Graduate Thesis Or Dissertation
 

Intramolecular transfer of complexed radicals as a possible explanation for long-range substituent effects observed in hydrogen abstraction reactions

Public Deposited

Contenu téléchargeable

Télécharger le fichier PDF
https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/tm70mz469

Descriptions

Attribute NameValues
Creator
Abstract
  • The relative rates of hydrogen abstraction from 1-phenylalkanes and a,w-diphenylalkanes using N-bromosuccinimide and bromotrichloromethane were determined at 70°C. In both cases the reactions were photoinitiated. Only benzylic bromination was observed. The 1-phenylalkanes reacted with both reagents to give rates largely independent of substrate. Similarly, the rate of the reaction between the a, w-diphenylalkanes and bromine atom showed little dependence on substrate structure. However, for the reaction of the a, w-diphenylalkanes with trichloromethyl radical, the rates were strongly dependent upon the structure of the substrate. A maximum was found for 1, 6-diphenylhexane. These last results suggest the possibility of hydrogen abstraction by a route where the radical is first complexed with the aromatic ring at one end of the substrate and then intramolecularly transferred to the site of hydrogen abstraction at the opposite end of the substrate. The relative rates of hydrogen abstraction from 4-methyl-1-phenyl-4-(substitutedphenyl)pentanes by trichloromethyl radical were also determined under the same conditions. Application of the Hammett equation yielded a rho value of -0.40 for this reaction. Application of the Taft equation yielded rho values of -1.34 or -1.54 depending upon the Taft substituent constants used. The results for both the Hammett and Taft equations suggest a significant long range substituent effect. To explore the source of this effect, the relative rates of hydrogen abstraction from 4-phenyl-1-substitutedbutanes by trichloromethyl radical were also determined. Application of the Taft equation yielded a rho value of only -0.32. This substituent effect probably arises from inductive interactions between the substituent and the transition state of hydrogen abstraction. The large difference between the Taft rho values obtained for the reaction of the 4-methyl-1-phenyl-4-(substitutedphenyl)pentanes and the 4-phenyl-1-substitutedbutanes with bromotrichloromethane suggest an additional mechanism operative in the former system. A significant amount of that reaction may follow a path where the abstracting radical first forms a pi complex with the substituted phenyl ring of the substrate and then is intramolecularly transferred to the site of hydrogen abstraction.
Resource Type
Date Available
Date Issued
Degree Level
Degree Name
Degree Field
Degree Grantor
Commencement Year
Advisor
Academic Affiliation
Non-Academic Affiliation
Subject
Déclaration de droits
Publisher
Peer Reviewed
Language
Digitization Specifications
  • File scanned at 300 ppi (Monochrome) using ScandAll PRO 1.8.1 on a Fi-6770A in PDF format. CVista PdfCompressor 5.0 was used for pdf compression and textual OCR.
Replaces

Des relations

Parents:

This work has no parents.

Dans Collection:

Articles

La vignette Titre Date de téléchargement Visibilité actes
file details NewkirkDavidD1974.pdf 2017-08-17 Public Télécharger