Abstract
We studied the photochemical reactivity of salts of 4-(2,4,6-triisopropylbenzoyl)benzoic acid with propane-1,2-diamine (1), methanamine (2), cyclohexanamine (3), and morpholine (4), for compounds (1), (3), and (4) at 0.1 MPa and for compounds (1) and (2) at 1.3 GPa and 1.0 GPa, respectively. The changes in the values of the unit cell parameters after UV irradiation and the values of the intramolecular geometrical parameters indicated the possibility of the occurrence of the Norrish–Yang reaction in the case of all the compounds. The analysis of the intramolecular geometry and free spaces revealed which o-isopropyl group takes part in the reaction. For (1), the same o-isopropyl group should be reactive at ambient and high pressures. In the case of (2), high pressure caused the phase transition from the space group I2/a with one molecule in the asymmetric unit cell to the space group P1¯ with two asymmetric molecules. The analysis of voids indicated that the Norrish–Yang reaction is less probable for one of the two molecules. For the other molecule, the intramolecular geometrical parameters showed that except for the Norrish–Yang reaction, the concurrent reaction leading to the formation of a five-membered ring can also proceed. In (3), both o-isopropyl groups are able to react; however, the bigger volume of a void near 2-isopropyl may be the factor determining the reactivity. For (4), only one o-isopropyl should be reactive.
Highlights
The Norrish–Yang reaction is the photochemical reaction proceeding in compounds with a carbonyl group and a γ-hydrogen atom and leading to the formation of a four-membered ring (Scheme 1)
As the result of UV irradiation, the unit cell parameters of (1) change, which shows that the Norrish–Yang reaction occurs in the crystal (Figure 2 and Table 2)
While determining the crystal structure after 50 min of UV irradiation at 0.1 MPa, the maxima of difference electron density were observed evidencing the occurrence of the Norrish–Yang reaction with the participation of o-isopropyl at C2, i.e., 2-isopropyl
Summary
The Norrish–Yang reaction is the photochemical reaction proceeding in compounds with a carbonyl group and a γ-hydrogen atom and leading to the formation of a four-membered ring (Scheme 1). The reaction is induced by UV radiation, which causes the transfer of the γ-hydrogen to the carbonyl oxygen atom and the formation of a 1,4-diradical. Five parameters were introduced to describe this geometry, owing to which it is possible to predict the reaction occurrence [1,2]. These parameters are as follows: the distance between the γ-hydrogen atom and the carbonyl oxygen atom (d), with the ideal value less than 2.7 Å; Crystals 2018, 8, 299; doi:10.3390/cryst8070299 www.mdpi.com/journal/crystals
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