PROBING CHEMICAL-TRANSFORMATIONS IN ORGANIC-SOLIDS VIA NMR TECHNIQUES - THE SOLID-STATE PHOTODIMERIZATION REACTION OF 7-METHOXY-4-METHYLCOUMARIN

It has been reported that crystalline 7-methoxy-4-methylcoumarin undergoes a [2 + 2] photodimerization reaction to give two different products; the major product is the syn head-head dimer, whereas the minor product is the syn head-tail dimer. In this paper, high-resolution solid-state C-13 NMR and solution-state H-1 and C-13 NMR techniques have been applied to investigate various structural issues relating to this solid-state photodimerization reaction. In particular, spectra have been recorded at various stages during the progress of the photodimerization reaction with the aim of charting the structural changes in the system as a function of reaction progress, with particular interest in assessing the potential of this technique for investigating the structural reasons for the production of the minor product. Conformational and dynamic properties of the product obtained in this solid-state photodimerization reaction have also been assessed.