Label the electrophilic and nucleophilic sites in each...

Key Concepts

Electrophilic Sites

These are regions in a molecule that are electron deficient, typically due to the presence of a positive charge or a partial positive charge resulting from electronegative atoms or polar bonds. Electrophilic sites seek electrons from other molecules or ions, which causes them to act as electron pair acceptors during chemical reactions. Understanding the nature of electrophilic sites is crucial for predicting where a molecule is likely to be attacked by electron-rich reagents.

Nucleophilic Sites

These are regions in a molecule that are rich in electrons, often due to the presence of lone pairs or negative charges. Nucleophilic sites donate electron pairs to electrophilic centers during chemical reactions, serving as electron pair donors. Identifying nucleophilic sites involves analyzing the electron density distribution within a molecule, and this concept is fundamental in mechanisms such as substitution and addition reactions.

Transcript

00:01 This is the answer to chapter 3, problem number 49, from the smith organic chemistry textbook.

00:09 And in this problem, we are given six molecules, and we're asked to identify the nucleophilic and electrophilic sites in each molecule.

00:20 And so we should remember that nucleophiles are going to be areas of electron density and electrophiles.

00:32 Are going to be areas of poor electron density.

00:38 So nucleophiles are going to be electron rich, electrophiles are going to be electron poor.

00:44 And so in this particular problem, we really are going to encounter two types of nucleophiles.

00:52 So anytime we see a lone pair, we can pretty safely say that that's going to be a nucleophile.

00:58 But then also when we see these double bonds in some of these molecules, we should remember that a double bond is an area of increased electron density and is therefore going to be able to act as a nucleophile.

01:12 And so in a, we have an iodine atom as part of this molecule, and the iodine atom has three lone pairs on it.

01:21 And so it's going to be the nucleophile here.

01:29 And since iodine is electronegative and it's pulling electron density, away from the carbon to which it's bound, that carbon is going to be electron poor, and as we said, that is going to be the characteristic of an electrophile.

01:46 So this carbon that is bound to the iodine is going to be the electrophile here.

01:51 So then in b, we don't have loan pairs anywhere, but we do have a double bond, and so that double bond is going to be able to act as a nucleophile.

02:03 And since we don't really have a corresponding area of low electron density to go with our nucleophile here, we're not going to have an electrophile in this case.

02:16 So looking at c, we have an oxygen with two lone pairs on it.

02:20 And as i said, at the beginning, we can pretty safely say that that's going to be a nucleophilic site there, the oxygen and its lone pairs.

02:28 And then again, similarly to the iodine carbon bond in part a of this problem, the carbons that are bound to the oxygen are going to be electron deficient because the oxygen is pulling their electrons away from them.

02:46 And so each of them is going to be a potentially electrophilic site.

02:52 Okay.

02:54 And then moving on to d, we have four double bonds in d.

03:00 And so those are going to be areas of electron density.

03:05 So all four double bonds are nucleophilic.

03:11 Oh, man...

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