Schleyer P, Clark T (1991)
Publication Status: Published
Publication Type: Journal article
Publication year: 1991
Publisher: American Chemical Society
Book Volume: 113
Pages Range: 2466-2471
Journal Issue: 7
DOI: 10.1021/ja00007a018
Degenerate 1,3-BR2-shifts in allylboranes (R = alkyl) are shown by ab initio molecular orbital theory to proceed through a nonplanar transition structure with C(s) symmetry. The MP2/6-31G*//6-31G* + ZPE barrier of 9.2 kcal/mol for dimethylallylborane agrees with experimental values. However, the corresponding bridged structure (2) is the most stable form of the parent allylborane, CH2=CHCH2BH2 at MP2/6-31G*//MP2/6-31G* + ZPE. The unsymmetrical open conformation (1), which prefers C1 symmetry, is only 0.1 kcal/mol higher in energy. Other structures on the C3BH7 potential energy surface are also comparable in energy. Like the isoelectronic cyclobutyl cation (bicyclobutonium ion), the four-membered boron heterocycle boretane (3a) prefers a nonplanar structure (C(s) symmetry). Another small ring isomer, cyclopropylborane with a bisected geometry, 4a, is only 1.2 kcal/mol higher in energy than 1. The calculated (IGLO) chemical shifts of the isomers are discussed. The boron nucleus in the symmetrically bridged allylborane 2 is calculated to be strongly shielded (-49 ppm), whereas borons incorporated in small ring systems are predicted to be deshielded (e.g, 93 ppm for 5 and 97 ppm for planar 3b). The rotation barriers in vinylborane and dimethylvinylborane are 6.9 and 4.0 kcal/mol, respectively.
APA:
Schleyer, P., & Clark, T. (1991). ALLYLBORANE AND ITS ISOMERS - AN ABINITIO STUDY OF THE C3BH7 POTENTIAL-ENERGY SURFACE, THE BARRIER TO 1,3-SHIFTS IN ALLYLBORANES, AND NONCLASSICAL BORACYCLOBUTANE, CYCLOPROPYLBORANE, AND VINYLBORANE STRUCTURES. Journal of the American Chemical Society, 113(7), 2466-2471. https://dx.doi.org/10.1021/ja00007a018
MLA:
Schleyer, Paul, and Timothy Clark. "ALLYLBORANE AND ITS ISOMERS - AN ABINITIO STUDY OF THE C3BH7 POTENTIAL-ENERGY SURFACE, THE BARRIER TO 1,3-SHIFTS IN ALLYLBORANES, AND NONCLASSICAL BORACYCLOBUTANE, CYCLOPROPYLBORANE, AND VINYLBORANE STRUCTURES." Journal of the American Chemical Society 113.7 (1991): 2466-2471.
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