Does Formation of Singlet Propane-1,3-diyl from Propane Deviate from Bond Enthalpy Additivity? Results of Ab Initio Calculations That Bear on the Existence of the Benson Barrier to Diradical Ring Closure

Journal of Physical Chemistry A

Volumn 108, Issue 15, 2004, Pages 3024-3029

  Isborn, Christine ^a   Hrovat, David A ^a   Borden, Weston Thatcher ^a  

^a UNIVERSITY OF WASHINGTON   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

BENSON BARRIER; BOND ENTHALPY ADDITIVITY (BEA); DIRADICAL RING CLOSURE; ENERGY PATHWAYS; HYPERCONJUGATION;

ACTIVATION ENERGY; CHEMICAL BONDS; DISSOCIATION; ENTHALPY; ISOMERIZATION; MOLECULAR STRUCTURE; MOLECULAR VIBRATIONS; QUANTUM THEORY; SPECIFIC HEAT;

PROPANE;

EID: 2342592712     PISSN: 10895639     EISSN: None     Source Type: Journal    
DOI: 10.1021/jp036867b     Document Type: Article

References (40)

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35. Our CISD+Q/cc-pVTZ//(2,2)CASSCF/6-31G* calculations place the (0,0) TS for conrotation of both terminal methylene groups 1.6 kcal/mol lower in energy than the TS for disrotation of both terminal methylene groups and 2.3 kcal/mol lower in energy than the (0,90) TS for rotation of just one methylene.
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38. 2, followed by conrotatory closure of the (0,0)-1 thus formed, results in enantiomerization. However, the same process, but involving either of the C-C bonds to C-3, results in isomerization to the cis isomer.
39. 23 was calculated to reduce the integrated heat capacity of 1, but by only 0.1 kcal/mol.
40. For comparison, at the same level of theory, our calculated BDE at 298 K for butane dissociating to two ethyl radicals is 84.7 kcal/mol. This calculated value is not 5.6, but only 3.3 kcal/mol smaller than the value of BDE = 88.0 ± 0.8 kcal/mol, which is based on the experimental heats of formation of butane and of two ethyl radicals.