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Topic: SN1 reaction

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  SN1 reaction - Wikipedia, the free encyclopedia
1 reaction is an substitution reaction in organic chemistry.
It involves a carbocation intermediate, and it is commonly seen in reactions of secondary or tertiary alkyl halides, or (under strongly acidic conditions) with secondary or tertiary alcohols.
If the reaction is performed under warm or hot conditions (which favor an increase in entropy), E1 elimination is likely to predominate, leading to formation of an alkene.
en.wikipedia.org /wiki/SN1_reaction   (772 words)

 Nucleophilic substitution - Wikipedia, the free encyclopedia
In chemistry, nucleophilic substitution is a class of substitution reaction in which an electron-rich nucleophile attacks a molecule and replaces a group or atom, called the leaving group.
It is a fundamental class of reaction in organic chemistry, where the reaction occurs at a carbon centre, but nucleophilic substitutions are also well known in inorganic covalent compounds too.
R-Br + OH → R-OH + Br Nucleophilic substitution reactions are commonplace in organic chemistry, and they can be broadly categorised as taking place at an aliphatic (saturated) carbon or at (less often) an aromatic or other unsaturated carbon centre.
en.wikipedia.org /wiki/Nucleophilic_substitution_reaction   (725 words)

 Chapter 4 : SN1 mechanism
In an SN1 there is loss of the leaving group generates an intermediate carbocation which is then undergoes a rapid reaction with the nucleophile.
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.
In an SN1, the nucleophile attacks the planar carbocation.
www.chem.ucalgary.ca /courses/351/Carey/Ch04/ch4-3-1.html   (491 words)

 Substitution Reaction   (Site not responding. Last check: 2007-11-03)
The rate of reaction is dependent on the concentration of both the substrate and the nucleophile.
1 reaction depends only on the concentration of the organic halide, for the nucleophile is weak and cannot displace the halogen.
2 reactions, a good leaving group is electronegative to polarize the carbon atom, stable with an extra pair of electrons once it has left, and polarizable, to stabilize the transition state.
www.chemistry.emory.edu /mccormick/reports/substitution.htm   (982 words)

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.
The suggestion for reaction 2 is that the leaving group blocks access to the front side of the molecule, forcing the nucleophile to approach the substrate from the back side, leading to predominant inversion of configuration.
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)

 The Sn1 Reaction
A gentle or less effective nucleophile is the most effective because it will allow the reaction to occur more readily.
It is called unimolecular because the rate of the reaction depends on only one species.
In order to answer this question, it is important to remember that the more stable the carbocation, the quicker the reaction.
facultystaff.vwc.edu /~jeaster/courseinfo/Tutorials/reactions/Sn1.htm   (310 words)

 SN1 reaction : SN1
1 reaction is an organic reaction in chemistry.
Increasing or decreasing the concentration of that kind of molecule in a closed system[?] changes the rate of the reaction in a direct relationship[?].
Formation of a carbocation: due to the separates of leaving group (molecule A) from the carbon.
www.factspider.com /sn/sn1.html   (299 words)

 Summary of SN1 and SN2 reactions   (Site not responding. Last check: 2007-11-03)
1 reaction takes place in a sequence of steps, involving first the rate determining cleavage of the bond between carbon and the leaving group to form a carbocation, followed next with attack by a nucleophile.
The E1 reaction takes place in a sequence of steps, involving first the rate determining cleavage of the bond between carbon and a leaving group to generate a carbocation, followed next with abstraction of an adjacent hydrogen by a base to yield a double bond.
The E2 reaction takes place in a single, concerted step, in which a base abstracts a hydrogen while a double bond is being formed as the leaving group leaves with its electron pair.
www.odu.edu /sci/jadamski/n11ll.htm   (539 words)

Molecules undergo an SN1 reaction when the carbon attached to the leaving group is a tertiary carbon(meaning it is attached to three other carbons).
In all SN1 reactions this phenomenon occurs because when the nucleophile comes in to attack the carbocation intermediate(remember the carbocation is flat like a pancake) it is equally as likely that the nucleophile can come in and attack from the top as it is from the bottom.
If the hill is made into a smaller one (as it is when an SN1 reaction is run in a protic solvent) then the reaction is run much faster because it takes a shorter amount of time to cross a smaller hill.
www.organicchemistryreview.com /sn1.html   (1433 words)

 Curly arrows: nucleophilic reactions
In the Brønsted reaction, hydroxide ion displaces bromide ion from HBr.
2 reaction is favoured by basic nucleophiles such as hydroxide ion and disfavoured by protic solvents such as alcohols and water.
The rate of reaction is found to be independent with respect to the concentration of the nucleophile.
www.abdn.ac.uk /curly-arrows/org/n1.htm   (1178 words)

 Nucleophilic Substitution & Elimination
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.
2 reactions, i.e., tertiary and secondary alkyl halides.
1 reaction is not sensitive to the concentration or strenght of the nucleophile we can avoid the strong bases which promote elimination.
chemistry2.csudh.edu /rpendarvis/SN1Elim.html   (2034 words)

 SN1 and E1 Reactions
They each involve the formation of a carbocation as the crucial intermediate in the rate-determining step; these reactions exhibit unimolecular (or "first-order") kinetics, because only one molecule -- the immediate precursor of the carbocation -- is involved in the rate-determining step.
In fact, these reactions are typically performed under "solvolysis" conditions, i.e., simply heating the starting material in a protic solvent (an alcohol or carboxylic acid) that can also act as a nucleophile.
elimination reactions are either impossible, or reactions conditions have been adjusted in such a way that elimination reactions are suppressed.
www.personal.psu.edu /faculty/t/h/the1/sn1ande.htm   (1031 words)

 The SN1 reaction   (Site not responding. Last check: 2007-11-03)
1 reaction is a two-step reaction which is not stereospecific.
After Br has moved away from the central carbon of the tert-butyl group, the so-called carbocation becomes a flat structure (as can be seen on the right); consecutive attack by a nucleophile, like water, can occur from both sides of the structure.
In the next part, you will see that certain reactions can take place during the lifetime of the carbocation, between the bond dissociation and nucleophilic attack.
cheminf.cmbi.ru.nl /wetche/organic/sn1/sn1intro.html   (189 words)

 SN1   (Site not responding. Last check: 2007-11-03)
This process is called an elimination reaction and since this mechanism involves only one species in the rate determining step, it is called an E1 reaction.
We have seen an example of this reaction in the preparation of alkenes by dehydration of alcohols.
Attack of a nucleophile on the carbocation (SN1).
people.uis.edu /gtram1/organic/alkylHalides/sn1.htm   (351 words)

In the reaction of the trans isomer, the phenoxide attacks from the back, the same side as the methyl group on the adjacent carbon.
In the reaction of the cis isomer, when the phenoxide comes in from the back, it is attacking from the side opposite the methyl group on the adjacent carbon.
1 reaction is determined by how fast the carbocation forms, consider the relative stabilites of the carbocations formed from each of the starting materials, and assume the compound that would give the more stable carbocation will react faster.
www.muhlenberg.edu /depts/chemistry/chem201woh/HOPA1108A.htm   (1503 words)

 [No title]
The first theme focuses on the nature of reaction conditions in influencing the course of reaction and the second is purely a look at how mechanisms are verified.
The purpose of this experiment is to compare the relative nucleophilicities of the chloride ion and the bromide ion in two different reactions.
We know that the slow step in this reaction is the expulsion of the leaving group and that the rate of reaction depends only upon the concentration of the substrate.
www.naz.edu:9000 /~organic/fall/fallorganic/labstuff/fallexp10.htm   (1637 words)

 commonion   (Site not responding. Last check: 2007-11-03)
2 reactions (that is, for detecting the presence of an intermediate), is sensitivity of the rate to "common-ion rate suppression".
That is, "k" is the initial rate of the reaction divided by [RCl].
In this case the starting material is not depleted by the reaction with added chloride, because this reaction is just substitution of one chloride for another, so there is certainly no reason to slow an S
www.chem.yale.edu /~chem125/125/NucleophilicSn/CommonIon/commonion.htm   (888 words)

 VRML SN1 Reaction   (Site not responding. Last check: 2007-11-03)
The VRML scene below is a demonstration of the SN1 reaction between iodide ion and tert-butyl chloride.
To see the reaction, click the "Ionize" button and then try to add the nucleophile to the resulting carbocation.
the reaction is stepwise - there are two distinct steps: ionization, followed by nucleophilic addition of the nucleophile to the carbocation.
www.sienahts.edu /~swathen/vrml/sn1.html   (159 words)

 SN1 Reactions   (Site not responding. Last check: 2007-11-03)
Relative Rate studies have been conducted which shows that the Reaction Rate of an SN is increased with hogher substitution of the organic substrate such as an alkyl halide.
Studies have shown that the reaction rate increases in an SN reaction if the solvent is a polar protic solvent with a high dielectric constant.
Since the Rate Law for an SN reaction is first order in respect to the Organic substrate (alkyl halide), we should not expect a change in the concentration of the nucleophile to have any effect on the reaction rate of a reaction occuring via the SN path.
members.aol.com /logan20/sn1.html   (1299 words)

 [No title]   (Site not responding. Last check: 2007-11-03)
An alkyl halide, R-X, serves as the reactant or "substrate" in almost all nucleophilic substitution reactions.
To determine when the reaction has proceeded to a certain extent, enough base is added to the reaction mixture to neutralize a small fraction of the acid produced.
The rate of a reaction increases with increasing temperature because of the greater kinetic energy of the reacting molecules.
science.csustan.edu /almy/3012/Sn1Sn2.htm   (2347 words)

 Ch 8 : SN1 mechanism
1 reaction, the rate determining step is the loss of the leaving group to form the intermediate carbocation.
A typical example is the reaction of HBr with a tertiary alcohol.
Note that this is the reverse of the reaction of an alcohol with HBr.
www.chem.ucalgary.ca /courses/351/Carey5th/Ch08/ch8-2.html   (652 words)

 bubbachuck76's Xanga Site
Interpreting the results for the different alkyl halide reactions requires that their structures be analyzed.
Sec-butyl chloride’s faster reaction than n-butyl chloride is simply a matter of sec-butyl chloride’s secondary carbocation to be more stable than n-butyl chlroide’s primary carbocation.
2 reaction, no carbocation intermediate is formed (which is why the solvent is polar aprotic acetone to prevent ionization).
www.xanga.com /bubbachuck76   (2297 words)

 [No title]   (Site not responding. Last check: 2007-11-03)
They are called Chapter overview Chapter 11: Alkyl Halide Reactions We will consider each reaction in detail discussing a variety of factors that ultimately determine which mechanism and which reaction occur in a particular reaction setting.
SN1 and E1 reactions also occur in competition with each other under the same set of conditions in the same reaction flask.
SN1 and E1 reactions occur by different mechanisms and under different experimental conditions than do SN2 and E2 reactions.
chemistry.uca.edu /faculty/manion/2401/chap11.doc   (2077 words)

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