Intramolecular environmental effects on the bonding of cyanide and carbonyl

Ultrafast Excited-State Dynamics in Vitamin B12 and Related Cob(III)alamins

“…In cyanide the σ orbital originating from the lone pair electrons on the carbon atom has antibonding character toward the CN bond . Bonding of CN - with a metal tends to reduce this antibonding character and to increase the CN stretching frequency.…”

Mechanistic Aspects of Gas‐Phase Hydrogen‐Atom Transfer from Methane to [CO].+ and [SiO].+: Why Do They Differ?

“…As described previously, [34] adding a proton or a point charge to the carbon (oxygen) atom of CO results in a shortening (or an elongation) of the CÀO bond, that is, the higher stability of [HCO] + versus [COH] + can be traced back in part to the stronger C À O bond in the former species. The strengthening of the C À O bond upon protonation at the carbon atom of CO has previously been assigned to an antibonding character of the 5s orbital of CO that is located at the carbon atom and forms the bond to the proton; [35] however, according to more recent studies the strengthening is due mostly to an electrostatic effect: [34] the bonding orbitals in free CO are polarized towards oxygen, and adding a proton at the C atom is expected to oppose this polarization and thus to enhance the covalent character of the CO bond. The approach of methane at the O site of [CO]C + triggers a so-called intramolecular spin-density transfer [11c] and leads to the barrier-free transfer of the hydrogen to the oxygen atom; in the process 1!3, OÀH bond formation occurs at the expense of weakening the CÀO bond.…”

“…: 1.115 [33] ) for [CO]C + . The strengthening of the C À O bond upon protonation at the carbon atom of CO has previously been assigned to an antibonding character of the 5s orbital of CO that is located at the carbon atom and forms the bond to the proton; [35] however, according to more recent studies the strengthening is due mostly to an electrostatic effect: [34] the bonding orbitals in free CO are polarized towards oxygen, and adding a proton at the C atom is expected to oppose this polarization and thus to enhance the covalent character of the CO bond. The strengthening of the C À O bond upon protonation at the carbon atom of CO has previously been assigned to an antibonding character of the 5s orbital of CO that is located at the carbon atom and forms the bond to the proton; [35] however, according to more recent studies the strengthening is due mostly to an electrostatic effect: [34] the bonding orbitals in free CO are polarized towards oxygen, and adding a proton at the C atom is expected to oppose this polarization and thus to enhance the covalent character of the CO bond.…”

Fe L-Edge XAS Studies of K4[Fe(CN)6] and K3[Fe(CN)6]: A Direct Probe of Back-Bonding

“…23 It was first understood experimentally, 21 and later shown with molecular orbital (MO) calculations, that both the 5σ + occupied and 2π* unoccupied orbitals are antibonding with respect to the CN -bond. 24,25 This means that σ donation has the effect of shortening the C-N distance, whereas π backdonation lengthens it. From this relationship, periodic trends in the bonding to transition metals could be observed based on vibrational frequencies.…”

“…Around the same time as the absorption spectra were investigated, substantial research focused on the force constants of metal−carbon and carbon−nitrogen bonds. − These were also interpreted in terms of σ donation and π back- donation . It was first understood experimentally, and later shown with molecular orbital (MO) calculations, that both the 5σ + occupied and 2π* unoccupied orbitals are antibonding with respect to the CN - bond. , This means that σ donation has the effect of shortening the C−N distance, whereas π back-donation lengthens it. From this relationship, periodic trends in the bonding to transition metals could be observed based on vibrational frequencies. , It was found that [Fe(CN) 6 ] 4- has a lower CN - force constant than [Fe(CN) 6 ] 3- .…”