Organic Chemistry Semester 1 LABORATORY MANUAL - Moravian ...

Nuclear Magnetic Resonance Appendix E19 Part V. Techniques and Theory
d. Examples:
(1.) Consider Figure 3: compound (8.) on E8
• Why are there 4 peaks for only 2 protons?
J AX
J AX
Cl Cl Cl
Cl C C C Cl
Cl H H
A X
A
X
• Explanation:
B o
Proton A experiences an effective magnetic field, B eff , which is made up of B o
(the external field), B el (the field produced by proton A's local environment) and B n (the
field produced by proton X).
H X
H X
antiparallel
(shielding)
B n
B n
parallel
(deshielding)
However, B n has 2 probable orientations
with respect to B o .
∴ ~ 1
2 of the H A's experience the B n
of H X parallel to B o (deshielding) and
~ 1
2 of H A's experience the B n of H X
anti-parallel to B o (shielding). So half of
the H A ’s absorb at a slightly lower
frequency and the other half at a slightly
higher frequency.
(2.) Consider Figure 3: Compound (9.) on E8
• Why are there 3 peaks for proton A?
X
X
Cl
Cl
C
Cl
C
H
C
Cl H H
A X
Cl
A