NMR Help

[DDS4tehwin]

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



A. CH3CH3
B. CH3CI3
C. CH3I
D. CH2I2
E. CHI3


I dont seem to get these types of problems. Can someone please give a quick rundown on these types of questions?

 

[kevin512]

E is the answer, CHI3. Downfield means less electron density. Since I is very EN find the carbon with the most I's attached to it. Check out exam krackers for help.

 

[Dentalicous1234]

E is the answer, CHI3. Downfield means less electron density. Since I is very EN find the carbon with the most I's attached to it. Check out exam krackers for help.

but Ch3Cl3 is also there...and isn't Cl more electronegative than I and you said less e- density but I is bigger than Cl so doesn't it have more?

 

[PD3]

but Ch3Cl3 is also there...and isn't Cl more electronegative than I and you said less e- density but I is bigger than Cl so doesn't it have more?

The question says CH3CI3. This has no H's attached to the carbon, thus does not show up.

 

[moralbrain]

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



A. CH3CH3
B. CH3CI3
C. CH3I
D. CH2I2
E. CHI3


I dont seem to get these types of problems. Can someone please give a quick rundown on these types of questions?

I remember seeing this proble either from topscore or achiever..NMR question asking about downfield is all about deshielding effect from the e- withdrawing atoms(halogen) attached. Alswer is E because having 3 Iodine with one hydrogen gives you the max effect of deshielding..in contrast, electron donating atom, such as silicon would shiled the nucleus giving opposite effect (high field).