1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
The intermediates as well as the product were fully characterized and the corresponding
data shall be discussed in the following.
114
Br
N
NH HN
N
NO 2
a.
CN
N
NH HN
N
NO 2
b.
CO 2 H
N
NH HN
N
88 89
90
Scheme 54. Access to 15 4 -nitro-substituted porphyrin ethanoic acid 90. Applied conditions:
a. 1. Zn(OAc)2, CH2Cl2/MeOH, 15 h, rt; 2. KCN, PEG400, 24 h, rt; 3. aq. HCl, CH2Cl2, 10 min, rt;
b. HOAc/H2SO4/H2O, 96 h, 95 °C.
3.2.8.2.2 Characterization of 15 4 -Nitro-Substituted Precursor Systems 88, 89 and 90
The behavior of those compounds concerning mass spectrometry is well comparable to the
other porphyrin precursor systems as they do not tend to fragment. Thus, the molecular
peaks for [M] +· appear always clearly resolved at m/z = 935 (88), m/z = 881 (89) and
m/z = 900 (90), respectively. Only in the bromomethyl compound 88, a minor fragment can
be detected at m/z = 854 due to the loss of the bromine atom.
The NMR spectra show up typical for porphyrins with AB2C substitution pattern with four
resonances for the β-pyrrolic protons appearing as doublets with characteristic two-bond
couplings around 4.7 Hz. Also within this series of compounds, the alteration of the side
chain from bromomethyl over cyanomethyl to carboxymethyl causes significant changes of
the spectra. The corresponding regions of the 1 H NMR spectra are depicted in Figure 44.
The spectra appear strictly dependent on the size of the altered side chain as the signals of
the freely rotatable phenyl rings (10 & 20) are concerned. While for the smallest moiety
(-CH2CN in 89), the signals appear as two clear doublets at 7.77 and 8.13 ppm, the slightly
larger -CH2Br group in 88 gives rise to a splitting of the resonance signals, but only for the
protons in ortho positions in respect of the porphyrin core. For the largest side chain
(-CH2CO2H in 90), both resonance sets (for ortho and meta protons) are split into two
doublets each as then the two half-spaces above and below the porphyrin plane appear
clearly different and so do also the chemical shifts for the corresponding protons. That effect
NO 2