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Steric trends and kinetic parameters for radical reductions involving alkyldiphenyltin hydrides
Author(s) -
Dakternieks Dainis,
Henry David J.,
Schiesser Carl H.
Publication year - 1999
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199903)12:3<233::aid-poc117>3.0.co;2-t
Subject(s) - chemistry , steric effects , reactivity (psychology) , arrhenius equation , hydride , reaction rate constant , hydrogen atom abstraction , radical , trimethylsilyl , substituent , medicinal chemistry , hydrogen atom , alkyl , hydrogen , photochemistry , tributyltin hydride , computational chemistry , activation energy , stereochemistry , kinetics , organic chemistry , medicine , alternative medicine , physics , pathology , quantum mechanics
Absolute rate constants and Arrhenius parameters for hydrogen atom abstraction by primary alkyl radicals from methyldiphenyl‐, ethyldiphenyl‐, butyldiphenyl‐, iso propyldiphenyl‐, cyclohexyldiphenyl‐ and (trimethylsilyl)methyldiphenyltin hydride were determined in tert ‐butylbenzene through utilization of the ‘5‐hexenyl radical clock’ reaction. At 80 °C, rate constants ( k H ) for all hydrides were found to lie in the range (8.2–11.5) × 10 6 lmol −1 s −1 , with similar Arrhenius expressions for all reactions studied [viz. log k H = (8.92–8.97)−(3.03–3.24)/2.3 R T]. The nature of the alkyl substituent appears to have a subtle effect on the function of the hydride such that the order or reactivity of stannanes (RPh 2 SnH) is Me > Et > Bu > i ‐Pr > c ‐Hex ≥ Me 3 SiCH 2 ; this trend can be directly traced to steric effects operating in the transition states for hydrogen transfer from tin to carbon. The implications of these observations are discussed. Copyright © 1999 John Wiley & Sons, Ltd.