Chemical Shift Nonequivalence in Prochiral Groups
Geminal groups – paired ligands
Y-E-Y: CH2, C(CH3)2, CF2, SiMe2, P(CH3)2, …
Prochiral groups:
CMe Me
X
H
SiMe Me
X
H
CF3
C C 3
O
H
X
F
PMeO OMe
X
O
CH H
X
PhMe
X
HH C
PMe Me
Ph
M
NMe Me
X
Ph
NMe Me
X
A
X = rest of the molecule
M = transition metal fragment
A = Lewis acid
Chemical Shift Nonequivalence of Geminal Ligands in
Prochiral Groups
X
ClMe C
H
Chiral Group
X
MeMe C
H
Prochiral Group
X
MeMe C
X
C2 Group
Me, Me Homotopic
Equivalent (isochronous)
X
MeMe C
H
No σ present
Me, Me Enantiotopic
Equivalent (isochronous) in achiral media
Nonequivalent (anisochronous) in chiral
media
Me, Me Diastereotopic
Nonequivalent (anisochronous)
If X is chiral, the paired ligands
in a prochiral group are always
diastereotoppic
X
MeMe C
H
σ
Ir
Cl PMe2
Ph
PhMe2
P CO
Cl
Cl
Ir
PhMe2
P C
PhMe2
P Cl
CO
Cl
l
mer-Cl, trans-P fac-Cl, cis-P