Pyrrole molecular structure

Fig. 1. Molecular structure of compound 1. The diazo group in 1 is coplanar to the pyrrole ring and the C(3)—N(2)—N(3) angle is 171(1)°.

Hydrodemetallation pathways for Ni-etioporphyrin and Ni-tetra(3-methylphenyl)porphyrin are shown in Fig. 20. Both are characterized by a sequential hydrogenation-hydrogenolysis global mechanism, but important differences are apparent. Ware and Wei (1985a) rationalized the differences in porphyrin reactivity on the basis of porphyrin molecular structure. Structural differences on the periphery of the metalloporphyrin, in particular the substituent groups at the /3-pyrrolic and methine bridge... 

To test the effect of a heteroatom, Starokon et al. [175] studied three five-membered heterocycles with a similar molecular structure, containing the oxygen (2,5-dihy-drofuran), nitrogen (3-pyrrole) and sulfur (butadiene sulfone). Only the oxygen-containing cycle was carboxidized selectively, while the others showed a strong tendency towards side reactions resulting in a set of unidentified products. 

Figure 1 Schematic representation of the molecular structure, numbering of atoms, and designations of pyrrole rings of cobalamins. R = Me is methyl B12 R = Ado is adenosyl-cobalamin (coenzyme B12) X = CN is cyanocobalamin (vitamin B12). Five-membered rings are labeled A-D, and the amide side-chains are labeled a-g.

Besides to introduce substitutents onto the ra ophenyl ring or the P-pyrrolic positions, modification of the molecular structures by fusing a small aromatic ring to the porphyrin ring has also been an attractive way to extend the absorption spectra and tune the electrochemical properties of porphyrins in the prospect of improving the sensitization behavior. Imahori has investigated the application of a fused five-membered porphyrin (84) as sensitizer in DSSC. Compared with the reference porphyrin, the fused porphyrin shows broaden and red-shifted absorption spectra... 

Mansuy (40) has characterized structurally a six-coordinate iron(II) N-alkylporphyrin. Figure 6 presents the molecular structure of this novel complex in which the strained six-coordinate geometry is stabilized by the formation of two five-membered chelate rings. The substituted pyrrole rings are canted a remarkable 50° from the mean equatorial plane as defined by the four pyrrole nitrogens. 

Figure 5 Molecular structure of selected organoalkoxysilanes trifunctional A-3-trimethoxy-sily 1-propyl-pyrrole (6) difunctional polydimethylsiloxane (7) a multifunctional bridged polysilsesquiox-ane (8)...

Crystal and molecular structure of pyrrole-2-carboxylic acid Ji-electron delocalization of its dimers-DFT and MP2 calculations102... 

Figure 3.56 Molecular structure of the syn diastereomer of the face-to-face porphyrin Co2FTF 4-2, 1N-H, where the 4-atom struts are linked to the [3-pyrrole positions of the rings. The ordering of the groups in the struts is different to that in L in Scheme 3.2.

Figure 7.12. Molecular structure of a hairpin pyrrole-imidazole tetramer.

A consideration of the results of molecular structural determinations of furan,194 pyrrole,196 thiophene,196 and selenophene197-198 shows that bond alternation as exemplified by the ratio (R) of the C-2-C-3 to C-3-C-4 bond lengths decreases in the order, furan (R = 0.950), selenophene (R = 0.956), pyrrole (R = 0.959), and thiophene (R=0.964). Whether this corresponds to an aromaticity scale,189 considering that the bond angles at the heteroatom are widely divergent, is a matter for debate. The X-ray structure determination199 of 1,2,5-triphenylphosphole is discussed later. 

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