How Do Reactivities Compare in Key Organic Chemistry Compound Pairs?

[sparsh]

Discuss the difference in the reactivity between the following pairs of compounds :

1. Benzene and phenol with bromine
2. 1-hexanol and 2-hexanol with chromium trioxide in acid
3. ethylamine and acetamide in dil HCl
4. Sodium methoxide and sodium tert-butoxide with 1- bromopropane

Thanks

 

[gem0688]

Discuss the difference in the reactivity between the following pairs of compounds :

1. Benzene and phenol with bromine

Thanks

Think about what affect the -OH group will have on the benzene ring. Think about the lone pair of electrons on the oxygen and the delocalised electrons in the middle. What is going to happen?

Also give us some ideas of your thoughts or the work you have done on the questions and we can then tell you if you are right or not and help you more.

gema

 

[sparsh]

Well I had worked on these problems : ---

Sorry i knew the1st one. The OH group activates the benzene ring towards EAS and hence bromine will occupy all ortho,m,p positions (in aqeuous medium)

With Chromium trioxide (2nd one) oxidation takes place . So in the 1st aldehyde forms and in the second a ketone. But what will be the difference in the reactivity ?

I have no idea about the 3rd

I think the 3rd one is dehydrohalogenation rxn. Sodium methoxide is a strong base (CH3O-) so there will be Saytzeff rule followed and alkene will form . (Rearrangement can't take place as it is propane and alkene formed even after rearrangement is the same ) . Tertbutoxide is stearically hindered base but should it reduce reactivity ? I wanted something specific in this regard.

 

[siddharth]

Comparing the rates of reactions by theoretical reasoning for some of the reactions below is tricky.

I think , difference in reactivity, only means the differences in the final product.

Well I had worked on these problems : ---

Sorry i knew the1st one. The OH group activates the benzene ring towards EAS and hence bromine will occupy all ortho,m,p positions (in aqeuous medium)

Yep, that's right. But, I really think that such questions should mention the catalyst (like FeBr3).

With Chromium trioxide (2nd one) oxidation takes place . So in the 1st aldehyde forms and in the second a ketone. But what will be the difference in the reactivity ?

Yeah, that's right. I think the fact the products are different in each case, is the difference in reactivity.

I have no idea about the 3rd

Ethylamine will react to give the salt. While, acetamide will get hydrolysed to give an acid.

I think the 3rd one is dehydrohalogenation rxn. Sodium methoxide is a strong base (CH3O-) so there will be Saytzeff rule followed and alkene will form . (Rearrangement can't take place as it is propane and alkene formed even after rearrangement is the same ) . Tertbutoxide is stearically hindered base but should it reduce reactivity ? I wanted something specific in this regard.

Isn't this the Williamson synthesis of ethers?

 

[sparsh]

For the third one --

Ya can be that as well . But then what do we consider . The elimination product or the ethers ?

 

[siddharth]

It depends on other factors, like the reaction condition, solvent used, etc. So I don't know.

 

[GCT]

3. ethylamine and acetamide in dil HCl
4. Sodium methoxide and sodium tert-butoxide with 1- bromopropane

4) you probably need to distinguish between an elimination and nucleophilic substitution reaction for this one.