Deduce Major Product for Electrophilic Addition of Propene

Let's take a look at our discussion question this week!

221107 question

We want to determine the major product formed when propene reacts with iodine monobromide in concentrated aqueous sodium nitrate.

Notice this reagents and conditions is not in syllabus and we do not need to memorise it.

Therefore we have to apply our understanding of electrophilic addition of alkene to deduce the products formed.

Check out this video lesson to learn electrophilic addition of alkenes in detail.:

1. Deduce electrophile in Step 1

221107 deduce electrophile

Only iodine in IBr is partially positive charged and reactive enough to act as electrophile.

Na+ is very stable and hydrogen in water is relatively stable so we will ignore Na and H.

Therefore the first step of electrophilic addition will be:

221107 EA step 1

Electrophile iodine will join to carbon C1 with more hydrogen to form a more stable carbocation.

We can deduce this via modified Markovnikov Rule where electrophile joins to the carbon with more hydrogen during electrophilic addition of alkene to give the major product.

2. Deduce nucleophile in Step 2

Now the negative species Br- (from IBr), NO3- (from conc NaNO3) and OH- (from water) can attack the carbocation to form different products.

221107 deduce nucleophile and step 2

Since NO3- is concentrated, the probability of it attacking the carbocation is the highest to give the major product.

Therefore the major product formed will be option C.

221107 answer

Topic: Alkenes, Organic Chemistry, A Level Chemistry, Singapore

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