Structural and Spectroscopic Studies

HF/6-31G calculations have been used to identify the thermodynamic products of the reaction of AlMes and aromatic ketones. The reaction between AlMes with 2,4,6-trimethylacetophenone favours enolisation over alkylation by ca. 20 kJ moG The reaction between AlMes and acetophenone, however, favours alkylation to form an alkoxide by ca. 106 kJ mol . Methyl substitutents on the phenyl ring lead to relative destabilisation of the alkoxide by steric crowding. 

PM 3 calculations have been performed on the series of indium methylene compounds BrsInCHaEPhs with Group 15 donors E = P, As and Bi. The results suggest an ylide-type ligand for the In compounds with C -E.  

B3LYP/DZP calculations of the structural, vibrational frequencies and stability of the donor-acceptor complexes RsGaNR s, the products of their dissociation GaR , NR -, and the products of their association R2GaNR 2 and RGaNR (R, R = H, CH3, n = 1-3) have been reported. Elimination of RR from the complexes followed by association is thermodynamically favoured. 

The conformers and vibrational spectra of vinyldichlorosilane have been studied at the MP2/6-311-1- G(2d,2p) level. The gauche form is predicted to be more stable than the cis conformer by ca. 0.2 kJ mol with smaller basis sets predicting the cis conformation to be more stable. 

The structures and conformations of cyclic and polycyclic silthianes containing Si-Si bonds have been studied at the B3LYP/6-31G level. The most stable structures contain SisS2 rings with Si-S-Si-S-Si- connectivity. 

The molecular structures and bonding of [M(R)(CO)5] species (M = Mn, Tc, Re R = alkyl) have received considerable attention over the years, mainly because they contain a simple cr bond between a transition metal and an alkyl group. The structures of the methyl compounds [Mn(CH3)(CO)s] and [Re(CH3)(CO)5] have been investigated by a wide variety of techniques, including X-ray, electron, and incoherent inelastic neutron diffraction, as well as spectroscopic techniques, namely, vibrational, NMR, and mass spectroscopy. Several theoretical studies have also been reported. 

A problem arose when the X-ray crystal structure of [Mn(CH3)(CO)5] was attempted (55). Results showed that the solid phase was almost entirely orientationally disordered each of the six coordination sites around the manganese atom was found to be occupied by, on average, about five-sixths of a carbonyl ligand and one-sixth of a methyl ligand. The superimposed methyl and carbonyl carbon atoms could not be resolved, which precluded determination of any significant bonding parameters. However, the X-ray diffraction data did indicate that [Mn(CH3)(CO)5] crystallizes in 

Several photoelectron spectroscopy (PES) studies on [M(R)(CO)j] (M = Mn, Re) have been reported (54-60). However, it is beyond the scope of this article to cover each of these reports in detail hence, we mention only a few of the most relevant and recent results. 

The above two studies concluded that internal rotation of the methyl group in [Mn(CH3)(CO)s] is essentially free, with the C-H stretching frequency showing a slight dependence on orientation. However, these conclusions were based on measurement of infrared bands with no resolution of rotational structure, and this limited the information available. High-resolution infrared studies by Gang et al. (66) confirmed that any restriction of rotation of the methyl group was below the limit of detection by this method. 

Calderazzo et al. (68) have measured Mn NMR spectra for various [Mn(R)(CO)5] compounds and found the chemical shift (in ppm) to increase as the electron-donating ability of R increased. Webb and Graham (69) have reported C NMR data for some [Re(R)(CO)s] compounds which showed that the carbonyl carbon atoms trans to R are more shielded than those cis to R. When compared to C NMR data known for [Mn(R)(CO)5] species (70), it appears that the generally observed increase in shielding of carbonyl carbon atoms on descending a periodic group (for transition metals) is in evidence for manganese and rhenium. 

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Early work established that S4N4 forms di-adducts with alkenes such as norbornene or norbomadiene. Subsequently, structural and spectroscopic studies established that cycloaddition occurs in a 1,3-S,S"-fashion. The regiochemistry of addition can be rationalized in frontier orbital terms the interaction of the alkene HOMO with the low-lying LUMO of S4N4 exerts kinetic control. Consistently, only electron-rich alkenes add to S4N4. 

Duffy NW, Lane DW, Ozsan ME, Peter LM, Rogers KD, Wang RL (2000) Structural and spectroscopic studies of CdS/CdTe heterojunction cells fabricated by electrodeposition. Thin Sohd Films 361 314-320... 

Recently we investigated ferromagnetic properties of CoPt bimetallic nanoparticles [232,233]. CoPt3 nanoparticles can be prepared by a two-step reduction using NaBH4 as a reductant. The bimetallic nanoparticles were characterized by thermogravimetry (TG) and differential thermal analysis (DTA), FT-IR, TEM) and XRD. Structural and spectroscopic studies showed that the bimetallic nanoparticles adopt an fee crystalline structure with an average particle size of 2.6 nm. SQUID studies revealed... 

Stabilization of quinone methides by coordination to transition metals might have various applications, beyond the important structural and spectroscopic studies of these coordinated compounds. For example, it is possible to manipulate their structure while coordinated to the metal center and affect their controlled release and trapping, leading to new synthetic procedures. 

Transmetallation with RLi is used to prepare pure organolithium compounds for structural and spectroscopic studies. 

Most studies have been carried out on dehydrated zeolites of the HY or NaY type. Structural and spectroscopic studies have shown the occurrence of interaction between the CO ligands of [Mo(CO)6] and cations not belonging to the zeolite... 

Aime S, Diana E, Gobetto R, Milanesio M, Vails E, Viterbo D (2002) Structural and spectroscopic study of the dihydrogen bond in an imine triosmium complex. Organometallics 21 50-57... 

Structural and spectroscopic studies of pyrazino[2,3- ]pyrazine derivates were discussed in CHEC(1984) <1984CHEC(3)329>, and more recent data were reported in CHEC-II(1996) <1996CHEC-II(7)737>. Theoretical studies of the parent molecule, as for pyridazino[4,5- ]pyridazine, lead to the description of the nonbonding orbitals on nitrogen as perturbed naphthalene cr-orbitals, with contributions from cr -orbitals <1999PCA3089>. Infrared and Raman data for the parent have been reviewed and reassigned based on theoretical calculations <2000PCA7386>. 

Following their earlier work69 on iron(III) acetohydroxamate as a suitable iron source in iron-deficient anaemia, Brown et al.10 have carried out a detailed comparative structural and spectroscopic study of the complexes of Fem, Co11, Ni11 and Cu11 with aceto-, propiono-, benzo-, AT-methyl-... 

In Table 1 we have summarised the observed binding sites for Pt(II) to DNA fragments, usually proven by X-ray crystallography in the solid state, and by NMR spectroscopy in solution. It is not possible to review here the great variety of studies dealing with structural and spectroscopic studies on coordination compounds with nucleobases and derivatives. 

Ogata H, Lubitz W, Higuchi Y. [NiFe] Hydrogenases structural and spectroscopic studies of the reaction mechanism. Dalton Trans. 2009 (27) 7577-87. 

Maurus R, Bogumil R, Nguyen NT, Mauk AG, Brayer G. Structural and spectroscopic studies of azide complexes of horse heart myoglobin and the His-64-Thr variant. Biochem J 1998 332 67-74. 

Based on chemical, electrochemical, structural, and spectroscopic studies (2, 3), it has been concluded that the electron density in the metal orbitals does not change significantly as the charge level on the bis(dithiolene) complex is changed. Therefore, the accessibility of a range of charge levels of dithiolene complexes is perhaps more related to the accessibility of a number of formal oxidation states of the dithiolene ligands. Electrochemical and electron spin resonance (ESR) studies by Bowmaker et al. (41) support this view. One-electron... 

P. A. Davidse, J. L. M. Dillen, A. M. Heyns, T. A. Modro, and P. H. van Rooyen, Photochromic systems. Part 1. Structural and spectroscopic study of photochemically active products of Stobbe condensation. 2,3-dibenzylidene-succinic acid and its anhydride, Can. J. Chem., 68, 741-746 (1990). 

The structural and spectroscopic studies provide a firm foundation upon which to postulate a catalytic mechanism, but unfortunately give little insight into the activation of dioxygen within the reactive quaternary complex. Two key intermediates are presented in Figure 18. The first is an adduct of the coordinatively unsaturated iron(II) center, O2 and the nearby C4a of the BH4 cofactor, which is best described as an iron(II)-peroxypterin complex (Figure Since no intermediate has been directly... 

Figure 3.5 Structures of (a) [LaL3(HL)(phen)2(H20)] and (b) [EuL3(phen)(H20)] (HL = 4-aminobenzonic acid) [RE, black (large balls) O, grey N, black (small balls) C, white H, omitted]. (Redrawn from the GIF files of T. Fiedler et al, Synthesis, structural and spectroscopic studies on the lanthanoid p-aminobenzoates and derived optically functional polyurethane composites, European Journal of Inorganic Chemistry, 2007, 291-301, 2006 [40].)...

The variability of the inert pair systems is also evident in the class of the more halogen-rich oxo-trihaloselenates(IV), as shown from a number of recent structural and spectroscopic studies (251, 252, 262, 268, 297). They were prepared essentially according to the methods (a) and (c) indicated above. Depending on the counter-cation, the three different isomers of the SeOYa ion shown in Fig. 22 could be isolated and structurally characterized. In [CgHsNO JiSeOCla"] with 8-hydroxochinolinium as the cation (84), polymeric chains are observed with distorted square SeOC pyramids that have an apical Se=0 bond (1.59 A), two cis chlorines at 2.25 A and two bridging Cl at 2.96 and... 

As has been discussed briefly in Section III above, the ring strain of the cyclopropenes is accommodated, in part, by somewhat unusual bonding to the substituents. Structural and spectroscopic studies suggest that the vinylic C-H bonds have ca. 44% s character and that this is approximately constant in bonding to other substituents. Consequently aspects of the chemistry of the cyclopropenes are expected to reflect this with enhanced acidity of the vinylic proton. Cleavage of an exocyclic bond at C(3) will result in the cyclopropenyl cation, radical or anion with consequent interaction with the n bond and perturbation of the energy of the system. By comparison addition to the n-system to yield a cyclopropane relieves ring strain by ca. llOkJmol" ... 

Zhou YX, Yu B, Levon K (2003) The quest for Pd-II-Pd-II interactions Structural and spectroscopic studies and Ab initio calculations on dinuclear [Pdj(CN) (mu-diphosphane)j] complexes. Chem Mater 15 2774... 

The simplicity of the structure of phosgene has precipitated many structural and spectroscopic studies. This Chapter summarizes the results of the studies by electron diffraction, microwave and vibrational spectroscopy, nuclear magnetic resonance and nuclear quadrupole resonance spectroscopy, and mass spectrometry. Studies by electronic absorption and emission spectroscopy, and photoelectron spectroscopy, are discussed in Chapter 17. 

BLOOR Structural and Spectroscopic Studies of Poly diacetylenes... 

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