Carbon-nitrogen bonds comparisons

Petrongolo C, Pescatori E, Ranghino G, Scordamaglia R. Ab initio study of P-lactam antibiotics. II. Potential energy surface for the amidic carbon-nitrogen bond breaking in the 3-cephem+hydroxide ion reaction and comparison with the P-lactam+hydroxide ion reaction. Chem Phys 1980 45 291-304. 

One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(ll) carbene to an Fe(lll) complex where the vinylidene carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment formally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron, has been considered in a theoretical study. The comparison is especially interesting for the iron(ll) and cobalt(lll) carbene complexes Fe(Por)CR2 and Co(Por)(CR2) which both contain metal centers yet adopt... 

Fry and Newberg 1,2> examined the electrochemical reduction of nor-camphor oxime (109) and camphor oxime (110) to the corresponding amines. The results of this study are shown in Table 3. It is clear from a comparison of these data with those in Table 2 that the electrochemical reduction of oximes 109 and 110 takes a very different stereochemical course from reduction of the corresponding anils 103 and 104. Reduction of oximes apparently proceeds under kinetic control, affords products corresponding to protonation at carbon from the less hindered side of the carbon-nitrogen double bond, and affords the less stable epimeric amine in each case. It is not evident why the stereochemistry of reduction of anils and oximes should differ, however. 

There is considerable multiple character in the carbene carbon-X(Y) bonds. An internal comparison of carbon-X(Y) bond lengths in each of the structures tabulated reveals a substantial shortening of carbene car-bon-X(Y) relative to other carbon-X(Y) bonds in the molecule. Carbene carbon-nitrogen distances are found to be shorter in the mono-N-substituted carbenes than in the bis-N-substituted compounds. 

The tertiary enamines, in contrast to the secondary derivatives, cannot exhibit enamine-imine tautomerism. As the free bases, they exist only in the vinylamino form. Their physico-chemical properties are in agreement with this structure, especially the spectral properties. The bands due to the stretching frequency of the carbon-carbon double bond in their infrared spectra1-25-27 (situated at 1630-1660 cm-1 according to the nature of the substituents) occur at somewhat lower frequencies, but their intensities are greatly increased in comparison to those of simple olefins because of conjugation with the free electron pair on the nitrogen atom. Indications of cis-trans isomerism... 

Roesky introduced bis(iminophosphorano)methanides to rare earth chemistry with a comprehensive study of trivalent rare earth bis(imino-phosphorano)methanide dichlorides by the synthesis of samarium (51), dysprosium (52), erbium (53), ytterbium (54), lutetium (55), and yttrium (56) derivatives.37 Complexes 51-56 were prepared from the corresponding anhydrous rare earth trichlorides and 7 in THF and 51 and 56 were further derivatised with two equivalents of potassium diphenylamide to produce 57 and 58, respectively.37 Additionally, treatment of 51, 53, and 56 with two equivalents of sodium cyclopentadienyl resulted in the formation of the bis(cyclopentadienly) derivatives 59-61.38 In 51-61 a metal-methanide bond was observed in the solid state, and for 56 this was shown to persist in solution by 13C NMR spectroscopy (8Ch 17.6 ppm, JYc = 3.6 2/py = 89.1 Hz). However, for 61 the NMR data suggested the yttrium-carbon bond was lost in solution. DFT calculations supported the presence of an yttrium-methanide contact in 56 with a calculated shared electron number (SEN) of 0.40 for the yttrium-carbon bond in a monomeric gas phase model of 56 for comparison, the yttrium-nitrogen bond SEN was calculated to be 0.41. 

N2 itself, with a triple bond between the two atoms, is strikingly unreactive. In comparison to CO, N2 is a nonpolar molecule that has lone electron pairs on nitrogen atoms. The general unreactivity of Nj molecule, its non-polarity, and lone pairs on more electronegative nitrogen (in comparison to carbon of CO) make N2 a very weak ligand that does not bind to haemoglobin. Consequently N2 molecule is not toxic. 

Table 8-6. Comparison of Nitrogen Fluoride and Carbon Fluoride Bond Energies...

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