EPR data do not indicate that hyperconjugation stabilizes alkyl radicals

Organic Letters

Volumn 9, Issue 11, 2007, Pages 2211-2214

  Gronert, Scott ^a  

^a VIRGINIA COMMONWEALTH UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 34250614314     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol070706z     Document Type: Article

References (29)

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8. The plot in Figure 1 is slightly different than that presented by Ingold and DiLabio. Here, BDE's from Blanksby and Ellison have been used (see ref 9). Ingold and DiLabio do not state the origin of their BDE's. The values for the alkanes match those of Blanksby and Ellison, but the value for propene that they used differs by nearly 3 kcal/mol from the Blanksby and Ellison value. The important effect is that now the 32%/62% spin polarization/hyperconjugation model in Figure 1 of the Ingold/DiLabio paper gives a better fit than the proposed 45%/55% model.
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24. The evidence for repulsive 1,3 interactions is derived from a variety of experiments from different research groups that were designed to specifically probe this interaction. These experiments have consistently indicated that they are repulsive. In contrast, the effect of branching on alkane heats of formation involves a multitude of structural changes along with the development of 1,3 carbon-carbon interactions. For example, the isomerization from butane to isobutane involves a shift from a system with six 1° C-H bonds and four 2° C-H bonds to a system with nine 1° C-H bonds and one 3° C-H bond. In the absence of independent, supporting data, it is a wholly arbitrary decision to assign the energy change specifically to the development of more methyl/methyl 1,3 interactions in the branched alkanes.
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