Q's on chem

[prsndwg]

Advertisement - Members don't see this ad

Can you please explain these to me

I chose B because A, C,D are all strong bases and should react the same! No?

Don't we need heat to make the double bond? that's why I chose none!

Can someone please explain to me that when dealing with determining R and S on fischer projections, why does the Hydrogen needs to be on the vertical if we are dealing with 3 carbons only? I am really confused.😕

 

[UndergradGuy7]

For C. NaOH splits to Na2+. It should be Na+. So that is wrong. D is also wrong Ba should be 2+ not 1+. So the answer is E. both c and d are wrong. It is just a matter of getting the charges right. NaOH if OH- is -1 then Na has to be +1 to have a neutral molecule.

Haven't started organic chem. and don't remember it too well so I won't attempt the second question.

 

[beatsdre]

http://answers.yahoo.com/question/index?qid=20080115065850AA2COD3

K so what im assuming- the OH gets protonated, and since there is an alpha hydrogen on the ch2, its sometimes is removed within the solution because it is acidic. Its removed and h20 is lg.

 

[hausee]

second one A?

first is alpha hydrogen go through condensation then the -oh group is not stable and under acid condition lost H2o forming double bond.

 

[prsndwg]

second one A?

first is alpha hydrogen go through condensation then the -oh group is not stable and under acid condition lost H2o forming double bond.

so if its under basic conditions, then heat is needed to form the double bond?

 

[UCB05]

so if its under basic conditions, then heat is needed to form the double bond?

My understanding is that the heat is needed due to the state of the intermediate. The intermediate product is a beta-hydroxy carbonyl. Under acidic conditions, the -OH group can be protonated. The resulting -OH2+ group is a good leaving group, and will result in the proper elimination reaction without any outside assistance. Under basic conditions, there is no H+ to protonate the -OH group. The reaction proceeds in a way similar to an E2 reaction, and since -OH is a bad leaving group, it requires a bit of energy for the rxn to bump off the -OH.

 

[prsndwg]

My understanding is that the heat is needed due to the state of the intermediate. The intermediate product is a beta-hydroxy carbonyl. Under acidic conditions, the -OH group can be protonated. The resulting -OH2+ group is a good leaving group, and will result in the proper elimination reaction without any outside assistance. Under basic conditions, there is no H+ to protonate the -OH group. The reaction proceeds in a way similar to an E2 reaction, and since -OH is a bad leaving group, it requires a bit of energy for the rxn to bump off the -OH.

thanks, Can you also please clarify my last Q in regards to R and S?

 

[Impulse155]

For the first question, if you look at the charges on them they are incorrect for C&D making the answer E (assuming im right).
Overall charge for A is 0
Overall charge for B is 0
C has different charges on the left and right side
As does D



And I havent taken orgo yet so I cant help you with the other one ;\

 

[UCB05]

thanks, Can you also please clarify my last Q in regards to R and S?

I'm not sure exactly what you're asking. The convention for assigning R/S configuration is to have the lowest-priority group in the back and then seeing the direction of descending priority of the remaining three groups. The vertical position in a Fischer projection represents that out-of-the-page position a Hydrogen should be at.