Conceptual Genchem and Orgo

[nixon13]

---

Members do not see this ad.

I think it will be a good idea for people to start posting CONCEPTUAL question for the chemistrys. I am about to go to the bar right now so I cant but someone start it and I will follow up with more. This will be a sweet thread and very helpful. 😀

 

[alanan84]

I think this is a good idea. Obviously we're not advocating posting actual DAT questions but something useful to get the idea would be helpful. Conceptual makes the questions sound easy to me, but I'm sure they're not. Any examples?

 

[Contach]

wtf is a conceptual question? isn't any calculation also based on a concept? like calculate the osmolarity of NaCl. you have to know the concept that NaCl dissociates into Na+ and Cl- therefore the von't hoff factor is 2.

Regardless.. I'm going to pick this out of my ass and you tell me if this is a conceptual chemistry question.

What is most basic?
a) Aniline
b) Ammonia
c) Ammonium
d) N,N-dimethyl-ethanamine
And please explain why?

Thanks - I do not know the answer to this question.

 

[PreDent2009]

1.Which acid has the lowest pKa?
A.

B.

C.

D.

2. Which is the most acidic of these compounds?

A.

B.

C.

D.

3. Vitamin C has the following structure and a pKa value of 4.1.

Which -OH in vitamin C contains the acidic proton? 1, 2,3 or 4.

4. The rings in the structure below can be considered substituents on the other ring. The orientation of the rings can be described as:

A. cis
B. trans
C. one cis, one trans
D. neither
and
A. equatorial
B. axial
C. a combination of axial and equatorial
D. neither
​

 

[211183]

B
A??
1
B
A

 

[Contach]

B
A??
1
B
A

I'm going to have to confirm the answers except for 2 which I want to respectfully disagree on.
1 - B
2 - D (think keto-enol tautomerization)
3 - 1
4a - B
4b - A

 

[xhamburgersamx]

I'm going to have to confirm the answers except for 2 which I want to respectfully disagree on.
1 - B
2 - D (think keto-enol tautomerization)
3 - 1
4a - B
4b - A

yeah #2 is definitely D - there are alpha hydrogens.

 

[Tina324]

For #3, why isn't the answer Hydrogen 3? When that gets pulled off, you get conjugation.

Also #4 why is it not cis?

 

[hersheyslove]

I'm going to have to confirm the answers except for 2 which I want to respectfully disagree on.
1 - B
2 - D (think keto-enol tautomerization)
3 - 1
4a - B
4b - A

i think 3 is 2 since it have a resonance form if it lost the H atoms, no??

 

[PreDent2009]

Correct answers:

1. B
2. D
3. 2
4. Trans, equatorial

1.Which acid has the lowest pKa?
A.

B.

C.

D.

2. Which is the most acidic of these compounds?

A.

B.

C.

D.

3. Vitamin C has the following structure and a pKa value of 4.1.

Which -OH in vitamin C contains the acidic proton? 1, 2,3 or 4.

4. The rings in the structure below can be considered substituents on the other ring. The orientation of the rings can be described as:

A. cis
B. trans
C. one cis, one trans
D. neither
and
A. equatorial
B. axial
C. a combination of axial and equatorial
D. neither
​

 

[doc3232]

Thanks for the questions...this thread will get very long and annoyingly so can we start a new one soon?

1. Br pulls electrons from the molecule making it more acidic. Because electrons cannot be used to bond to a Hydrogen.

2. Resonance in which if one of the alpha carbons loses a Hydrogen then resonance will be made between the double bond and the carbonyl.

3. If the H on the (2.) Oxygen leaves then the electrons can move to the location of the double bond and then those electrons can go up between the carbon above and the carbonyl. Then the electrons between the C double bond O then move up to the Oxygen...

4th one is easy enough.

 

[Dencology]

great guys. keep this up. i will post some qs soon.

 

[Retimo]

Thanks for the questions...this thread will get very long and annoyingly so can we start a new one soon?

2. Resonance in which if one of the alpha carbons loses a Hydrogen then resonance will be made between the double bond and the carbonyl.

Word, not to prolong the subject, but I'm confused on the reasoning behind #2. I agree with the answer, but someone said "because it has alpha hydrogens." Don't they all have alpha hydrogens? And doc, with respect, how does the resonance play out? From what I see, after removing an alpha hydrogen, then you can bounce that negative charge between one carbon and it's closest oxygen. But all of the other molecules have the same resonance pattern. I don't see how the extra oxygen contributes to resonance. ..... Or maybe you can put the double bond between the two carbonyl carbons, leaving both O's negative and a postive alpha carbon? This doesn't seem likely. Am I missing something?

I originally thought the same answer but because of induction. The extra carbonyl is electron withdrawing, thus stabilizing it's electron-rich half. Any thoughts?? (ha, again, sorry to prolong!!)

 

[Contach]

Word, not to prolong the subject, but I'm confused on the reasoning behind #2. I agree with the answer, but someone said "because it has alpha hydrogens." Don't they all have alpha hydrogens? And doc, with respect, how does the resonance play out? From what I see, after removing an alpha hydrogen, then you can bounce that negative charge between one carbon and it's closest oxygen. But all of the other molecules have the same resonance pattern. I don't see how the extra oxygen contributes to resonance. ..... Or maybe you can put the double bond between the two carbonyl carbons, leaving both O's negative and a postive alpha carbon? This doesn't seem likely. Am I missing something?

I originally thought the same answer but because of induction. The extra carbonyl is electron withdrawing, thus stabilizing it's electron-rich half. Any thoughts?? (ha, again, sorry to prolong!!)

I agree, I don't think that explanation works. That's why in my post I said keto-enol tautomerization so you start with a alpha-keto hydroxy alkene... aka just make one of the keto's into an enol. then you have conjugation. if you take the proton off from the other side, you have the carbanion.. move that to a double bond and you have a conjugated diene... very stable. in addition from here you can delocalize a lot of the charges..