Different relative rates for photo-rearrangements of (E)- and (Z)-β-nitrostyrene derivatives to oximinoketones

New details on photochemistry of β-nitrostyrene derivatives are found, using a 500 MHz NMR spectrometer, instead of the formerly employed UV spectroscopy, where simply photo-rearrangement of (E)-β-methyl-β-nitrostyrene, 1E, to 1-phenyl-1,2-propanedione-1-oxime, 2, as well as cis–trans isomerization of (E)-β-nitrostyrene, 3E, to (Z)-β-nitrostyrene, 3Z, were reported. Here, using similar conditions such as light intensity, relative rates are found for cis–trans isomerization of 1E to (Z)-β-methyl-β-nitrostyrene, 1Z; as well as novel photo-rearrangements of: 1Z to 2; 3Z to 1-phenyl-1,2-ethandione-1-oxime, 4; and 3E to 4. 1H NMR preliminary kinetic analysis show isomerization of 1E to 1Z occurring at a relative rate of ki-Me = 0.083 s−1. Both 1E and 1Z go through a nitro-nitrite photo-rearrangement to 2 with relative kr-Me = 0.011 s−1 and k′r-Me = 0.070 s−1, respectively. Under the same conditions, photo-isomerization of 3E to 3Z takes place at relative ki-H = 0.011 s−1. The rates of photo-rearrangements of 3E as well as 3Z to 4 are measured with relative kr = 0.025 s−1 and k′r = 0.010 s−1, respectively.