Carbon-hydrogen bonds pyrrole

With phenolic ethers (16) and certain pyrroles (17), carbon disulfide (1) will insert into the nucleophilic carbon-hydrogen bond by a Friedel-Crafts-type reaction (Scheme 9). 

The hydrogen-bonding abilities of the ring nitrogen atom have also been the subject of investigation using IR spectroscopy, with proton donors such as phenol, pyrrole, and acetylenes in dilute carbon tetrachloride solution. Good correlations are observed 128-131 thus Eq. 

The general effect of NH-X hydrogen bonding on the NMR spectrum of pyrrole is to shift the a-proton resonance to lower field and to lea re the /3-proton resonance relatively unchanged from its position when the spectrum is measured in carbon tetrachloride. This effect should be compared with the characteristic upfield shift of the a-proton resonance and downfield shift of the /3-proton resonance which results from the formation of NH-7T complexes (see Section III, B, 3, a). 

In many of the haemoproteins we shall be discussing, the protoporphyrin IX group is held to the polypeptide chain only by hydrogen bonding, Van der Wools forces and iron-protein bonds. In several other cases, notably in cytochrome-c and its related compounds, the haem is covalently linked to the protein via substituents at the pyrrole carbon atoms. Cyto-chrome-c can be regarded as an iron protoporphyrin IX group with the addition of a protein cysteine side-chain across the vinyl double bonds giving two thio-ether links (Fig. 3). 

Carbon dioxide exhibits properties typical of hydrocarbon solvents, such as toluene however, for basic molecules, such as pyrrole, CO2 provides more hydrogen bonding basicity than do hydrocarbon solvents. No significant difference in polarity can be detected between the liquid and supercritical phases. It is hoped that this view of CO2 as a hydrocarbon solvent with unusual properties (infinite compressibility in the supercritical state, low surface tension and viscosity, low... 

---