Physico-chemical Behaviour of Porphyrins in Aqueous Detergent Solutions 39 



o 



to that of the dimethyl ester of protopoq^hyrin itself, {A) in Fig. 1, as water molecules 

 rapidly displace the organic ligand from the complex. 



We have isolated the ferric sitting-atop complex in pure crystalline form. The 

 structure suggested in Fig. 2 was confirmed by the infra-red spectrum of this complex 

 dissolved in deuterated chloroform, 99% CDCI3. In protoporphyrin dimethyl ester 

 the N-H groups are responsible for three distinct infra-red absorption peaks at 3-05 fx 

 (stretching), 6-15 /< (deformation), and 9-06 // (rocking) respectively. In the infra-red 

 spectrum of haemin dimethyl ester all of the above three peaks disappear as expected. 



20 



15 

 10 

 05 

 

 20 

 15 

 10 

 OS 



■t ° 



c 



-o 20 

 8 15 



C,H 



COoCH, 



COXH, 



Fig. 2. Proposed sitting-atop type of 

 structure for the reaction intermediate. 



650 600 550 500 



Wavelength, m/i 



Fig. 1 



450 



We found that in the infra-red spectrum of the ferric sitting-atop complex the 3-05 

 and 6-15 [i peaks shifted to 3-11 and 6-64 /t respectively, and that the 9-06// peak is 

 no longer easily detectable. This observation confirms our proposed sitting-atop 

 structure, since it shows that the corresponding N — H bonds still exist in the said 

 complex. The observed frequency shift of the 3-05 and 6-15 /< peaks is presumably 

 due to the polarizing influence of the ferric ion. 

 Phillips: Wang's suggestion that the sitting-atop complex is involved in metal porphyrin 

 formation is both novel and interesting. However, I find the suggestion that the 

 dication structure involves two nitrogens each with two hydrogens and two nitrogens 

 without hydrogens rather disturbing for a number of reasons, viz. 



(i) the spectra of the dication and dianion are identical, which would seem to 

 support the symmetrical dication structure (i.e. 1 hydrogen per nitrogen atom); 



