gold Volume definition (Ritchie) Link ^{[ permanent dead link ]}
6. ^ Nucleophilic reactivities toward cations Calvin D. Ritchie Acc. Chem. Res.; 1972; 5(10); 348-354. Abstract
7. ^ Cation–anion combination reactions. 13. Correlation of the reactions of nucleophiles with esters Calvin D. Ritchie J. Am. Chem. Soc.; 1975; 97(v); 1170–1179. Abstruse
8. ^ Mayr, Herbert; Patz, Matthias (1994). "Scales of Nucleophilicity and Electrophilicity: A System for Ordering Polar Organic and Organometallic Reactions". Angewandte Chemie International Edition in English. 33 (9): 938. doi:10.1002/anie.199409381.
9. ^ Mayr, Herbert; Bug, Thorsten; Gotta, Matthias F; Hering, Nicole; Irrgang, Bernhard; Janker, Brigitte; Kempf, Bernhard; Loos, Robert; Ofial, Armin R; Remennikov, Grigoriy; Schimmel, Holger (2001). "Reference Scales for the Characterization of Cationic Electrophiles and Neutral Nucleophiles". Periodical of the American Chemical Society. 123 (39): 9500–12. doi:10.1021/ja010890y. PMID 11572670. S2CID 8392147.
10. ^ An cyberspace database for reactivity parameters maintained past the Mayr group is available at http://world wide web.cup.uni-muenchen.de/oc/mayr/
11. ^ ^{a b} Phan, Thanh Binh; Breugst, Martin; Mayr, Herbert (2006). "Towards a General Scale of Nucleophilicity?". Angewandte Chemie International Edition. 45 (23): 3869–74. CiteSeerX10.ane.1.617.3287. doi:10.1002/anie.200600542. PMID 16646102.
12. ^ Chem 2401 Supplementary Notes. Thompson, Alison and Pincock, James, Dalhousie University Chemical science Department
13. ^ Schrauzer, G. N.; Deutsch, E.; Windgassen, R. J. (April 1968). "The nucleophilicity of vitamin B(sub 12s)". Journal of the American Chemic Society. 90 (9): 2441–2442. doi:10.1021/ja01011a054. ISSN 0002-7863. PMID 5642073.
14. ^ Dessy, Raymond E.; Pohl, Rudolph L.; King, R. Bruce (Nov 1966). "Organometallic Electrochemistry. Seven. 1 The Nucleophilicities of Metal and Metalloidal Anions Derived from Metals of Groups Iv, V, VI, 7, and Viii". Journal of the American Chemical Order. 88 (22): 5121–5124. doi:10.1021/ja00974a015. ISSN 0002-7863.

jeffersonmandiess77.blogspot.com

Source: https://en.wikipedia.org/wiki/Nucleophile

Share this post