The Chemical Bond:When Atom Size Instead of Electronegativity Difference Determines Trend in Bond Strength

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Origin of the Captodative Effect: The Lone‐Pair Shielded Radical

Abstract We have quantum chemically analyzed the origin of the captodative effect in the dimerization of para‐substituted phenyl dicyanomethyl radicals RPh(CN)2C⋅ in the gas phase and in solution. Captodative radicals are characterized by the presence of both, electron‐donating and electron‐withdrawing groups, and a weakening of the associated C−C bond in the dimer of these radicals. Our quantitative bonding analyses reveal that the captodative weakening of the C−C bond is the consequence of a special feature in the RPh(CN)2C⋅ electronic structure which we designate “lone‐pair shielded radical”. Solvation effects weaken the C−C bond as the radicals have a more prominent internal charge separation than the dimer and are, therefore, stabilized more than the intact dimer. Interestingly, we find that differences in solvent effects as a function of the para‐substituent in the most prominent case arise from variations in the charge distribution in the dimer, not from that in the separate radicals which experience very similar solvation in those instances

Methyl Substitution Destabilizes Alkyl Radicals

We have quantum chemically investigated how methyl substituents affect the stability of alkyl radicals MemH3−mC⋅ and the corresponding MemH3−mC−X bonds (X = H, CH3, OH; m = 0 – 3) using density functional theory at M06-2X/TZ2P. The state-of-the-art in physical organic chemistry is that alkyl radicals are stabilized upon an increase in their degree of substitution from methyl<primary<secondary<tertiary, and that this is the underlying cause for the decrease in C−H bond strength along this series. Here, we provide evidence that falsifies this model and show that, on the contrary, the MemH3−mC⋅ radical is destabilized with increasing substitution. The reason that the corresponding C−H bond nevertheless becomes weaker is that substitution destabilizes the sterically more congested MemH3−mC−H molecule even more

CCDC 1429114: Experimental Crystal Structure Determination

XAJNEE : bis(μ2-2,4-Di-t-butyl-6-((2-(diphenylphosphino)phenyl)imino)cyclohexa-2,4-dien-1-olato radical)-gold-nickel hexafluorophosphate deuteroacetonitrile solvate Space Group: P b c a (61), Cell: a 15.6769(3)Å b 25.6953(6)Å c 31.0221(6)Å, α 90° β 90° γ 90° Related Article: Daniël L. J. Broere, Dieuwertje K. Modder, Eva Blokker, Maxime A. Siegler and Jarl Ivar van der Vlugt|2016|Angew.Chem.,Int.Ed.|55|2406|doi:10.1002/anie.201509412,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 1429820: Experimental Crystal Structure Determination

XAJNII : Chloro-(2,4-di-t-butyl-6-((2-(diphenylphosphino)phenyl)amino)phenol)-gold(i) chloroform solvate Space Group: P 1 (2), Cell: a 9.6157(4)Å b 9.7984(4)Å c 20.5321(9)Å, α 85.875(2)° β 79.286(2)° γ 63.703(2)° Related Article: Daniël L. J. Broere, Dieuwertje K. Modder, Eva Blokker, Maxime A. Siegler and Jarl Ivar van der Vlugt|2016|Angew.Chem.,Int.Ed.|55|2406|doi:10.1002/anie.201509412,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 1429113: Experimental Crystal Structure Determination

XAJNAA : bis(μ2-2,4-Di-t-butyl-6-((2-(diphenylphosphino)phenyl)imino)cyclohexa-2,4-dien-1-olato radical)-dibromo-di-gold-nickel tetrahydrofuran solvate Space Group: P 21/c (14), Cell: a 13.4429(4)Å b 14.7209(5)Å c 18.3728(5)Å, α 90° β 106.793(3)° γ 90° Related Article: Daniël L. J. Broere, Dieuwertje K. Modder, Eva Blokker, Maxime A. Siegler and Jarl Ivar van der Vlugt|2016|Angew.Chem.,Int.Ed.|55|2406|doi:10.1002/anie.201509412,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 1429112: Experimental Crystal Structure Determination

XAJMUT : bis(μ2-2,4-Di-t-butyl-6-((2-(diphenylphosphino)phenyl)imino)cyclohexa-2,4-dien-1-olato radical)-dichloro-di-gold-nickel dichloromethane solvate Space Group: P 1 (2), Cell: a 9.4197(3)Å b 13.4681(3)Å c 13.5232(3)Å, α 89.3981(19)° β 88.130(2)° γ 71.941(2)° Related Article: Daniël L. J. Broere, Dieuwertje K. Modder, Eva Blokker, Maxime A. Siegler and Jarl Ivar van der Vlugt|2016|Angew.Chem.,Int.Ed.|55|2406|doi:10.1002/anie.201509412,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.