Chemistry Reference
In-Depth Information
The equivalent bases in each HT form had H8 chemical shifts intermediate
between those of the nonequivalent bases in the HH form. Moreover the H8 signal
of the major HT form appeared downfi eld from the H8 signal of the minor HT
form.
76 - 78,82,104
The H8 chemical shift is infl uenced by the positioning of the H8 atom
with respect to the shielding cone of the
cis
G. The canting of the base in the direc-
tion that moves H8 away from the
cis
G will lead to less H8 shielding and hence to
a downfi eld H8 signal relative to the average H8 signal (this relationship is called
'6-in' because the six-membered ring of G moves closer to the
cis
G). In contrast,
a rotation of the base in the direction moving H8 toward the
cis
G will lead to
greater H8 shielding,
110
and hence to a more upfi eld H8 signal (this relationship is
called '6-out' because the six-membered ring of G moves further from the
cis
G,
Figure 5.7 ).
The G base of the HH form with O6 on the same side of the coordination plane
as the N-H of the
cis
amine had an upfi eld H8 signal (HH
u
), indicative of an H8
S
,
R
,
R
,
S
chirality of Me
2
dab or bip
P
P
P
P
O
O
N
Pt
N
N
Pt
N
N
Pt
H
O
O
O
O
P
P
Λ
HT (major)
∆
HT (minor)
HH
R
,
S
,
S
,
R
chirality of Me
2
dab or bip
P
P
P
O
O
P
N
Pt
N
N
Pt
N
N
Pt
N
O
O
O
O
P
P
Λ
HT (minor)
∆
HT (major)
HH
Figure 5.7
HT and HH conformers in Me
2
dab or bip-Pt(5
-GMP)
2
complexes having (
S
,
R
,
R
,
S
)
or (
R
,
S
,
S
,
R
) chirality at the carrier ligand. N-CH
2
X groups (X = H and R for Me
2
dab and bip,
respectively) are indicated by larger circles, N-H protons by smaller circles. Only the chelate
ring atoms of the carrier ligands are shown. 5
′
-GMP is represented by an arrow, the tip indi-
cating H8 and the tethered P the sugar-phosphate group
′
