Achiever SNS I questions

[Mstoothlady2012]

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I have few questions....

Q1 Which radical is more stable tertiary or allylic?

Can some one please explain this one to me....

Q2 Which of the following compounds will have its proton(s) shifted furthest and downfield on a 200 MHz 1H NMR spectrum? CHI3 or CH3CI3?


Q3 Which of the following description(s) is/are NOT true pertaining to the acid-base characteristics of glycine, H2NCH2CO2H?

I.
Insoluble in water

II.
One equivalent of base is sufficient to fully deprotonate one equivalent of glycine present in strong acid

III.
Predominantly zwitterion at isoelectric pH

For this question the answer is I & II but I think the answer should be I only. The way they have shown the glycine, NH3 is already deprotonated. So I thought now you only need 1 more equivalent of base to deprotonate COOH group.

Thanks in advance 🙂

 

[Maygyver]

I have few questions....

Q1 Which radical is more stable tertiary or allylic?

Can some one please explain this one to me....

Q2 Which of the following compounds will have its proton(s) shifted furthest and downfield on a 200 MHz 1H NMR spectrum? CHI3 or CH3CI3?


Q3 Which of the following description(s) is/are NOT true pertaining to the acid-base characteristics of glycine, H2NCH2CO2H?

I.
Insoluble in water

II.
One equivalent of base is sufficient to fully deprotonate one equivalent of glycine present in strong acid

III.
Predominantly zwitterion at isoelectric pH

For this question the answer is I & II but I think the answer should be I only. The way they have shown the glycine, NH3 is already deprotonated. So I thought now you only need 1 more equivalent of base to deprotonate COOH group.

Thanks in advance 🙂

For the first one. Resonace is more important than the number of subsitutents.

For the second one. Cl is more electronegative so it will be more downfield. ( I believe, could be wrong)

For the third. II is incorrect because in strong acid it will be H3NCH2CO2H with a positive charge on the N. So you will need 2 equivs to fully deprotonate.

 

[dleodyddlek]

"For the first one. Resonace is more important than the number of subsitutents.
-Yeap you're right. samething applies to radical and carbocation.

For the second one. Cl is more electronegative so it will be more downfield. ( I believe, could be wrong)
-be careful. many people read it wrong. CH3-Cl3 is not possible. it's not chlorine. It should be CH3-C-I3 being compared to CHI3. But your answer is right. CH3CI3 is more downfield.


For the third. II is incorrect because in strong acid it will be H3NCH2CO2H with a positive charge on the N. So you will need 2 equivs to fully deprotonate.
- exactly. you have two protonated site, both at N terminal and C terminal. so you need 2 equiv base to fully deprotonate :] "

 

[Mstoothlady2012]

"For the first one. Resonace is more important than the number of subsitutents.
-Yeap you're right. samething applies to radical and carbocation.
ooh!! I don't know somewhere I read tertiary is more stable than allylic. I have seen the exact same molecules (CH3)3C. > CH2=CHCH2. somewhere, and the answer was this. Anyways ok so you are saying it should be CH2=CHCH2. > (CH3)3C.

For the second one. Cl is more electronegative so it will be more downfield. ( I believe, could be wrong)
-be careful. many people read it wrong. CH3-Cl3 is not possible. it's not chlorine. It should be CH3-C-I3 being compared to CHI3. But your answer is right. CH3CI3 is more downfield.

Yea sorry its CH3 - C-I3. See that's what I thought too that CH3 - CI3 will be more downfiled than CHI3. But the answer in achiever is other way around.😕 Is this b/c since CHI3 doesn't have any neighbouring hydrogens it will only have 1 peak....but where? downfield or upfield? I can't really seem to have a good reason why I chose that answer. Can you explain plz?


For the third. II is incorrect because in strong acid it will be H3NCH2CO2H with a positive charge on the N. So you will need 2 equivs to fully deprotonate.
- exactly. you have two protonated site, both at N terminal and C terminal. so you need 2 equiv base to fully deprotonate
ahaaa!! I missed that strong acid part 🙄
:] "

Thanks!

 

[Maygyver]

Alright, the more downfield hydrogen peak will be the one that is closest to the electronegative atom. So in this one, CHI3, the H is located by 3 electronegative atoms. In the second one, the hydrogen is separated from the iodines by an extra carbon. In general, the further away from the electronegative the hydrogen is, the less effect the electronegative atom will have on the shifting of the hydrogen on the HNMR. I hope this helps.

 

[Mstoothlady2012]

Alright, the more downfield hydrogen peak will be the one that is closest to the electronegative atom. So in this one, CHI3, the H is located by 3 electronegative atoms. In the second one, the hydrogen is separated from the iodines by an extra carbon. In general, the further away from the electronegative the hydrogen is, the less effect the electronegative atom will have on the shifting of the hydrogen on the HNMR. I hope this helps.

Hmm I guess that makes sense. Thanks!