Topic
Steric effects
About: Steric effects is a research topic. Over the lifetime, 16112 publications have been published within this topic receiving 319615 citations. The topic is also known as: steric hindrance.
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104 citations
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TL;DR: In this article, the potential energy barrier to internal methyl rotation and the preferred methyl conformation depend on the position of the fluorine, amino, or methyl substituents and also on the electronic state, either S0, S1, or ground state cation.
Abstract: In substituted toluenes, the potential energy barrier to internal methyl rotation and the preferred methyl conformation depend on the position of the fluorine, amino, or methyl substituents and also on the electronic state, either S0, S1, or ground state cation. We present a unified picture of the electronic factors controlling these effects. In S0 and cation, ab initio electronic structure calculations of modest scale produce rotor potentials in good agreement with experiment. The methyl group provides a sensitive probe of local ring geometry. When the geometry of the ring in the vicinity of the rotor has good local C2v symmetry, the barrier is invariably small. In S0 ortho‐substituted toluenes, we use natural steric analysis to show that repulsive steric interactions between the halogen lone pair and the methyl CH bonds dominate over attractive donor–acceptor interactions to favor the pseudo‐trans conformation. When steric interactions are unimportant, the key determinant of rotor barrier height is the ...
104 citations
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TL;DR: It is somewhat surprised to find that an adduct is readily formed simply upon mixing 1 with the 9-BBN bistriflimide reagent 5a despite the transannular steric demands of the 9 -BBN core and the need to form adjacent quaternary bonds to boron as well as nitrogen.
Abstract: During our studies on aromatic borylation,[1] we considered the combination of a highly electrophilic R2BNTf2 reagent with a base that would neutralize the HNTf2 byproduct of borylation without deactivating the electrophile. In principle, these requirements might be satisfied by 1,8-bis(dimethylamino)naphthalene (1), a hindered and exceptionally basic aniline that finds numerous applications as a basic catalyst or reagent due to its legendary lack of nucleophilicity.[2, 3] Strong electrophiles interact weakly, if at all, with the amine nitrogens, and very few examples are known where stable bonds to nitrogen can be formed between 1 and electrophilic groups larger than hydrogen.[2, 4-7] Among these exceptional cases, cyclic boronium structures 2 and 3 are relatively stable because the subunits BH2 and BF2 have minimal steric requirements.[5] However, the more hindered BMe2 derivative 4 has not been detected and no analogous BR2 structures are known.[5a, 8] In view of this long history, we were somewhat surprised to find that an adduct is readily formed simply upon mixing 1 with the 9-BBN bistriflimide reagent 5a despite the transannular steric demands of the 9-BBN core and the need to form adjacent quaternary bonds to boron as well as nitrogen.[9, 10] The remarkable structural features and unusual reactivity of this adduct are the subject of the following communication.
104 citations
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TL;DR: In this paper, the authors describe the results obtained by their group on the synthesis of metallic thiolato complexes by the electrochemical oxidation of a sacrificial anode in a non-aqueous solution of the precursor ligand.
104 citations
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TL;DR: Some aspects of the HeI photoelectron spectroscopy of substituted phenylethylenes and related molecules are presented in this article, where the interpretation of the variation of the photo-electron π ionization energies with substituents allows the separation of steric from electronic effects.
Abstract: Some aspects of the HeI photoelectron spectroscopy of substituted phenylethylenes and related molecules are presented. The interpretation of the variation of the photoelectron π ionization energies with substituents allows the separation of steric from electronic effects. Interaction of semi-localised π molecular orbitals incorporated within a Huckel type theory provides a means of estimation of the dihedral angles.
103 citations