chemia - Studia

TO WHAT EXTENT THE NMR “MOBILE PROTONS” ARE RELEVANT FOR RESTRICTED ROTATIONAL …
R a
R
N N
SER 4
N N N D
6
ε' H H
(s-s) b
N N γ
4
SER H
N 6 N N
Hγ'
D
(4-a-6-s) b
R = Cl
Axial anchorage
of D N-ligand in
I-2a
I-2b
I-2c
Content of blocked rotamers (%) c
a-a
62.0
56.5
52.0
4-s-6-a
19.5
19.5
23.0
4-a-6-s
16.5
16.0
18.0
s-s
2.0
8.0
7.0
R
β' N N
4
H
N 6 N N D
SER H β
(4-s-6-a) b
R
α' N N α
4
H
H
N 6 N N
SER D
(a-a) b
a R = Cl, in series I-2, II-3; piperazin-1-yl in series I-4, II-5
b Descriptors s (syn) and a (anti) are used with respect to
orientation of "open-chain" SERinolic and "closed-chain
"Dioxanic N-ligands vs. R.
c Throughout percentages deduced from the 1 H NMR
spectra performed at room temperature in [D 6 ]DMSO
using signals of the indicative protons D-NH (α, β, γ)
and SER-NH (α', β', γ', ε') (see Table 2, Table 3).
α' β’ γ’ε’
Equatorial anchorage
of D N-ligand in
II-3a
II-3b
II-3c
s-s
62
67
57
4-s-6-a
19
18
21
4-a-6-s
19
15
22
a-a
-
-
-
Cl
2
N N γ
4
(HOH 2 C) 2 (H 3 C)C
H 7.44 ppm
N 6 N N
O 2 N
5' H
γ' H H O O
H
6.46 ppm
4' H
H H
I-2a (4-a-6-s)
Scheme 2
Figure 1. 2D- 1 H, 1 H-NOESY chart of
compound I-2a (500 MHz, [D 6 ]DMSO)
The “trans” analogue I-2a (4-s-6-a)
was deduced logically, since its
incidence was comparable. The
major rotamer I-2a (a-a) was
preliminarily established by
considering the two closed SER-
NH δ values, signals α’ and β', in
their anti local environment: 6.74
ppm in I-2a (4-s-6-a, signal β') and
6.86 ppm in I-2a (a-a), signal α'
(Table 2). If so, in the syn local
environments, rotamers I-2a (4-a-
6-s), I-2a (s-s), the δ values of
protons SER-NH are also very
related, 6.46 (signal γ') and 6.41
(signal ε') respectively. It is to note
that compound I-2a was the single
case that made possible the
rotamerism recognition based on
NOESY Experiment.
39