Nitrogen molecular orbitals

R. Gleiter, Stmcture and Bonding in Cyclic Sulfur-Nitrogen Compounds Molecular Orbital Considerations, Angew. Chem. Int. Ed. Engl., 20, 444 (1981). 

Unlike reactive diatomic chalcogen-nitrogen species NE (E = S, Se) (Section 5.2.1), the prototypical chalcogenonitrosyls HNE (E = S, Se) have not been characterized spectroscopically, although HNS has been trapped as a bridging ligand in the complex (HNS)Fc2(CO)6 (Section 7.4). Ab initio molecular orbital calculations at the self-consistent field level, with inclusion of electron correlation, reveal that HNS is ca. 23 kcal mof more stable than the isomer NSH. There is no low-lying barrier that would allow thermal isomerization of HNS to occur in preference to dissociation into H -1- NS. The most common form of HNS is the cyclic tetramer (HNS)4 (Section 6.2.1). 

Examine the highest-occupied molecular orbital (HOMO of cyanide anion. Is the larger lobe on carbon or nitrogen Would you expect cyanide to act as a carbon or nitrogei nucleophile Does this lead to the lower energy transitioi state (compare the energy of cyanide-l-methyl iodide ( attack and cyanide+methyl iodide N attack) ... 

Molecular orbital based molecular mechanical (MOMM) calculations have been carried out on 3H-2-benzazepinyl phosphonates.43 Similar calculations on 5//-dibenz[Z>,/]azepine lead to the prediction that there are two stable boat conformations for the seven-membered ring both of which are more stable than the planar form by 22.6 and 10.9 kJ moP, respectively the more stable conformer being the one in which the proton on nitrogen is exo lo the azepine... 

Structures considered are quinolizinium (187), and 1,5- (188), 1,6- (189), 1,7- (190), 1,8- (191), and 2,7- (192) naphthyridines. In the naphthyridines the 10 7r-electrons are delocalized in five bonding molecular orbitals, which are distorted by the annular nitrogens in such a way that positions ortho and para to those nitrogens are less likely to be electrophilically haloge-nated than meta carbons. Compounds with a nitrogen at the ring junction carry a positive charge and will be naturally resistant to electrophilic attack. 

The facile thermal decomposition of the dimethyl and diethyl derivatives of (II) to nitrogen and carbene intermediates is emphasized by the readily discernible correlations between the reactant and product orbitals. On the other hand, the greater delocalization of the molecular orbitals of (I) may be a factor in its preference to rearrange, without decomposition, to methyl acetylene and allene. 

Tsuda and Oikawa (1989) investigated the photolysis of the 1,2-isomer of 10.89 (1,2-benzoquinone diazide) by means of MINDO/3 molecular orbital calculations with configurational interaction. These authors came to the conclusion that no ketocarbene of the type of 10.90 is formed, but that the rearrangement into the cyclopentadienyl ketene 10.94 is a concerted reaction in which the elimination of nitrogen and the rearrangement take place simultaneously. In the opinion of the present author the theoretical result for 1,2-quinone diazide is not necessarily in contradiction to the experimental investigations of Sander, Yankelevich et al., and Nakamura et al., as the reagents used were not exactly the same. 

The photoelectron spectrum of nitrogen (N2) has several peaks, a pattern indicating that electrons can be found in several energy levels in the molecule. Each main group of lines corresponds to the energy of a molecular orbital. The additional "fine structure" on some of the groups of lines is due to the excitation of molecular vibration when an electron is expelled. 

Draw simple molecular orbital energy-level diagrams to indicate how the bonding in the saline hydrides, such as NaH or KH, differs from that between hydrogen and a light p-block element such as carbon or nitrogen. 

---