And MO calculations

Both experimental studies on gas-phase ion stability and MO calculations indicate that the two vinyl cations shown below benefit fiom special stabilization. Indicate what stmctural features present in these cations can provide this stabilization. 

Structural data from X-ray- and electron-diffraction studies, mass spectra, and MO calculations were analyzed for R3SiCo(CO)4 (R = H, F, Cl) and Me3SiMn(CO)5 it was believed that there is partial double-bond character between Si and Co and that there may be intramolecular interaction between the axial silicon atom and the equatorial carbonyl groups 30, 212). 

Trends in J(P1SN) and 615 N for a series of triphenyl-phospha(A )azenes (33) were used with 1 3C and 31 P n.m.r. data, cyclic voltametry and MO calculations to evaluate the nature of the bonding to phosphorus.79 Diphosphorylamides (34) ° and a diazaphosphorin dithione 1 was also studied by SN n.m.r. spectroscopy ... 

The in vitro trypanocidal and antitumor activities of lfr(cot)L], cot = cyclotetraene, derivatives of dithiocarbamates and xanthates, have been investigated.700 The Ir complexes were characterized by IR spectroscopy, and MO calculations (Hiickel) were performed on the ligands. Similar studies were performed on [Ir(nbr)L], nbr = norbornadiene, L = derivatives of alquil and aryl xanthates 701 and also on [Ir2(cod)2L]X2, where L = 2-hydroxystilbamidine, X = C1, N03, C104, BPh4, and [Ir(cod)L2 ]X, where L = benznidazole, R0-2516, nifurtimox, niridazole. The complex [Ir2(cod)2(2-hydroxystilbami-dine)](BPh4)2 showed the highest activity, as studied by optical microscopy of rats kidneys. 

Our understanding of the physicochemical properties of pyrazines has deepened. The internal rotation and IR spectrum of 2,5-pyrazinedicarboxamide were studied by quantum chemical calculations <05TC73>, and ab initio MO calculations at the MP2/6-31++G( ) level were used to explain the electronic and vibrational properties of complexes of pyrazine and HX linear acids <05JMS2822>. MM and MO calculations were used to investigate the conformational and electronic properties of odor-active pyrazines <05JMS169>, and NMR, IR, X-ray, and DFT methods were used to examine the structures of pyridol l,2-a pyrazinium bromide <05JMS7>. 

The hexacarbaborane 76 (Scheme 3.2-40) has a drum-shaped arachno-C6B6 structure, according to NMR data and MO calculations. It is assumed that 76 results from further condensation of 67 with 68 to give the intermediate 77. Interestingly, the compound 78 is the parent compound of 76, however, they have different structures. 78 is a C4B6-cluster having a classical C2H2 handle [98]. 

Fig. 19 n-Spin-density distribution in diphenylcarbene [15 m= ] determined by ENDOR experiments and MO calculations. The o-spin density at the divalent carbon is in parentheses. 

Anions (9), (10a) and (11) derived from cycloctatetraene have been studied using the selected ion flow tube technique and MO calculations, as a continuation of previous work on the structures and energetics of eight-membered-ring species, CgH and... 

According to ESR spectra and MO calculations for these anion-radicals, the unpaired electron is indeed associated with the nitrogen-nitrogen n orbital (Bushby and Ng 1996). 

In comparison with hydrocarbons, aromatic amines easily transform into cation radicals. Structures of these cation radicals are well documented on the basis of their ESR spectra and MO calculations (see, e.g., Grampp et al. 2005). The stable cation radical of A/,A,A, A -tetramethyl-p-phenylenediamine (the so-called Wuerster s blue) was one of the first ion radicals that was studied by ESR spectroscopy (Weissmann et al. 1953). The use of this cation radical as a spin-containing unit for high-spin molecules has been reported (Ito et al. 1999). Chemical oxidation of N,N -bis [4-(dimethylamino)-phenyl-A/,A -dimethyl-l,3-phenylenediamine with thianthrenium perchlorate in -butyronitrile in the presence of trifluoroacetic acid at 78°C led to the formation of the dication diradical depicted in Scheme 3.58. 

ASOa-perovskites of Table 6 extends from Dza through Can to Ci. Distinct band-splittings are not observed, however, 13) (Fig. 2). As is demonstrated for the YCra Ali-a 03-system, the Oo-transition is situated at 13600 to 13700 cm i independent of the Cr3+ concentration (Fig. 2) leading to a B55 of 705 cm (Table 3), which is more than 5% lower than for the corundum and spinel compounds discussed. This is in agreement with the possibility of relatively strong Ji-bonds in the perovskite structure, which could be inferred from spectroscopic and crystallographic results 3) as well as from NMR-data and MO-calculations 33) for Ni2+,... 

Amides and related compounds have been thoroughly investigated as ligands for alkali metals. Studies in solution have been made using various physicochemical techniques these, and MO calculations, show that the interaction of amides with M+ is via the carbonyl function.56,57 This leads to a delocalization of the amide N electron pair and so it is possible to follow the decrease in C—O, and the increase in C—N, bond orders using IR spectroscopy. X-Ray crystal structures of amide complexes have shown both types of complexation interaction to be present (Table 2). 

In the requisite DAh geometry the constituents of the metal-metal quadruple bond comprise a a bond of axg symmetry, formed by the linear union of dz j AOs, a it bond of eu symmetry, which results from the end-to-end overlap of dxz and dyz AOs, and the 8 bond of b2g symmetry, which arises from the face-to-face interaction of eclipsed dxy AOs. When the ligands are considered many additional interactions take place and MO calculations must be used to delineate a cogent MO scheme. For the parent tetracarboxylate, Mo2(02CH)4,... 

Unlike the Rh-based hydrogenation of a-(acylamino)acrylates, the corresponding Ru chemistry has not been studied extensively. Ru complexes of (S)-BINAP and (S,S)-CHIRAPHOS catalyze the hydrogenation of (Z)-a-(acylamino)cinnamates to give the protected ( -phenylalanine with 92% ee [74] and 97% ee [75], respectively. It is interesting that the Rh and Ru complexes with the same chiral diphosphines exhibit an opposite sense of asymmetric induction (Scheme 1.6) [13,15,56,74,75]. This condition is due primarily to the difference in the mechanisms the Rh-catalyzed hydrogenation proceeds via Rh dihydride species [76], whereas the Ru-catalyzed reaction takes place via Ru monohydride intermediate [77]. The Rh-catalyzed reaction has been studied in more detail by kinetic measurement [78], isotope tracer experiments [79], NMR studies [80], and MO calculations [81]. The stereochemical outcome is understandable by considering the thermodynamic stability and reactivity of the catalyst-enamide complexes. 

Huge amount of studies by means of molecular orbital (MO) calculations have been reported in the literature, which calculate the structures of reactants, products, reactive intermediates, and TSs of possible reaction pathways, as well as minimum energy paths from the TSs to both the reactant and product sides on the potential energy surface (PES). The information thus obtained, together with experimental findings, has been used to deduce reaction mechanisms. The combined use of experiment and MO calculations has become a common method for physical organic chemists. However, it should be noted that the calculated structures and energies are at OK and that therefore the information obtained from MO calculations may not directly be related to experimental observation at a finite temperature. 

Apparently, a similar valence bond picture holds true for 4-alkylidene pyrazoline anion radicals. These radicals were prepared by reducing (potassium mirror in DME) of the pyrazolines depicted in Scheme 3-13. According to ESR spectra and MO calculations for these anion radicals, the unpaired electron is indeed associated with the nitrogen-nitrogen ir -orbital (Bushby Ng 1996). 

Methods based on molecular graphics, molecular mechanics, molecular dynamics, and MO calculations, used for the design of new compounds. CAMD is not equivalent to molecular modeling but rather a subdiscipline of it (see molecular modeling, molecular mechanics, molecular dynamics). 

Here, we propose a ground state structure of CV other than the D3-symmetry and the C2-symmetry based on the experimental observations and MO calculations of our own as well as the previous studies. This proposed structure comprehensively explains all the current and previous experimental observations and theoretical calculations. 

The rates of reaction of triplet nitrenes and carbenes were compared by DFT and MO calculations.76 Triplet nitrenes are more stable than the analogous carbene and CO bonds stronger than NO bonds the two effects are nearly additive in the reaction of nitrenes and carbenes with molecular oxygen. 

Single-crystal e.p.r. studies and MO calculations on several vanadium complexes389 indicate that the highest occupied MO has substantial (50—70%) 3dzi character and very little 3dxi y2 or 4s. This is entirely compatible with the observed decrease of ca. 6° in the L—M—L bond angle which occurs on occupation of this orbital i.e. on going from TiIV, d° to Viv, dl. 

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