The chemical shifts observed in NMR spectroscopy result from differences in the chemical environment of nuclei that cause shielding or deshielding of protons from the magnetic field. Chemical shifts are measured in parts per million (ppm) relative to a reference standard. Key factors that influence chemical shifts include inductive effects, van der Waals deshielding, anisotropic effects, and hydrogen bonding. Protons adjacent to alkenes or alkynes experience anisotropic deshielding or shielding respectively, while hydrogen bonding causes downfield shifts depending on bond strength.

1. FACTORS INFLUENCING
CHEMICAL SHIFT
Presented by: B.Kavita
Under the guidance of
Dr.K.Shanta Kumari, M.Pharm,Ph.D

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

4. 10
TMS
 Measured in DELTA & TAU scales.
 The value of chemical shift is expressed in terms of “ppm”(parts per million).
DELTA
TAU 0
Chemical shift, ppm δ = Shift in (Hz)
Spectrometer frequency (in MHz)

5. FACTORS AFFECTING CHEMICAL SHIFT
INDUCTIVE EFFECT
VANDERWAALS
DESHIELDING
ANISOTROPIC EFFECT
HYDROGEN BONDING

6. INDUCTIVE EFFECT
 Greater the electronegativity.
 Greater is the deshielding.
 Delta value will be more.

7. VANDERWAALS DESHIELDING
 The Electron cloud of the bulky group will tend to
repel,the electron cloud (in over crowded molecules)
surrounding the proton , & the proton is deshielded .

8. ANISOTROPIC EFFECT
The opposite of isotropy which means uniformity
in all directions.
So, anisotropy is non-uniformity.
Now for different compounds this anisotropy is
different as different distribution of electrons
around nuclei.
Anisotropy effect of
 Alkene
 Alkyne
 Benzene
 ketone/Aldehyde

9. ALKENES:
 protons adjacent to alkene (C=C-H)are
deshielded by anisotropy effect,so, chemical
shift will be induced.

10. ALKYNES:
 All groups in a molecule having πelectrons generate
secondary anisotropic field.
 In alkynes the system will shields the proton,thus
causing decrease in chemical shift of alkynes.
 Also the proton next to the alkynes carbon experience
the anisotropic effect towards shielded side.

11. HYDROGEN BONDING
 Downfield shift depends upon the strength of
H-bonding
 Intra-molecular H-bonding doesn’t show any
shifting absorption

12. APPROXIMETE CHEMICAL SHIFT RANGE (ppm)
FOR SELECTED TYPES OF PROTONS

13. REFERENCE
 Organic spectroscopy by WILLIAM KEMP.
 Spectroscopy by SILVERSTEIN.
 Instrumental methods of chemical analysis by
GURUDEEP R.CHARWAL.
 Introduction to spectroscopy by DONALD L .
PAVIA.