Abstract
AFTER a long controversy, the space group of azulene is now apparently established as the centro-symmetrie P21/a, with two non-centro-symmetric molecules in the unit cell1,2, a result which leads to a disordered structure in which successive azulene molecules in the crystal are reversed in direction at random. Two previously observed cases of random positioning, namely, between chlorine and bromine in p-chlorobromobenzene3 and between methyl and chlorine in 2-amino-4-methyl-6-chloropyrimidine4, involve atoms or groups of comparable size, and are not as surprising as is the case of azulene, where there is a rather large difference in size between the five- and seven-membered rings.
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SHARMA, B., DONOHUE, J. Crystal Structure of 2-Phenylazulene. Nature 192, 863–864 (1961). https://doi.org/10.1038/192863a0
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DOI: https://doi.org/10.1038/192863a0
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