Chemical Shift Factors Affecting Chemical Shift in proton NMR spectroscopy. Factors Includes: Hydrogen bonding, Anisotropy effect, Elcertonegativity & inductive effect and Vanderwaal's Deshielding

1. PRESENTED BY :
KESHAV KUMAR SINGH
Reg. No.:- Y19266023
Deptt. of Chemistry
DHSGU Sagar (M.P.)

2.  The shifts in the positions of NMR signals resulting from
the Shielding / Deshielding by the Electrons is called as
“CHEMICAL SHIFTS”.
 As the shift is due to difference in the chemical
environment, it is known as chemical shift.

3. When a proton is present inside the magnetic field
more close to an electro positive atom more applied
magnetic field is required to cause excitation. This
effect is called shielding effect.
When a proton is present outside the magnetic field
close to a electronegative atom less applied magnetic
field is required to cause excitation. This effect is called
deshielding effect.

4.  Shielding shift
 At higher Magnetic field
strength(300MHZ,500MHZ)
 Deshielding shift
 At lower Magnetic field
strength(100MHZ,60MHZ)
Up
field
Down
field

5. Factor Affecting Chemical Shift

6.  The proton is said to be deshielded if its attached
with an electronegative atom/group. Greater the
electro negativity of atom greater is the deshielding
caused to proton. If the deshielding is more, then ‘δ’
value also more.
 Electronegative atoms like Halogens Oxygen and
Nitrogen deshielding the protons .
 There for the absorption occurs downfield.
 The deshielding is directly proportional to the
halogens oxygen or nitrogen.

7.  + I effect
 - I effect
 An electron withdrawing group is able to reduce
electron density around the proton and Deshields
the proton.
 An electron releasing group increase the electron
density around the proton and give rise to its
shielding.

17.  If an atom exhibits hydrogen boding in a compound .
 It will deshielded due to the strongly electronegative
atom attached to it
 So absorption in shifted downfield.
 Intra molecular hydrogen bonding .
 Inter molecular hydrogen bonding

20.  The electron cloud of a bulkier group will tend to repel the
electron cloud surrounding the proton.
 Thus such a proton will be deshielded .
 will resonate at slightly higher value of δ than expected in
the absence of this effect.