Structural trends

TABLE 3. HF/3-21G energy, zero-point energy (ZPE), HF/3-21G( ) and MP4/6-31G total energies and relative energy (RE) for silicon compounds  

Reprinted with permission from J. Am. Chem. Soc., 108, 260 (1986). Copyright (1986) American Chemical Society68. 

TABLE 4. HF/3-21G( optimized Si-H and Si-X bond lengths and H-Si-X bond angles for H3SiXH molecules  

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Lesk, A.M. Themes and contrasts in protein structures. Trends Biochem. Sci. 9 June V, 1984. 

Edison, A.S. Propagation of an error p-sheet structures. Trends Biochem. Sci. 15 216-217, 1990. 

Interesting stabilization and structural trends have been noted using MP2/6-31G calculations on the effect of substituents on imines. The data below give AE for the isodesmic reaction and show that stabilization tends to increase with Xbe 1 gi (>up electronegativity of the substituent. The X—N=CH2 bond angle decreases with Xbe-... 

The correlation of structural and vibrational parameters, and a detailed analysis of structural trends based on the available wealth of electron diffraction, microwave and X-ray structural studies on sulphoxides and sulphones, have been reported by Hargittai in a comprehensive study20 which will stand for a long time as a milestone in the structural... 

A major goal was to investigate the solid state structures of such compounds by single crystal X-ray diffraction. It was found that Lewis acid-base adducts R3M—ER3 show general structural trends, which allow estimations on the relative stability of the adducts. The experimental results were confirmed by computational calculations, giving even deeper insights into the structural parameters and the thermodynamic stability of simple Lewis acid-base adducts. In addition, their thermodynamic stability in solution was investigated by temperature-dependent NMR spectroscopy. 

Reliable information on the thermodynamic stability of group 13/15 adducts is usually obtained by gas phase measurements. However, due to the lability of stibine and bismuthine adducts in the gas phase toward dissociation, temperature-dependent H-NMR studies are also useful for the determination of their dissociation enthalpies in solution [41b], We focussed on analogously substituted adducts t-BusAl—E(f-Pr)3 (E = P 9, As 10, Sb 11, Bi 12) since they have been fully characterized by single crystal X-ray diffraction, allowing comparisons of their thermodynamic stability in solution with structural trends as found in their solid state structures. 

In the structure 24a, the triphenylphosphine is strongly bound to the electrophilic phosphorus centre (PP=2.206A) which indicates a strong covalent character of this bond. Upon warming the solution to 20 °C decomposition takes place and a mixture of bicyclotetraphosphanes is formed. Interestingly, some structural trends towards the formation of ion pairs between a donor and an acceptor were also reported in the push-puU diphosphene structures 25-27 [69] (Fig. 4). 

Ozawa, 1963 Sugimura and Uyeda, 1973). For example, Sugimura and Uyeda (1973) summarized volcanic rocks, degree of deformation of sediments, structural trends of sediments deposited, and amount of uplift and subsidence since Miocene. 

Wang JX, Robinson IK, DeVilbiss JE, Adzic RR. 2000. Structural trends among ionic mental-haUde adlayers on electrode surfaces. J Pbys Cbem B 104 7951-7959. 

U. Hausermann, High-pressure structural trends of group 15 elements. Chem. Eur. J. 9 (2003) 1471. 

Advances in Structural Trends and Spectroscopy of Nickel Complexes 275... 

Schafer, L., J. D. Ewbank, V. J. Klimkowski, K. Siam, and C. Van Alsenoy. 1986. predictions of Relative Structural Trends from Ab Initio Derived Standard Geometry Functions. J. Mol. Struct. (Theochem) 135, 141-158. 

Danesi, P. R. Reichley-Yinger, L. Mason, G. Kaplan, L. Horwitz, E. P. Diamond, H. Selectivity structure trends in the extraction of cobalt(II) and nickel(II) by dialkyl phosphoric, alkyl alkylphosphonic, and dialkylphosphinic acids. Solvent Extr. Ion Exch. 1985, 3, 435 152. 

Cross TA, Sharma M, Yi M, Zhou HX (2011) Influence of solubilizing environments on membrane protein structures. Trends Biochem Sci 36 117-125... 

Structural Trends within Alane and Gallane Adducts... 

These experimentally observed structural trends were confirmed by computational calculations on H3A1 and Me3Al adduct families. In each adduct family, the amount of increase of the M-X bond lengths and decrease of the X M-X bond angles (X = H, Me) compared to uncomplexed MX3 diminishes with the atomic number of the group 15 element. The structural trends very well reflect the trends observed for the thermodynamic stability of such adducts, as is illustrated in Tables XI and XII. 

Beck TJ, Looker AC, Ruff CB, Sievanen H, Wahner HW (2000) Structural trends in the aging femoral neck and proximal shaft analysis of the Third National Health and Nutrition Examination Survey dual-energy X-ray absorptiometry data. J Bone Miner Res 15 2297-2304... 

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