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Note: The … signifies a weak interaction between atoms. Abbreviation: E el , electronic energy. All these topological features confirm the presence of such interaction. All values are in atomic units. In conclusion, quantum chemical calculations showed that the interaction of hydrogen bond donor molecules can modify the S—T gap of alkyl or aryl carbenes.

This interaction may lead to a higher stability of the singlet state over the triplet state by increasing the dipole moment of the former. This increase in dipole moment results in more charge reorganization in the singlet state, rendering them more stable. The most dramatic effect of hydrogen bond formation on the spin state of carbenes is observed for DPC, for which the singlet state becomes the ground state.

Thus, it appears that hydrogen bond-induced spins witch over is applicable to DPCs among the four carbenes considered in this study. This observation is in line with the recent experimental finding of Costa and Sander 19 and Costa et al. The outcome of this study is encouraging in the sense that a single hydrogen bond donor molecule may switch the ground state spin multiplicity of those carbenes with a smaller S—T gap, and thus may prevent their dimerization in solutions of polar solvents.


  • Stable cyclic (alkyl)(amino)carbene (cAAC) radicals with main group substituents.
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Jones M, Moss RA, editors. Vols 1 and 2. Brinker UH, editor.

Advanced in Carbene Chemistry. Vol 1. Vol 2.


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Vol 3. Amsterdam: Elsevier; Reactive Intermediate Chemistry. Hoboken, NJ: Wiley-Interscience; Far infrared laser magnetic resonance of singlet methylene: Singlet—triplet perturbations, singlet—triplet transitions, and the singlet—triplet splitting. J Chem Phys. The singlet—triplet energy separation in silylene.

Radicals and SMILES extensions — Open Babel rc1 documentation

Chem Phys. Multiplicity of the ground state and magnitude of the T1-S0 gap in substituted carbenes. J Am Chem Soc. Persistent triplet carbenes. Chem Rev. Intermolecular effects on intersystem crossing studied on the picosecond timescale: the solvent polarity effect on the rate of singlet-to-triplet intersystem crossing of diphenylcarbene. Picosecond laser studies on the effect of structure and environment on intersystem crossing in aromatic carbenes.

Chem Phys Lett. Effects of solvent polarity and structure on intersystem crossing in diphenylcarbenes. A picosecond laser study on dimesitylcarbene. The dynamics of carbene solvation: an ultrafast study of p -biphenylyltrifluoromethylcarbene.

Study of hydrogen atom abstraction reactions of triplet diphenylcarbene in solution. Carbenes and the oxygen-hydrogen bond: spectroscopic evidence for protonation of diarylcarbenes to give diarylcarbenium ions. Costa P, Sander W.

Radicals and SMILES extensions

Hydrogen bonding switches the spin state of diphenylcarbene from triplet to singlet. Angew Chem Int Ed. The highly reactive benzhydryl cation isolated and stabilized in water ice. Kirmse W. In: Brinker UH, editor. Advances in Carbene Chemistry. Amsterdam: Elsevier Science BV; — Becke AD.

Density-functional thermochemistry. The role of exact exchange.

Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys Rev B Condens Matter. Baer R, Neuhauser D.

Conjugated carbon centered radicals, high-spin systems and carbenes

Density functional theory with correct long-range asymptotic behavior. Phys Rev Lett. Livshits E, Baer R. A well-tempered density functional theory of electrons in molecules. Phys Chem Chem Phys. A density functional theory for symmetric radical cations from bonding to dissociation. J Phys Chem A. A consistent and accurate ab initio parametrization of density functional dispersion correction DFT-D for the 94 elements H-Pu.

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A long-range correction scheme for generalized-gradient-approximation exchange functionals. Zhao Y, Truhlar DG. A new local density functional for main-group thermochemistry, transition metal bonding, thermochemical kinetics, and noncovalent interactions. Quadratic configuration interaction. A general technique for determining electron correlation energies. Neese F. University of Bonn, NWChem: version 6.

Introduction

Comput Phys Commun. Bader RFW. But because hydrogen may be implicit it only does this for atoms which have at least one explicit hydrogen or on atoms which have had ForceNoH called for them - which is effectively zero explicitly hydrogens. Otherwise, atoms with no explicit hydrogen are assumed to have a spin multiplicity of 0, i.

In deciding which atoms should be have spin multiplicity assigned, hydrogen atoms which have an isotope specification D,T or even 1H do not count. Once the spin multiplicity has been set on an atom, the hydrogens can be implicit even if it is a radical. For instance, the following mol file, with explicit hydrogens, is one way of representing the ethyl radical:.

When read by OpenBabel the spinmultiplicity is set to 2 on the C atom 2. If the hydrogens are made implicit, perhaps by the -d option, and the molecule output again, an alternative representation is produced:. OpenBabel will recognize C[O. By default, radical centres are output in explict hydrogen form, e.

C[CH2] for the ethyl radical. All the atoms will be in explict H form, i. OpenBabel supports another SMILES extension for both input and output: the use of lower case atomic symbols to represent radical centres. So the ethyl radical is Cc and the methoxy radical is Co This form is input transparently and can be output by using the -xr option "radicals lower case". It is a useful shorthand in writing radicals, and in many cases is easier to read since the emphasis is on the radical centre rather than the number of hydrogens which is less chemically significant.

In addition, this extension interprets multiple lower case c without ring closure as a conjugated carbon chain, so that cccc is input as 1,3 butadiene. It is interesting that the lower case extension actually improve the chemical representation in a few cases. The latter more accurately represents the symmetry of the molecule caused by delocalisation.

It recognizes c1ccccc1c as the benzyl radical, but it doesn't like c1cc c ccc1. Jump to: navigation , search. Category : Developer. Navigation menu Personal tools Create account Log in. Namespaces Page Discussion.