title: Photoinduced C-N bond cleavage in 2-azido-1,3-diphenyl-propan-1-one derivatives: photorelease of hydrazoic acid.
abstract: Photolysis of 3-azido-1,3-diphenyl-propan-1-one (1a) in toluene yields 1,3-diphenyl-propen-1-one (2), whereas irradiation of 3-azido-2,2-dimethyl-1,3-diphenyl-propan-1-one (1b) results in the formation of mainly 2,2-dimethyl-1,3-diphenyl-propan-1-one. Laser flash photolysis (308 nm) of 1a,b in acetonitrile reveals a transient absorption (lambda max = approximately 310 nm) due to the formation of radicals 4a and 4b, respectively, which have lifetimes of approximately 14 micros at ambient temperature. TD-DFT calculations (B3LYP/6-31+G(d)) reveal that the first and second excited states of the triplet ketone (T1K (n,pi*) and T2K (pi,pi*)) in azide 1a are almost degenerate, at approximately 74 and 76 kcal/mol above the ground state (S0), respectively. Similarly, azide 1b has T1K and T2K 75 and 82 kcal/mol above S0, respectively. The calculated transition state for cleaving the C-N bond is located 71 and 74 kcal/mol above S0 in azides 1a and 1b, respectively. The calculated bond dissociation energies for breaking the C-N bond are 55 and 58 kcal/mol for azides 1a and 1b, respectively, making C-N bond breakage accessible from T1K in azides 1 at ambient temperature. In comparison, the irradiation of azides 1 in argon matrices at 14 K lead to the formation of the corresponding triplet alkyl nitrenes (1-n), via intramolecular energy transfer from T2K. The characterization of 1-n was supported by isotope labeling, IR spectroscopy, and molecular modeling.
authors.affiliation: Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221-0172, USA.
authors.forename: Rodney F
authors.initials: RF
authors.lastname: Klima
authors.forename: Abhijit V
authors.initials: AV
authors.lastname: Jadhav
authors.forename: Pradeep N D
authors.initials: PN
authors.lastname: Singh
authors.forename: Mingxin
authors.initials: M
authors.lastname: Chang
authors.forename: Christine
authors.initials: C
authors.lastname: Vanos
authors.forename: Jagadis
authors.initials: J
authors.lastname: Sankaranarayanan
authors.forename: Mai
authors.initials: M
authors.lastname: Vu
authors.forename: Nazarin
authors.initials: N
authors.lastname: Ibrahim
authors.forename: Elaine
authors.initials: E
authors.lastname: Ross
authors.forename: Shaun
authors.initials: S
authors.lastname: McCloskey
authors.forename: Rajesh S
authors.initials: RS
authors.lastname: Murthy
authors.forename: Jeanette A
authors.initials: JA
authors.lastname: Krause
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Ault
authors.forename: Anna D
authors.initials: AD
authors.lastname: Gudmundsdóttir
mesh_terms: D001386:Azides / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry / Q000379:methods; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry*; D010777:Photochemistry; D011407:Propane / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D001386:Azides; C007972:hydrazoic acid; D002244:Carbon; D009584:Nitrogen; D011407:Propane