S1 SUPPORTING INFORMATION Intramolecular O-H···O Hydrogen Bond-Mediated Reversal in the Partitioning of Conformationally-Restricted Triplet 1,4-Biradicals and Amplification of Diastereo-differentiation in their Lifetimes Jarugu Narasimha Moorthy,* ,† Subhas Samanta, † Apurba L. Koner, § Satyajit Saha † , and Werner M. Nau* ,§ † Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, INDIA moorthy@iitk.ac.in § School of Engineering and Sciences, Campus Ring 1, Jacobs University Bremen, 28725 Bremen, GERMANY w.nau@jacobs-university.de Table of Contents 1. General aspects S3 2. Experimental procedures for the syntheses of ketones S3-S11 3. General procedure for the photolysis of ketones and characterization of photoproducts S12-S18 4. Procedure for deacetylation followed by esterification of 9-syn-CB1 and characterization of the products S19 5. Laser-Flash Photolyses and X-Ray crystal structure determinations S20 6. The crystal data for 9-anti, 8-anti-CB1, 9-anti-CB1, 9-anti-CB2, 9-syn-CB1-b and 9- syn-CB-2 S21 7. References S22 8. Absorption spectra of ketone 3-9 S23-S24 9. Transient absorption spectra of 1,4-biradical derived from Valerophenone S25 10. 1 H and 13 C NMR spectra of 3-methyl-1,4-diphenylbutan-1-one (5) S26-S27 11. 1 H and 13 C NMR spectra of 3-methoxy-1,4-diphenyl-1-butanone (6) S28-S29 12. 1 H and 13 C NMR spectra of 3-acetoxy-1,4-diphenyl-1-butanone (7) S30-S31 13. 1 H and 13 C NMR spectra of 3-methoxy-2-methyl-1,4-diphenyl-1-butanone (8-anti) S32-S33