Organic chemistry test

[ecoli]

this is the practice final, and I don't understand all the answers... please help me understand. Thanks

 

3. Which of the following will be the principal organic product that results when a solution of 0.1 mol of ethyl chloroformate, EtOCOCl, is slowly added to a solution of 0.1 mole of phenylmagnesium bromide, followed by hydrolysis with dilute aqueous acid?

• 
   
  A. Ph3COH
  B. PhCO2Et
  C. PhCOCl
  D. PhCOPh
  E. PhOEt

 

Answer choice A. But why does the phenyl group react three times? Does it have anything to do with the aqueous acid attacking the carbonyl oxygen?

 

4. Which one of the ketones below would be expected to have the greatest amount of aromatic character?

 

 

To me, it looks like they all have aromatic character, except for E, but the answer is given as D.

 

5. What is the approximate equilibrium constant for the reaction

 

CH3CH2MgBr + PhC(=O)NH2 → CH3CH3 + PhC(=O)NH- MgBr+ ?

 

• 
  A. 1051
  B. 10-35
  C. 10-16
  D. 1016
  E. 1035

I don't really understand how equilibriums work with amino acids, which have multiple pKas. The answer is given as E.

 

8. Which of the following would be the principal product of addition of HCl to pulegone?

 

 

Answer is B. But why wouldn't the acid react with the carbonyl oxygen? I though that would be more reactive than the double bond, and would be protonated over it.

 

9. Which of the following hydride reducing agents selectively reduces acids and esters, but not aldehydes and ketones?

 

A. DIBAL-H, [(CH3)2CHCH2]2AlH

B. LiAlH4

C. NaBH4

D. NaBH3CN

E. NaH

 

The answer is A... but I don't remember why or learning this in class. What makes A so special that it doesn't reduce aldehydes or ketones?

 

The amino acid proline is synthesized in the body from glutamate, as shown in the scheme below. Questions 14-16 relate to this scheme.

 

 

15. Which steps in the proline biosynthesis are likely to involve NADH or NADPH?

 

A. B, C, and D

B. A and B

C. B and C

D. B and D

E. C and D

 

 

 

The answer is choice D. I understand how that works for step D. But, what about B... I don't see how the reduction works in that step. How does the hydrogen get added on?

 

 

 

And that's it for the multiple choice section. I would appreciate any and all help provided.

[brockrhodes]

4. Which one of the ketones below would be expected to have the greatest amount of aromatic character?   To me, it looks like they all have aromatic character, except for E, but the answer is given as D.

 

When they want to know the greatest amount of aromatic character they're asking for the most continuous hyper-conjugation. D makes sense because it is a benezene ring with a carbonyl. It appears that the additional carbonyl on C deactivates the ring. Neither B or E are aromatic. A is, but it's not as hyperconjugated as D.

 

That's all I have time for right now.

[ecoli]

[bubble=Ecoli]

 

When they want to know the greatest amount of aromatic character they're asking for the most continuous hyper-conjugation. D makes sense because it is a benezene ring with a carbonyl. It appears that the additional carbonyl on C deactivates the ring. Neither B or E are aromatic. A is, but it's not as hyperconjugated as D.

 

That's all I have time for right now.

How is D benzene?.. it's got 7 carbons. And aren't B and E aromatic due to Keto-enol tautomerization?

[brockrhodes]

Good show, I'm a boob. Either that or I was smoking something when I first responded.

 

Hahaha. You're right. It's not benzene. It does have 7 carbons. However, it still has the greatest amount of hyper conjugation. I think you're right about B as well, but not E. I don't see how the tautomerization would lead to an active ring with E.

[ecoli]

Good show, I'm a boob. Either that or I was smoking something when I first responded.

 

Hahaha. You're right. It's not benzene. It does have 7 carbons. However, it still has the greatest amount of hyper conjugation. I think you're right about B as well, but not E. I don't see how the tautomerization would lead to an active ring with E.

 

oh right, just b, not E... However, I was under the impression that a seven carbon species was automatically disqualified from the (4n+2) rule... is that not true?

[brockrhodes]

Yeah, 4n + 2 can not = 8. It certainly has 8 electrons in the pi system. I didn't even bother with Huckel because I was just drawing resonance structures in my head. I wrote them down on paper and I can't seem to avoid a 5 bonded carbon connected to the oxygen, including double bonds to each adjacent carbons. I also didn't look too hard because you said the answer given is D, so I figured it was aromatic and they just wanted the most extensive hyperconjugation, but now I don't even think it is aromatic. What do you call that? 2, 4, 6, cycloheptatrienone? It seems like that ring would be unstable, but maybe the 7th carbon keeps it together.

[gc]

For question 4 (about aromaticity) try drawing some resonance structures...then you should hopefully be able to figure it out