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Topic: Nucleophilic substitution


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  nucleophilic aromatic substitution nucleophilic aromatic substitution   (Site not responding. Last check: 2007-11-03)
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nucleophilic-aromatic-substitution.wow-words.com   (487 words)

  
 Nucleophilic aromatic substitution - Wikipedia, the free encyclopedia
A nucleophilic substitution is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide on an aromatic ring.
Since the nitro group is a deactivator towards nucleophilic substitution, and a meta director, they allow the benzene carbon to which they are bonded to have a negative charge.
The nucleophilic substitution reactions in organic chemistry are nucleophilic aliphatic substitution including SN1 reactions, SN2 reactions and SNi reactions, nucleophilic aromatic substitution and nucleophilic acyl substitution.
en.wikipedia.org /wiki/Nucleophilic_aromatic_substitution   (483 words)

  
 Nucleophilic Substitution
These reactions are known as Nucleophilic Substitution Reactions, substitution reactions because one atom or group has been substituted for another, and nucleophilic because the substituting atom or group has supplied the electrons for the new bond.
There is roughly a half bond between the nucleophile and the carbon and a half bond between the carbon and the halogen.
Notice that the nucleophile is bringing its bond-forming electrons into the transition state on the side of the carbon opposite to the position of the leaving group.
chemistry2.csudh.edu /rpendarvis/SN2.html   (1647 words)

  
 Nucleophilic Substitution of Alkyl Halides
Nucleophilic substitution is a reaction in which an incoming nucleophile substitutues (replaces) an outgoing leaving group.
Nucleophiles have lone pairs of electrons and may carry a negative charge.
The main factors that govern the pathway for this reaction are the steric hinderence of the alkyl halide and the stability of the carbocation intermediate.
web.mala.bc.ca /patrick/nucleophilic_substitution_of_alk.htm   (648 words)

  
 Nucleophilic Substitution Reactions
Nucleophilic substitution reactions are an important class of reactions that allow the interconversion of functional groups, for example R-OH ®;
Nucleophilic substitution will be explored in much more detail in chapter 8.
In the reactions of alcohols with HX, the reactivity trend of HI > HBr > HCl > HF is not due to the nucleophilicity of the halide ion but the acidity of HX which is involved in generating the leaving group prior to the rate determining step.
www.mhhe.com /physsci/chemistry/carey/student/olc/ch04nucle.html   (1065 words)

  
 Sn2
The lack of any correlation between the concentration or the identity of the nucleophile and the rate of substitution led chemists to postulate a 2-step process in which the first step involved ionization of the bond between the reaction center and the leaving group.
In the second transition state the bond between the nucleophile and the reaction center is partially formed; the charge on the carbon atom is diminishing from +1 towards 0, while the charge on the hydroxide ion is changing from -1 towards 0.
In reaction 4, the carboxylate anion is thought to act like an internal nucleophile, assisting the departure of the leaving group by coordinating to the back side of the C-Br bond and blocking access of the nucleophile to that side of the molecule.
www.usm.maine.edu /~newton/Chy251_253/Lectures/Sn1/Sn1.html   (2061 words)

  
 Alkyl Halide Reactivity
2 mechanism are inversion at the alpha-carbon, increased reactivity with increasing nucleophilicity of the nucleophilic reagent and steric hindrance to rear-side bonding, especially in tertiary and neopentyl halides.
Second, since nucleophiles only participate in the fast second step, their relative molar concentrations rather than their nucleophilicities should be the primary product-determining factor.
For many combinations of alkyl halides and nucleophiles, elimination reactions may compete with substitution, or even be the predominant reaction path.
www.cem.msu.edu /~reusch/VirtualText/alhalrx2.htm   (1186 words)

  
 Nucleophilic Aromatic Substitution
Nucleophilic conjugate addition A comparison of aliphatic halogenoalkanes and aromatic halides is dealt with in FURTHER COMMENTS.
Nucleophilic substitution of halogenoalkane by hydroxide ion (hydrolysis Nucleophilic Aromatic Substitution: Bimolecular displacement carbanion reactivity orientation.
Aryl halides do not undergo nucleophilic substitution by either When applied to aromatic halides as in the present discussion this mechanism is called S N Ar.
www.ryanborcherding.com /nucleophilic-aromatic-substitution.htm   (279 words)

  
 NUCLEOPHILIC SUBSTITUTION REACTIONS-SN1-REACTIONS-SN2-REACTIONS
Nucleophilic substitution reaction are represented by the symbol "SN".
Such displacement reactions are called nucleophilic substitution reactions.
Therefore, SN is a unimolecular nucleophilic substitution reaction.
www.citycollegiate.com /alkyl_halide2.htm   (255 words)

  
 Organic Chemistry help - Student Doctor Network Forums
The sulfonyl group is attacked by the nucleophilic carbonyl oxygen, which causes the carbonyl carbon to be electron poor.
Likewise, SN reactions are said to be a concerted mechanism, despite cases where the nucleophile must be neutralized with a work-up step (amines substituting for a halide are a great example).
Hence, whether a carbonyl substitution reaction is carried out in acid (making the carbonyl more electrophilic) or base (making the nucleophile more nucleophilic), the number of key steps is still two: (1) formation of the tetrahedral intermediate following attack by the nucleophile and (2) the loss of the leaving group.
forums.studentdoctor.net /showthread.php?t=42044   (2023 words)

  
 Sn2
A leaving group is any atom or polyatomic group that is replaced by a nucleophile during a nucleophilic aliphatic substitution reaction.
In most nucleophilic aliphatic substitution reactions, the value of the equilibrium constant is very large, i.e.
It all depends on your perspective; the reagent that acts as a nucleophile in the forward direction assumes the role of a leaving group in the reverse direction.
www.usm.maine.edu /~newton/Chy251_253/Lectures/Sn2/Sn2.html   (477 words)

  
 Nucleophilic Substitution & Elimination (via CobWeb/3.1 planetlab2.cs.unc.edu)   (Site not responding. Last check: 2007-11-03)
Last time we saw an overview of the nucleophilic substitution mechanisms of alkyl halides.
One outcome of this is that the carbocation intermediate "lives" long enough for a nucleophile to approach it on either face of the molecule.
When the nucleophile is also the solvent, the reaction is called "solvolysis." Solvents like water and alcohols are particularly useful here, because they provide both a nucleophilic pair of electrons on the oxygen atom of the OH group and a fairly polar solvent which helps to stabilize the strongly polar transition state.
chemistry2.csudh.edu.cob-web.org:8888 /rpendarvis/SN1Elim.html   (2034 words)

  
 ORGANIC CHEMISTRY MECHANISMS - HALOGENOALKANES (Haloalkanes, alkyl halides derivatives) nucleophilic substitution with ...
Con-current nucleophilic substitution AND elimination reactions are discussed at the end of the section on the elimination mechanism where things get even more complicated.
Nucleophilic substitution of a halogenoalkane with ammonia or primary aliphatic amine
Compared to nucleophilic substitution, elimination is favoured by using a stronger base like KOH, ethanol as the solvent, rather than water and a tertiary structured halogenoalkane.
www.wpbschoolhouse.btinternet.co.uk /page06/OrgMechs2.htm   (4017 words)

  
 Nucleophilic substitution - Wikipedia, the free encyclopedia
In 1935, Edward D. Hughes and Sir Christopher Ingold studied nucleophilic substitution reactions of alkyl halides and related compounds.
2 occurs where the central carbon atom is easily accessible to the nucleophile.
The Finkelstein reaction is an halide exchange reaction and phosphorus nucleophiles appear in the Perkow reaction and the Michaelis-Arbuzov reaction.
en.wikipedia.org /wiki/Nucleophilic_substitution   (744 words)

  
 CHEM 331, Organic Chemistry I   (Site not responding. Last check: 2007-11-03)
These comments summarize the two substitution mechanisms and the two elimination mechanisms encountered for alkyl halides.
Nucleophiles that are basic, such as OH-, result in competition.
A limited number of nucleophiles, such as, are weakly basic (soft bases) and hence cause only substitution to occur without any elimination.
www.towson.edu /~ryzhkov/handouts/SEhand.html   (1486 words)

  
 C 2131 Nucleophilic Substitution Reactions   (Site not responding. Last check: 2007-11-03)
The most obvious group of compounds to undergo nucleophilic substitution are the alkyl halides.
Remember that a nucleophile is a reagent that donates an unshared electron pair to form a new bond, it is electron rich, it is acting as a Lewis base.
The effectiveness of a nucleophile can be measured and a relative scale of nucleophilicity can be arrived at.
www.mta.ca /~acockshu/c2131sn.html   (1015 words)

  
 C2131 Nucleophilic Acyl Substitution Reactions   (Site not responding. Last check: 2007-11-03)
the nucleophilic acyl substitution reactions have a lot in common with nucleophilic addition reactions to carbonyls.
the major difference between the two reaction types is that the carbonyl group is regenerated in nucleophilic acyl substitution with the loss of a leaving group.
In the first step of each (regardless of the catalysis, this is the first major step), a nucleophile attacks the carbonyl carbon pushing electrons up onto the carbonyl oxygen generating a tetrahedral carbonyladdition intermediate.
www.mta.ca /~acockshu/c2131acylsubst.html   (892 words)

  
 Chapter 8: Nucleophilic Substitution   (Site not responding. Last check: 2007-11-03)
A third possibility, where the nucleophile adds then the leaving group departs can't occur because it would require that the electrophilic C become pentavalent.
the substitution) is often the same regardless of whether it is SN1 or SN2, though they may be differences in regiochemistry and / or stereochemistry (which can provide some evidence as to which mechanistic path is occuring).
This is important since students often want to make use of nucleophilic substitution reactions of vinyl or aryl systems which are not generally effective.
www.chem.ucalgary.ca /courses/351/Carey/Ch08/ch8-1.html   (195 words)

  
 nucleophilic substitution - halogenoalkanes and ammonia
This page gives you the facts and simple, uncluttered mechanisms for the nucleophilic substitution reactions between halogenoalkanes and ammonia to produce primary amines.
If you are interested in further substitution reactions, you will also find a link to a separate page dealing with these.
Ethylamine is a good nucleophile, and goes on to attack unused bromoethane.
www.chemguide.co.uk /mechanisms/nucsub/ammonia.html   (603 words)

  
 Nucleophilic Acyl Substitution   (Site not responding. Last check: 2007-11-03)
Many of the same kinds of nucleophiles that add to aldehyde and ketone carbonyls will attack the carbonyl of an acid (acyl) derivative like an acid chloride, and yield substitution products.
The filled-empty interaction is between the filled p on the nucleophile and the empty
Whereas the majority of these reactions will occur for all leaving groups with all nucleophiles, the reaction represented by the last nucleophile (the Claisen condensation) only occurs with esters.
chemistry.umeche.maine.edu /Solving/Snac.html   (154 words)

  
 Chapter 8 Notes
Nucleophilicity: a kinetic property measured by the rate at which a Nu attacks a reference compound under a standard set of experimental conditions
Because all nucleophiles are also bases, we study correlations between nucleophilicity and basicity
Relative nucleophilicities of halide ions in polar aprotic solvents are quite different from those in polar protic solvents
chem.pdx.edu /~wamserc/C334F99/8notes.htm   (548 words)

  
 Nucleophilic Substitution   (Site not responding. Last check: 2007-11-03)
Their reactions are characterised by nucleophilic substitution of the halogen atom, owing to polarity of the carbon
With primary and secondary halogenoalkanes, the reaction is very slow at ordinary temperatures, but rapid with tertiary halogenoalkanes.
The tertiary halogenoalkane first ionises in the slow step, followed by the rapid addition of the nucleophile to the intermediate carbocation.
www.avogadro.co.uk /organic/nucleo-sub.htm   (268 words)

  
 Nucleophilic Aromatic Substitution
Reaction is favoured by electron withdrawing substituents on the ring in order to decrease p–electron density and facilitate approach of a nucleophile.
This is due to fluorine being more inductively electron withdrawing than iodine, reducing electron density on the aromatic ring and enhancing the rate of nucleophilic attack.
This effect permits regioselective substitution with substrates possessing two identical leaving groups situated at different sites relative to the activating groups.
users.ox.ac.uk /~mwalter/web_05/year2/arom2/nuc_sub_arom.shtml   (224 words)

  
 NUCLEOPHILIC SUBSTITUTION
The purpose of this experiment is to investigate the relative rates at which a group of organic compounds undergo nucleophilic substitution reactions.
The nature of the carbon bearing the leaving group, the nature of the leaving group, the solvent system, and the nature of the nucleophile all play a role in determining the substitution pathway followed and the rate of the process.
The formation of a precipitate indicates a positive reaction between the alkyl halide and ethanolic AgNO3 due to the formation of ethanol-insoluble AgCl or AgBr.
www.muhlenberg.edu /depts/chemistry/chem201woh/ALKYLHAL.html   (691 words)

  
 Chemistry 610, Organic Reactions
(1) nucleophilicity is a kinetic property while basicity is normally considered in thermodynamic terms
(2) in nucleophilic reactions the Lewic acidic atom is a carbon instead of a proton
(b) hydrolysis with hydrazine takes advantage of [[alpha]]-nucleophile effect - nucleophiles with [[alpha]] heteroatoms are especially reactive in attacks on sp2 carbons.
www.chem.tamu.edu /rgroup/singleton/chem610/C3lecB32.html   (1089 words)

  
 CMS—VNS-TATB   (Site not responding. Last check: 2007-11-03)
In 1998, the Department of Energy funded a joint project with LLNL and BWXT Pantex to develop a new approach to making TATB, using the vicarious nucleophilic substitution (VNS) methodology developed by LLNL chemists.
Mitchell, P. Pagoria, R. Schmidt, U.S. Patent 5,633,406, “Vicarious Nucleophilic Substitution Using 4-Amino-1,2,4-triazole, Hydroxylamine or O-Alkylhydroxylamine to Prepare 1,3-Diamino-2,4,6-trinitrobenzene or 1,3,5-Triamino-2,4,6-trinitrobenzene,” May 27, 1997.
Mitchell, P. Pagoria, R. Schmidt, U.S. Patent 5,569,783, “Vicarious Nucleophilic Substitution to Prepare 1,3-Diamino-2,4,6-trinitrobenzene or 1,3,5-Triamino-2,4,6-trinitrobenzene,” October 29, 1996.
www-cms.llnl.gov /s-t/vns_tatb.html   (628 words)

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