1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
3.2.3.2 NMR Investigations at Room Temperature
The 1 H NMR spectrum of free base system 53 shows up quite complex in comparison to the
precursor systems as those have appeared pseudo-symmetrical leading to a reduced
number of detected resonances. In this case, the C1 symmetry gives rise to a large number of
partly overlaid resonance signals as it is shown in Figure 17.
46
2
18
7
8
17
O
12+13
9.0 8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4
CDCl 3
N
NH HN
102/6
15 2/6
N
53
10 2/6 ,15 2/6
m-ArH
20 2/6
3 2 in
5 3
3 2 out
5 5
1.60 1.55 1.50
9 8 7 6 5 4 3 2 1 0 -1 δ [ppm] -3
Figure 17. 1 H NMR spectrum of 53, 400 MHz, CDCl3, rt. All signals are numbered according to
IUPAC recommendations.
The seven β-pyrrolic protons give rise to a set of one singlet and six doublets ( 3 J = 4.9 Hz)
most downfield between 9.0 and 8.5 ppm as it is to be expected for a C1 symmetric system
with one β-substituent. These signals can be nearly all assigned via COSY (Correlated
Spectroscopy) and NOE (Nuclear Overhauser Effect) experiments 46 as they appear well
resolved. In contrast, the ones for the arylic protons in between 8.5 and 7.3 ppm show a
significant line-broadening and thus are overlaid making a definite assignment impossible.
Only the protons on the tethered phenyl ring (5 3 and 5 5 ) are an exception as they give rise to
two doublets at 7.68 and 7.35 ppm ( 4 J = 1.7 Hz). This behavior corroborates the assumption
that the porphyrin system is bent as then the rotational barriers for the meso-aryl
5 2
15 4
10 4
20 4
NH
5 4