Photochemistry within Organic Capsules
Photochemistry is the speciality of chemistry that investigates the interactions between matter and light. In this speciality, the two important photo-induced reactions of carbonyl compounds are Norrish Type I (photochemical cleavage) and Type II (photochemical intramolecular abstraction of a γ-hydrogen)1.
Photochemistry is the study of chemical processes which involves the absorption of light by an atom or molecule. The guest molecule(s) take place in the water-soluble cavitand with four carboxylic acid groups at both the top and the bottom as a photochemical reaction container, which is known as Octa acid (OA). In this container, the availability of free space plays a critical role within the confined capsule. For the purpose of controlling free space available for the reactants, the investigation of photochemical reactivity of several para-alkyl dibenzyl ketones captive within a water-soluble organic capsule (octa acid) has been conducted2.
- NMR experiment: The Octa acid and guest ketones 1c-1f were synthesized, and complete complexes were formed.
- Photochemical experiment: A solution of 0.001M hexane in a Pyrex tube was bubbled with nitrogen gas for 30 min before it was sealed with a rubber septum and irradiated by a mercury (Hg) lamp for 30 minutes
Results and Discussion
- H-NMR analysis: The ketone and octa acid complexes indicated an upward shift in the guest signals. The diffusion coefficient of free octa acid was higher than that of different complexes, also had a 2:1 ratio between the guest 1c-f and hosts in both the 1D and 2D NMR.
- Photochemical results: Radiating the ketone resulted in the formation of a primary radical pair. All the guest molecules formed in-cage products, and the ratios between the carbonylated and decarbonylated products varied greatly.
For the purpose of controlling free space available for the reactants, the investigation of photochemical reactivity of several para-alkyl dibenzyl ketones captive within a water-soluble organic capsule (octa acid) has been conducted. This aids to the knowledge of cage effect and the importance of capsular free space within a photochemical organic capsule.
(1) Ramamurthy, V. Photochemistry within a Water-Soluble Organic Capsule. Abstr. Pap. Am. Chem. Soc. 2016, 251.
(2) Sundaresan, A. K.; Ramamurthy, V. Consequences of Controlling Free Space within a Reaction Cavity with a Remote Alkyl Group: Photochemistry of Para-Alkyl Dibenzyl Ketones within an Organic Capsule in Water. Photochem. Photobiol. Sci. 2008, 7 (12), 1555–1564. https://doi.org/10.1039/b814001d.