Which is more acidic?

[topdent1]

---

Members do not see this ad.

Why is para-nitrophenol more acidic than meta-nitrophenol? I though that the closer the electron withdrawing group is to the electron donating group, the more acidic the molecule is.

 

[doc toothache]

www.mhhe.com/physsci/chemistry/carey/student/olc/ch24phenols.html - 23k

 

[osimsDDS]

Why is para-nitrophenol more acidic than meta-nitrophenol? I though that the closer the electron withdrawing group is to the electron donating group, the more acidic the molecule is.

This is how I think of it check this out itll help you it works every time:

OH = moderate electron donating group correct...
NO2 = strong electron withdrawing group

If NO2 is acidic and you add the OH electron donating group to it, it will make it less acidic because OH donates electrons to the ring, think of it as OH is throwing negative electrons to NO2 which makes it less acidic...So you want the OH group to be as far away from NO2 as possible to make it more acidic...

 

[topdent1]

I have another question.

How many stereoisomers exist for 2,3-dibromobutane?

I used 2^n formula (n= number of chiral centers). I put down four but the answer is three stereoisomers: the meso form and a pair of enantiomers. Whats the deal???

 

[osimsDDS]

I have another question.

How many stereoisomers exist for 2,3-dibromobutane?

I used 2^n formula (n= number of chiral centers). I put down four but the answer is three stereoisomers: the meso form and a pair of enantiomers. Whats the deal???

This one is tricky but i learned it the hard way as you are as well right now...

Basically you have CH3-CHBrCHBrCH3

ok so obviously as you know the 2 carbons 2,3 in the middle will be steriogenic centers and therefore you can use 2^n. BUUUT If you have the same molecule adjacent you will only get 3. It is a rule of thumb so remember it.

 

[Hugh Mannity]

osimsDDS, when do you take your DAT? I'm expecting at least 25/25/25 from how much you've been busting your @$$.

 

[topdent1]

This one is tricky but i learned it the hard way as you are as well right now...

Basically you have CH3-CHBrCHBrCH3

ok so obviously as you know the 2 carbons 2,3 in the middle will be steriogenic centers and therefore you can use 2^n. BUUUT If you have the same molecule adjacent you will only get 3. It is a rule of thumb so remember it.

Thanks for the reply but i still don't understand. What do you mean by 'same molecule adjacent.' Do you mean that if the Br are next to each other (which in this case they are) than the rule is N-1, N being the number of sterioisomers?

 

[Dencology]

when you say adjacent molecule your referring to the Br, right? so in this both Br's are adjacent to each other and this is why we have 3 stereoisomers instead of 4, right?

 

[osimsDDS]

osimsDDS, when do you take your DAT? I'm expecting at least 25/25/25 from how much you've been busting your @$$.

dude im scared im taking it july 18th, im really really scared...my worse subject is QR im expecting a 16 at most haha

 

[osimsDDS]

when you say adjacent molecule your referring to the Br, right? so in this both Br's are adjacent to each other and this is why we have 3 stereoisomers instead of 4, right?

the best thing to do is draw the molecule out thats what i did...dont just draw CH3CHBrCHBrCH3, you need to draw it out completely with Hydrogens coming off and Bromines and everything...then you will see that the Br's are adjacent to each other via the carbons...hope that helps

 

[topdent1]

Since we're on the topic of sterochemistry, what is regiospecific? Sterospecificity is formation of 2 isomeric compounds, steroselectivity is formation of a major product, but I can't understand what regio is.

 

[osimsDDS]

Since we're on the topic of sterochemistry, what is regiospecific? Sterospecificity is formation of 2 isomeric compounds, steroselectivity is formation of a major product, but I can't understand what regio is.

regiospecific is when you have 2 choices and it picks 1 choice more favorable (stability) its known as regioselectivity...

Example is markonikov addition it could add anti with UV, peroxides, etc and regular without those...