Determine the mechanism of nucleophilic substitution of each reaction and draw the products, inc

Determine the mechanism of nucleophilic substitution of each...

Key Concepts

Stereochemistry

Stereochemistry is the study of the three-dimensional arrangement of atoms in molecules and is crucial in understanding the outcomes of nucleophilic substitution reactions. In SN2 reactions, the inversion of configuration is a key stereochemical feature, whereas in SN1 reactions, the formation of a planar intermediate may lead to a mix of stereoisomers. The stereochemical effects directly influence the physical and biological properties of the reaction products.

SN2 Mechanism

The SN2 (bimolecular nucleophilic substitution) mechanism proceeds via a single concerted step where the nucleophile attacks the substrate simultaneously as the leaving group departs. This backside attack leads to an inversion of configuration at the chiral center and the reaction rate depends on the concentrations of both the nucleophile and the substrate.

Nucleophilic Substitution

Nucleophilic substitution is a type of chemical reaction where a nucleophile, a species rich in electrons, replaces a leaving group attached to an electrophilic carbon. This reaction forms the basis for many organic transformations and can proceed via different mechanistic pathways, each with distinct kinetic and stereochemical outcomes.

SN1 Mechanism

The SN1 (unimolecular nucleophilic substitution) mechanism involves a two-step process in which the rate-determining step is the loss of the leaving group, resulting in the formation of a carbocation intermediate. The nucleophile then attacks the planar carbocation, potentially from either side, which often leads to a racemic mixture when the carbon is chiral.

Transcript

0:00 Hi everyone.

00:01 So in order to tackle this question, okay, we'll see a first that is, so this would be first substitute is there or substrate is there.

00:31 H plus cn minus.

00:38 So this undergoescent to mechanism in presence of acetone as a solvent.

00:50 You'll get a product.

00:56 That is cs3 , then here is cyanide.

01:29 What is mechanism? mechanism of this reaction.

01:40 So in order to see the mechanism, we will first draw the substrate.

01:55 So in this case, you know, reaction is a sent to.

01:59 So nucleophile attacks from the side opposite to bromine.

02:05 So what you get is in other words a backside attack of a nucleophile takes place, backside attack of nucleophile takes place.

02:34 So it undergo ascent to reaction, backside attack, attack of cn minus to which bromine departs, but bromine is not attached to the chiral centre.

03:33 Bromene it is not attached to the chiral centre attached to the chiral centre.

03:52 So, so you can draw like this, stereochemistry is not taken into account, is not taken into account.

04:23 Then b, so you can draw like this, that is thick line indicates bromine is coming towards the observer or coming above the plate plus o minus ch3 this also undergo a second mechanism so in this case since the bromine is attached to the chiral carbon there is a inversion of configuration takes place so now we'll rate the mechanism.

05:38 No, what is mechanism basically? mechanism is step -by -step description of any chemical reaction.

05:53 So, you know, in this case, this is bromine.

06:00 Then this is hydrogen.

06:07 So, methoxodion, it attacks from the back side to which bromine departs.

06:32 So what we get is, so 100 % inversion of configuration takes place.

07:25 It takes place due to backset attack.

07:34 In first case also there is a b .r minus.

07:52 So, the s &2 mechanism, because bromine is at kyrr center, kyril carbon, 100 % inversion of configuration takes place takes place due to backside attack of o minus cs3 then we will move to the c part of the question that is here is here then ch2, ch2, ch2, cs3 plus cs3oh this procedure via sn1 mechanism.

09:36 So i'll get 2 product.

10:04 One is with a retention in configuration and one with inversion in configuration.

10:16 So this is 50 % you can say since it involved both retention and inversion, we can label it as a racemization.

10:38 A racemization takes place.

10:41 Now this mechanism, mechanism.

10:52 So you know we are then ch2, ch2, cs3.

11:16 So cbr becomes a bond becomes a polar in sn1 mechanism and therefore bromine first gets departed and she'll get a carbonium ion like this.

11:41 Now, you know, there are two possibility...