✍ Scribed by Arthur J. Ashe III; Woon-Tung Chan; Timothy W. Smith
No coin nor oath required. For personal study only.
Spectroscopic measurements indicate that arsabenzene 1, the arsenic analog of pyridine, displays a high degree of aromatic character.
1 Thus 1 H-nmr spectrum shows that arsabenzene possesses a diamagnetic ring current. 2 Gas phase structural data indicate a planar ring with aromatic C-C bond distances of l.395i.3 UV photoelectron spectra4 supported by various MO studies, 495 are in accord with this aromaticity. However, the chemical demonstration of the aromaticity has been more modest,6*7 and in particular no electrophilic aromatic substitution reactions have previously been reported.
7 We now wish to report that arsabenzene will undergo facile Friedel Crafts acylation.
Acetylation of arsabenzene at -70" in CH2C12 with CH3COC1-A1C13 gave up to 80% isolated yield of monoacetylarsabenzenes.
Although we have been unable to separate this mixture using a variety of g.1.p.c. columns, the 'H-nmr spectrum showed two acyl methyl groups (6(C6D6) 2.13, 2.37) in the ratio of 4:l. However, the simple 'H-nmr spectrum of the major isomer established that it was 4-acetylarsabenzene 1: gl H-nmr (6(C6D6) 2.13 (3H,s);
8 .22 (2H,d,J=lOHz), 9.38(2H,d,J=lOHz).
Similarly the nmr spectrum of the mixture suggested that the minor component was the 2-isomer 2.
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