Evidence for a ladenburg benzene intermediate in the photo-isomerization of 1,2,4,5-tetra-t-butylbenzene to 1,2,3,5-tetra-t-butylbenzene

✍ Scribed by Edward M. Arnett; J.Martin Bollinger

• Publisher: Elsevier Science
• Year: 1964
• Tongue: French
• Weight: 263 KB
• Volume: 5
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)89358-8

✦ Synopsis

1,2,4,5-Tetra-l-butylbenzene (394) (TTBB) is believed to be a highly strained boat-shaped molecule (4) (I) and so might be expected to undergo photoisomerisation to a Dewar benzene (II) more readily than does 1,2,4-trit-butylbenzene(5'6), which was the first compound reported to undergo such a conversion. We find, in fact, that upon mild irradiation it is converted to a number of products, including 1,2,3,5-TTBB (V) and its related Dewar benzene (IV). To our knowledge, V is the first reported example of an aromatic system bearing three very bulky groups on adjacent carbon atoms. As might be expected, it gives evidence of being more highly strained than the starting compound (I); and its formation here, along with IV, will be shown as evidence in support of Burgstahler's recent suggestion (7) that intermediates with the Ladenburg (8) "prismane" nucleus may be involved in photo-rearrangements of some benzene systems.

Upon examining the irradiation products of I, we were surprised to find an isomeric tetra-t-butylbensene. Although previously reported poly-rbutylbenzenes with adjacent t-butyl groups have shown rather normal benzene spectra in the ultraviolet region (the main point of interest being a decrease in the intensity and fine structure of the band in the 270 tip region (3)) , the new compound or> has a spectrum more like that for a highly distorted