Distinguish between sn1 and sn2 mechanism of substitution reaction

Nucleophilic substitution reactions are those in which an electron-rich nucleophile approaches a positively charged electrophile in order to replace a leaving group. SN2 reaction mechanism SN2 stands for nucleophilic substitution bimolecular reaction. The term “biomolecular” implies that there are two reacting species in the rate-determining step of the reaction. When the rate of nucleophilic substitution reactions depends upon the concentration of substrate (e.g., alkyl halide) and nucleophile, then the reaction is of second order. Example: Kinetics of the SN 2 reaction The kinetic data show that the rate of the reaction is determined by the concentration of both reactants. i.e. Rate directly proportional to: [alkyl halide] [nucleophile] Rate = k [CH 3Br] [OH] – Since this reaction is of second order, it occurs by a direct displacement mechanism in which both reactants are present at the rate-determining step. Mechanism of the SN 2 reaction The nucleophile is supposed to target the side of the carbon atom opposite to that of bromine. This is known as a “backside attack.” As a result of this approach, a transition state with carbon atoms partially bonded to both the OH and Br groups is formed. The center carbon is sp2 hybridized in the transition state, and the three hydrogens connected to it are in the same plane with a bond angle of 120 °C. The reaction may be illustrated as follows: It should be observed that the hydroxide ion’s negative charge has decreased in the tran...

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Usually you are not expected to know the exact strength of a base, just its relative strength to other bases. The key to doing this is figuring out the stability of the conjugate acid of a base. The more stable a conjugate acid, the stronger the original base because it will have a higher tendency to gain a proton/give an electron pair. (The same is also true for strong acids and their weak conjugate bases.)Look online for a list of what makes conjugate acids and bases stable. Do Sn2 and E2 reaction favor an unstable carbon? I still don't get why? Can anyone explain for me why a primary carbon tends to have Sn2/E2 reactions? Is it because in Sn2/E2 mechanism, nucleophile attacks at the same time the leaving group leaves, so primary carbon (which has less stereohinderance) will result in faster reaction? A simple answer is that, in these mechanisms, ease of reaction matters. It is easier to, say, remove a bromine from a primary carbon than it is to remove it from a tertiary carbon when carbocations can't be formed. A complex answer is that: This is because 'pentavalent' transition states are formed (basically, the attacking center also latches onto the carbon from the opposite side in the transition state causing carbon to appear to have 5 bonds) This transition state requires a less hindered carbon, like a primary carbon over, say, a tertiary carbon. What I want to do in this video is to try to figure out what type of reaction or reactions might occur if we have-- what is ...

To understand the sn1 and sn2 reactions, it is necessary to understand the basic mechanism of nucleophilic substitution reactions. Nucleophilic substitution reactions are the reactions in which halogens are replaced by some other atoms or a group. It is also defined as the reaction in which a nucleus lover (nucleophile, having negative charge) may react with an electrophile (electron lover, having positive charge) and is replaced by a leaving group is called the Nucleophilic substitution reaction. Nucleophilic substitution reactions on alkyl halides involve two main reactions sn1 & sn2 reactions. In the last part of this blog, I will explain a brief difference between Sn1 and Sn2 reactions as a conclusion. Electrophile/Nucleophile An electrophile is basically a species that reacts with the nucleophile. It is an electron lover and has a positive charge on it. It is electron-deficient species that has a positive charge on it. All the electrophile acts as a lewis acid. Electrophiles mainly interact with the nucleophiles by addition or substitution reaction. But on the other hand, Nucleophile is the species having a negative charge on them. It is an electron-rich species and acts as a Lewis base. Leaving Group In a heterolytic cleavage, molecular fragments that depart with the pair of an electron is called leaving group. This leaving group may be an anion, cation, or neutral molecule. Also leaving group is the nucleophile which accepts a pair of electrons. More stable is the n...

S N ​ 1 S N ​ 1 Rate Law Unimolecular (substrate only) Bimolecular (substrate and nucleophile) Big Barrier Carbocation stability Steric Hindrance Alkyl halide (electrophile) 3 o > 2 o > > 1 o 1 o > 2 o > > 3 o Nucleophile Weak (generally neutral) Strong (generally bearing a negative charge) Solvent Polar protic (e.g alcohols) Polar aprotic (e.g DMSO, acetone) Stereochemistry Mixture of retention and inversion of configuration Inversion of configuration

In a substitution reaction an existing group on the substrate is removed and a new group takes its place. In an elimination reaction the group is simply removed and no new group comes to take its place and this usually results in a double or triple bond forming in the substrate instead. Hope that helps. I understand if you had a protic solvent, it would stabilize the strong base (to form weak acid) or the strong nucleophile. The protons would react with them. So in order to have an Sn2 or an E2, so you need an aprotic solvent. Aprotic solvent will favor Sn2 or an E2 reaction. But why does Sn2 favor strong nucleophile, and Sn1 favor weak nucleophile from the first place? In addition, does E2 favor strong base, and E2 favor weak base as well? I also don't get the reason. - [Instructor] When you're trying to determine between a substitution and an elimination reaction, it's important to consider the function of the reagent. Does your reagent function as a nucleophile or does it function as a base? So first let's look at nucleophile. Let's consider the idea of charge. We know that water can function as a nucleophile so we have a region of high electron density around the oxygen. The oxygen is partially negative because oxygen is more electrode negative than hydrogen so these hydrogens are partially positive. So water can function as a nucleophile, however it is a weak nucleophile because we do not have as high a region of electron density as we would with the hydroxide ion. So...

\( \newcommand\) • • • • • For a certain substrate, it may have chance to go through any of the four reaction pathways. So it seems rather challenging to predict the outcome of a certain reaction. We will talk about the strategies that can be applied in solving such problem, and explain the reasonings behind. It is very important to understand that the structural nature of a substrate (primary, secondary or tertiary) is the most critical factor to determine which reaction pathway it goes through. For example, primary substrates never go with S N1 or E1 because the primary carbocations are too unstable. If the substrate could go with a couple of different reaction pathways, then the reaction conditions, including the basicity/nucleophilicity of the reagent, temperature, solvent etc., play the important role to determine which pathway is the major one. Our discussions therefore will start from the different type for substrates, then explore the condition effects on that substrate. Primary (1 °) Primary (1°) substrates cannot go with any unimolecular reaction, that is no S N1/E1, because primary carbocations are too unstable to be formed. Since primary substrates are very good candidates for SN2 reaction, so S N2 is the predominant pathway when good nucleophile is used. The only exception is that when big bulky base/nucleophile is used, E2 becomes the major reaction. Examples of reactions for primary substrates: Figure 8.4a Reactions for primary substrates Secondary (2 °) It ...

SN1 vs. SN2 In Chemistry, there are plenty of technical issues to learn. One of which is the difference between SN1 and SN2 reactions. Actually, both SN1 and SN2 are Nucleophilic Substitution reactions, which are the reactions between an electron pair donor and an electron pair acceptor. In both types of reaction, a hybridized electrophile should have a leaving group (X), in During the SN1 type of reaction (two-step), a carbocation will initially be formed. It will then react with the nucleophile because it is free to attack from both sides; whereas, during the SN2 type of reaction, two molecules are involved in the actual transition state. The leaving of the departure group occurs simultaneously (one step) with the attack on the backside of the nucleophile. Due to this fact, it leads to a predictable configuration, and it can also be reversed. In both reactions, the nucleophile participates with the departure group. It is always better to study the properties of the departure group, and it is also worthwhile to study the factors that will determine whether the particular reaction follows a SN1 or SN2 pathway. The solvent that is used in the reaction also plays an The reaction of the SN1 pathway is highly feasible for compounds with tertiary substitution, since the corresponding tertiary carbenium ion is stabilized through hyper-conjugation. This is also because a carbenium ion is planar, less hindered, and more naturally reactive as opposed to the uncharged parent compoun...

Yes, there is always a mixture of R and S products when an SN1 reaction occurs. It happens because the carbocation is planar and can be attacked from either side to form an R,S mixture. They are not always formed in equal amounts, however. For example, in come complicated cyclic compounds, attack from one side might be more sterically hindered than from the other. Many molecules can function as both an acid and a base. The proton on the OH group can be removed by a strong base, so in this case the methanol is behaving like an acid (proton donor). The O of the OH group has lone pair electrons that can accept a proton and form an oxonium ion. In this case the methanol is behaving like a base (proton acceptor). So if the methanol is in the presence of a base, it can behave as an acid. If it is in the presence of an acid, it can behave as a base. 9:51 why one oxygen is more nucleophilic than the other oxygen. I have two dis-satisfaction with it. Shouldn't the fact that the other oxygen being closer to the carbonyn be a thermal-dynamic property and thus not strictly a kinetic property? Secondly, the first oxygen discussed is also right next to the same carbonyl which should similarly be partially positive. Then wouldn't the cause he described be common to both oxygens? I am suspecting another factor in play that Jay didn't mention is the resonance stabilization. There doesn't seem to be a very good resonance for the case when the second oxygen discussed is the attacking nucleop...