Add curved arrows to the following polar reactions to indicate the flow of electrons in each: a.

Add curved arrows to the following polar reactions to...

Key Concepts

Polarity in Reactions

Polarity in reactions refers to the distribution of electrical charge within molecules that creates areas of partial positive and negative charges. This uneven electron distribution makes some regions nucleophilic (electron-rich) and others electrophilic (electron-poor), which is critical in determining the direction of electron flow in polar reactions. Recognizing the polar nature of reactants helps in predicting how and where electrons will be transferred during a reaction.

Reaction Mechanisms

Reaction mechanisms describe the step-by-step sequence of events by which reactants transform into products. Each step involves the making and breaking of bonds, often mediated by the flow of electrons as depicted by curved arrow notation. Understanding the mechanism of a reaction allows chemists to predict intermediates, transition states, and the overall reactivity of the molecules involved.

Curved Arrow Notation

Curved arrow notation is a graphical method used in organic chemistry to represent the movement of electron pairs during chemical reactions. The arrows start where the electrons are initially located (often a lone pair or a bond) and point toward the destination where the electrons will form a new bond or be accepted by an electron-deficient atom. This notation is a fundamental tool in illustrating reaction mechanisms and understanding how bonds are broken and formed.

Transcript

00:01 Okay, so in this problem, you have several reactions where you have the reactants and the product, and you have to use arrows to show the movement of electrons.

00:15 And so for these problems, i think the easiest way to start is to identify your nucleophile and your electrophile.

00:24 And so remember that your nucleophile can either have a negative charge or be neutral, but it should have a lone pair of electrons.

00:36 So your nucleophile has to have an electron pair.

00:46 Your electrophile is going to either be positive or neutral, and it's going to be able to accept your electron pair.

00:59 And so let's look at this first example.

01:03 So this one is maybe a little bit tricky, because you have a lone pair of electrons on your nitrogen atom, and you also have lone pair of electrons on your chlorine atoms.

01:16 So the way that you want to think about this is your electrophile is also going to likely, or your electrophile needs some way to be able to accept electrons.

01:35 So it needs to be a type of electron sink.

01:38 And so usually what you'll see is your electrophile might also have a leaving group, which i'll abbreviate lg.

01:46 So if you look at ammonia, this nitrogen is bonded to three hydrogen atoms, and hydrogen is not a good leaving group.

01:54 However, this chlorine, cl2, does have a leaving group, and you can see in the product here that chlorine is a leaving group.

02:04 So if you look at your initial products, you have a leaving group, which would make this chlorine, your electrophile, and this nitrogen, your nucleophile.

02:19 So when you're drawing out your electrons, your arrow to show your electron movements, you want to always go from an area of high electron density to an area of low electron density, and basically from your nucleophile to your electrophile.

02:34 So your nucleophile, in this case, is your nitrogen, is going to attack your chlorine, and then your two electrons from this chlorine -clorine bond are going to be pushed to this chlorine.

02:48 So now that you have a new bond between this nitrogen and chlorine, which comes from this lone pair here, and you have this extra lone pair of electrons on this chlorine atom, which comes from this bond here.

03:05 Okay, let's look at a second example.

03:12 So in this case, we use a different color.

03:15 We have our oxygen with a lone pair of electrons and a negative charge.

03:20 This indicates to us that this is going to be our nucleophile.

03:26 So our oxygen is our nucleophile.

03:29 On this bromomethyl group, you have bromine because of the lone pair of electrons, is going to have a partially negative charge, rendering this carbon partially positive...

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