10.1021/jp026641t.s001 Carlos N. Sanrame Carlos N. Sanrame Christopher P. Suhrada Christopher P. Suhrada Hung Dang Hung Dang Miguel A. Garcia-Garibay Miguel A. Garcia-Garibay Photochemistry of Crystalline Chlorodiazirines:  The Influence of Conformational Disorder and Intermolecular Cl···NN Interactions on the Solid-State Reactivity of Singlet Chlorocarbenes<sup>†</sup> American Chemical Society 2003 compounds 4 b azine carbene 5 alkene 4 c term solution 13 C CPMAS NMR chlorodiazirine formation precursor biphenyl Cl diazirine analysis 2003-03-27 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Photochemistry_of_Crystalline_Chlorodiazirines_The_Influence_of_Conformational_Disorder_and_Intermolecular_Cl_N_N_Interactions_on_the_Solid-State_Reactivity_of_Singlet_Chlorocarbenes_sup_sup_/3724554 A photochemical study was carried out with 3-substituted 3-chlorodiazirines with 4-biphenyl- (<b>4a</b>), (4-biphenyl)methyl- (<b>4b</b>), 2-(4-biphenyl)ethyl- (<b>4c</b>), and 1,1-dimethyl-1-(4-biphenyl)methyl (<b>4d</b>) substituents. The chlorodiazirines were prepared from the corresponding amidines (<b>7</b>) by a procedure involving oxidation with <i>tert</i>-butyl hypochlorite under phase-transfer catalysis. The crystalline nature of <b>4a</b>−<b>d</b> was established by differential scanning calorimetric analysis, which revealed melting endotherms prior to thermal decomposition. Photochemical results in crystalline solids were analogous to those observed in solution, and the products were analyzed in terms of the corresponding singlet-state chlorocarbene intermediates (<b>5a</b>−<b>d</b>). Irradiation of <b>4a</b> in solution and in crystals resulted in formation of azine <b>9a</b> by reaction of carbene <b>5a</b> with its precursor. Equally selective, diazirine <b>4d</b> gave alkene <b>6d</b> as the only product by a 1,2-Ph migration from carbene <b>5d</b>. In contrast, irradiation of compounds <b>4b</b> and <b>4c</b> resulted in formation of two alkenes by 1,2-H shifts and formation of azines by reactions of the carbenes with their precursors. The low selectivity of <b>4b</b> was rationalized in terms of structural data from single-crystal X-ray diffraction analysis, which revealed two disordered diazirine conformers and close Cl···N contacts between adjacent molecules. Rapid conformational equilibration in the solid state was also suggested by solid-state <sup>13</sup>C CPMAS NMR. Similar structural effects are also postulated to account for the solid-state reactivity of <b>4c</b>.