Photodissociation of N-(triphenylmethyl)anilines: A laser flash photolysis, ESR, and product analysis study
Φόρτωση...
Ημερομηνία
Συγγραφείς
Siskos, M. G.
Zarkadis, A. K.
Steenken, S.
Karakostas, N.
Garas, S. K.
Τίτλος Εφημερίδας
Περιοδικό ISSN
Τίτλος τόμου
Εκδότης
American Chemical Society
Περίληψη
Τύπος
Είδος δημοσίευσης σε συνέδριο
Είδος περιοδικού
peer reviewed
Είδος εκπαιδευτικού υλικού
Όνομα συνεδρίου
Όνομα περιοδικού
Journal of Organic Chemistry
Όνομα βιβλίου
Σειρά βιβλίου
Έκδοση βιβλίου
Συμπληρωματικός/δευτερεύων τίτλος
Περιγραφή
N-(Triphenylmethyl)anilines (Ph3C-NHPh-R, R = H, o-Me, m-Me, p-Me, p-CPh3), upon photolysis with 248- and 308-nm laser light, as well as by lamp irradiation with 254-nm light in acetonitrile and hexane solutions, undergo exclusively C-N bond homolysis to give the triphenylmethyl radical in a monophotonic process. Product analysis gives as main products Ph3CH, 9-Ph-fluorene, and PhNH2. The quantum yields for the formation of Ph3C. are high (0.6-0.8, 248-nm excitation) and independent of the solvent. This effective homolytic dissociation results from the low electronegativity difference between the carbon and nitrogen atoms constituting the bond to be broken, the low bond dissociation enthalpy of the C-N bond, the high excitation energy of the local chromophore (aniline), and probably from a favorable alignment of the C-N bond in a plane perpendicular to the anilino chromophore (due to the large steric requirements of the trityl group), thus enabling an effective hyperconjugative interaction with it. The above dissociation competes effectively with heterolytic cleavage, which is the pathway dominating, e.g., in the photolysis of Ph3C-Cl in MeCN under the same conditions. At high pulse intensities the trityl radicals formed above are excited by a second photon leading to either electrocyclization to 4a,4b-dihydro-9-phenylfluorenyl radical (DHPF.), or photoionization to PhaC(+), the latter only in MeCN and only on 248-nm photolysis. A new intermediate (9-Ph-4aH-fluorene) on the way to the final product 9-Ph-fluorene is identified resulting from electrocyclization, supporting a mechanism proposed earlier. The optical measurements are supported by ESR studies (irradiation with 254-nm light).
Περιγραφή
Λέξεις-κλειδιά
bond-dissociation energies, contact ion-pairs, excited diphenylmethyl radicals, photoinduced electron-transfer, stable free-radicals, picosecond dynamics, arylmethyl radicals, aqueous-solution, triphenylmethyl radicals, bimolecular formation
Θεματική κατηγορία
Παραπομπή
Σύνδεσμος
<Go to ISI>://000073769600019
http://pubs.acs.org/doi/pdfplus/10.1021/jo9719261
http://pubs.acs.org/doi/pdfplus/10.1021/jo9719261
Γλώσσα
en
Εκδίδον τμήμα/τομέας
Όνομα επιβλέποντος
Εξεταστική επιτροπή
Γενική Περιγραφή / Σχόλια
Ίδρυμα και Σχολή/Τμήμα του υποβάλλοντος
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας