Shielding Effect and Chemical Shift

  • Thread starter edimeo25
  • Start date
  • #1
6
0

Homework Statement


Given a molecule of chloroethene (vinyl chloride) or ClCH=CH2. Rank the hydrogen atoms in the molecule in terms of which will have the greatest chemical shift.


Homework Equations


None


The Attempt at a Solution


Since the Cl and the double bond are both electron-rich, this affects the shielding of each proton. So to rank them, I think it could go one of two ways:
1) The proton on the Cl-CH= is the most blinded (smallest chemical shift) since it is between the two electron-rich groups, followed by the proton in the cis position to the Cl since it is slightly closer to the electronic density than the H in the trans position to the Cl.
OR
2) The reverse order so: the H on the Cl-CH= is the least blinded (largest chemical shift) because the Cl is electronegative and is withdrawing the electron density from the H. Then the H in the cis position to the Cl would be 2nd rank in terms of blinding and then followed by the H in the trans position to the Cl (being the least blinded) because all of its electron density is being pulled toward the double bond and the Cl.

I think I'm a bit mixed up on how electronegativity works, so any help would be greatly appreciated. Thanks in advance!!
 

Answers and Replies

  • #2
chemisttree
Science Advisor
Homework Helper
Gold Member
3,432
460

The Attempt at a Solution


Since the Cl and the double bond are both electron-rich, this affects the shielding of each proton. So to rank them, I think it could go one of two ways:
1) The proton on the Cl-CH= is the most blinded (smallest chemical shift) since it is between the two electron-rich groups, followed by the proton in the cis position to the Cl since it is slightly closer to the electronic density than the H in the trans position to the Cl.
OR
No. Halogens are electron rich relative to a similar carbon group but they get that way in part because they withdraw electron density from the carbon they are attached to. Therefore, the remaining carbon is electron-deficient so the geminal C-H bond is polarized with more electron density being pulled toward the carbon. This effect is called de-shielding.
 

Related Threads on Shielding Effect and Chemical Shift

  • Last Post
Replies
0
Views
809
  • Last Post
Replies
1
Views
6K
Replies
5
Views
3K
  • Last Post
Replies
6
Views
4K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
1
Views
1K
Replies
3
Views
3K
  • Last Post
Replies
2
Views
3K
Replies
3
Views
7K
Top