Organic Chemistry Odyssey Questions

[yoh95]

Chapter 8 #14

Can someone explain why this reaction is SN1 instead of SN2?

The reagent is a strong base+nucleophile (OH-), and the halide is secondary. The product is inverted...so wouldn't this be the ideal SN2 condition?

Answer choice says B (SN1) because an inversion has occurred

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[yoh95]

Chapter 9 #14

How did the grignard attack the lactone twice to get 4 more carbons attached? Isn't it just 2 more carbons?

 

[spdental]

Chapter 9 #14

How did the grignard attack the lactone twice to get 4 more carbons attached? Isn't it just 2 more carbons?

I don't have the subscription but let me see if I can help out:

It sounds to me like you're memorizing the reactions rather than the rules. A Grignard is a extremely strong base, therefore it will keep attacking until it can't anymore. I'm unsure what you mean by 4 more attached, but in the case of a lactone it will attack the ester and the ring will open, since it would be pointless to attack the ketone again an acidic group should then protonate the negatively charged oxygen.

I can't help with the first because I do not have the problem.

Hope this helps.

 

[yoh95]

I don't have the subscription but let me see if I can help out:

It sounds to me like you're memorizing the reactions rather than the rules. A Grignard is a extremely strong base, therefore it will keep attacking until it can't anymore. I'm unsure what you mean by 4 more attached, but in the case of a lactone it will attack the ester and the ring will open, since it would be pointless to attack the ketone again an acidic group should then protonate the negatively charged oxygen.

I can't help with the first because I do not have the problem.

Hope this helps.

Oh yes that helps...

 

[yoh95]

Chapter 10 #9

A side note says "if on a benzene ring keep the phenol"

Does anyone know what this means?

 

[yoh95]

Chapter 10 #21

I picked the right answer by intuition but wanted to know if there's a better way to picking the correct answer of "trans"

Since the single bond can rotate, are we also getting the cis product? Or does it have to do with the better position of bromine getting kicked off since it is a concerted mechanism?

I am half/half on this question I could've easily picked cis..

Thank you

 

[yoh95]

Chapter 10 #28

If a methyl group is attached on the oxacyclopentane...(pic attached) would the halide attack the less substituted side to make a primary halide? Or the more substituted side?

(With just 1 mol HBr)

 

[spdental]

Chapter 10 #21

I picked the right answer by intuition but wanted to know if there's a better way to picking the correct answer of "trans"

Since the single bond can rotate, are we also getting the cis product? Or does it have to do with the better position of bromine getting kicked off since it is a concerted mechanism?

I am half/half on this question I could've easily picked cis..

Thank you

You can't know the answer to this unless you know which way the methyl groups are going. The oxygen and bromine are more sterically hindered so they will be opposite from eachother. Knowing which way the methyl groups are will allow you to answer cis or trans.

 

[spdental]

Chapter 10 #28

If a methyl group is attached on the oxacyclopentane...(pic attached) would the halide attack the less substituted side to make a primary halide? Or the more substituted side?

(With just 1 mol HBr)

More substituted, a positive charge will make the bond between the oxygen and the more substituted carbon "longer" in order for the nucleotide to attack. This is a basic epoxide rule you should know.

 

[yoh95]

You can't know the answer to this unless you know which way the methyl groups are going. The oxygen and bromine are more sterically hindered so they will be opposite from eachother. Knowing which way the methyl groups are will allow you to answer cis or trans.

Well the answer is trans and the solution just looks like that.. what do you mean which way the methyl group is? Isn't it free to rotate..

 

[yoh95]

More substituted, a positive charge will make the bond between the oxygen and the more substituted carbon "longer" in order for the nucleotide to attack. This is a basic epoxide rule you should know.

I've never heard this... could you explain more?

Also would you agree it is the more substituted side? @orgoman22

Thank you

 

[spdental]

Well the answer is trans and the solution just looks like that.. what do you mean which way the methyl group is? Isn't it free to rotate..

Yes but they are chiral so they can be S or R depending on which way the methyl is going.

 

[spdental]

I've never heard this... could you explain more?

Also would you agree it is the more substituted side? @orgoman22

Thank you

That's the rule for epoxides (if it is in basic solvent it will go to the less steric, and if it's acid it will protanate and then go to the more substituted position) - take a look at the oxymercuration mechanism, I figured it was the same for a ring, but I could be wrong.

 

[yoh95]

That's the rule for epoxides (if it is in basic solvent it will go to the less steric, and if it's acid it will protanate and then go to the more substituted position) - take a look at the oxymercuration mechanism, I figured it was the same for a ring, but I could be wrong.

Oh I see what you're saying.. hmm I guess that would apply here thanks!

 

[yoh95]

Yes but they are chiral so they can be S or R depending on which way the methyl is going.

So do you mean if the two chiral centers are R R it would be cis, R S it would be trans??

 

[yoh95]

If a bond is less polar than another, why does that make the bond weaker? Wouldn't it be held close more tightly if they're less polar?

 

[yoh95]

Can anybody explain why CH3OH (polar protic) solvents are used for NaBH4
and why ethers are used for LAH?

I often have trouble understanding why some reagents need certain solvents.. any tips?

 

[yoh95]

Chapter 12 #33

Why does the phenol direct the diazonium salt?

I think I learned that the diazonium salt is a meta director..

Thanks

 

[DAT Destroyer]

Chapter 12 #33

Why does the phenol direct the diazonium salt?

I think I learned that the diazonium salt is a meta director..

Thanks

I am not sure where you learned that a diazonium ion is a meta director......perhaps you mean the NH3+ group, but certainly not a diazonium salt. these compounds are the cornerstone to many a synthetic procedure. For example, it allows us to easily add on an F atom...or an iodine, or a CN . When added to a very reactive compound such as an aniline derivative or a phenol, we see an azo coupling. The diazonium salt acts as a WEAK ELECTROPHILE when reacted with a highly reactive aniline derivative or a phenol. Consult any organic text to see the mechanism. It will show you the exact electron flow . The highly reactive anilines and phenols DONATE electrons into the benzene ring, allowing them to be good attacking species in this process.

Hope this helps.

Dr. Romano

 

[Wererew]

Hofmann rearrangement reagents are only strong base + Br/Cl + H2O?

Ch 16 #39 describes that LAH and H2O reducing only the carbonyl of the amide to be a Hofmann rearrangement product

Thank you