P-rr bonding

You might recall from Section 1.9 that a carbon-carbon triple bond results from the interaction of two sp-hybridized carbon atoms. The two sp hybrid orbitals of carbon lie at an angle of 180° to each other along an axis perpendicular to the axes of the two unhybridized 2py and 2pz orbitals. When two sp-hybridized carbons approach each other, one sp-sp a bond and two p-p -rr bonds are... 

The heterobenzenes of the group 15 elements (1-5) comprise a series in which elements of an entire column of the periodic table have been incorporated into aromatic rings. The comparative study of this series has been extremely valuable for evaluating p-p rr-bonding between carbon and the heavier elements.1 However, the heterobenzene series has two important limitations. Only arsabenzene has a well developed aromatic chemistry. Moreover, stibabenzene and particularly bismabenzene are so labile that it has been difficult to obtain derivatives stable enough for study. 

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