Secondary eclipse

Observational evidence for the dynamic mass-flow phase includes (A) light-curves where the secondary eclipse becomes deeper at shorter wavelengths (Kondo et al. 1985), (B) the non-monotonic variation of the spectral energy distribution which is pronounced in the ultraviolet (Kondo et al. 1985), and (C) continued presence, both inside and outside the eclipses, of emission features observed in beta Lyrae (Hack et al. 1977). Phenomena (A) and (B) have been attributed to the presence of variable, optically-thick, extrastellar plasma. 

Different strategies exist to characterize a planet s atmosphere direct detection resolves the planet and star individually, and transmission as well as secondary eclipse measurements subtract the stellar light fi om a combined star-planet detection. For directly imaged planets, in the visible part of the spectrum, we observe the starlight, reflected off the planet in the thermal IR we observe the planet s own emitted thermal flux. An Earth-like, temperate planet is a very faint, small object close to a very bright and large object, its parent star. 

Belu AR, Selsis F, Morales J-C, Ribas I, Cossou C, Rauer H (2011) Primary and secondary eclipse spectroscopy with JWST exploring the exoplanet parameter space. Astron Astrophys 525, id.A83... 

The eclipsed conformations of 29, 48, and 32 bring the pairs of Sb and Bi atoms on opposing rings very close (3.58-3.69 A). These distances are significantly shorter than van der Waals radius separation (4.4 A for Sb Sb and 4.6 A for Bi Bi). Thus a direct secondary bonding between the pnictogen atoms seems likely. 

Dimethyl-2-isopropylethylene (61) affords the secondary hydroperoxide 62 in ayield higher than 95%.7,104 The most stable conformation of 61 is 63 in which the hydrogen at C3 is eclipsed with the double bond, the most unfavorable position of an allylic hydrogen for the reaction... 

U Cephei (V = 6.8-9.0, P = 2.493 d) is an eclipsing binary consisting of a B7V primary and a G8DI-IV secondary component. This binary is one of the semidetached Algol systems showing soft X-ray emission which is probably associated with a hot corona surrounding the secondary component (White and Marshall 1983). 

The singlet states obtained by addition ofCH3+ orH+to TiCl2 and electron donation from Ti(II) to the cation are secondary minima, 5.1 kcal/mol and 39.7 kcal/mol above the triplet state, respectively. Structures are pyramidal the eclipsed form, which is not the best, shows the agostic effect [3, 4], In theground state (triplet), the methyl is bound to a chlorine atom (dc cl = 1.86 A) that is distant from the titanium atom (dTicl = 2.46 A). 

Once the most reactive substrate conformations are known, it remains to look for the best approach of the nucleophile. An anti attack is promoted by a favorable secondary overlap between the nucleophile and o (C L), which is shown by the double arrow. Syn attack is disfavored, both by a negative secondary overlap (wavy line) and by the eclipsed relationship between C L and Nu---C (Figure 6.6). To summarize, the Felkin transition states are favored because they correspond to the best trajectories for attacking the most reactive conformations. 

Grieco has used his aqueous imnicmium Diels-Alder procedure to effect a number of intramolecular reactions. In one case, diene aldehyde (83) was treated with ammonium chloride to afford a 2.2 1 mixture of isomeric Diels-Alder adducts (87) and (85) (Scheme 10). Since intermediate immonium ions (84)/(86) cannot participate in secondary orbital effects as is the case with A-acyl imines (c/. 80), these results are probably due to steric factors. It was suggested that adduct (85) derives from conformation (84) and adduct (87) comes from (86). Conformer (84) is favored since there is a severe eclipsing of Ha b in (86). A more detailed account of the stereochemical aspects of intramolecular Diels-Alder reactions can be found in Chapter 4.4. 

A conformational analysis of various substituted A-homo-steroids is reported. The preferred conformation of the amide group in some acetamido-substituted steroids is of the type (5), with anti-periplanar orientation of C—H and N—H bonds the eclipsing of the C—H and C=0 bonds is similar to that accepted for acetates of secondary alcohols. 

Houk has explained this in terms of secondary orbital interactions of the most eclipsed allylic sigma bonds with the tc LUMO [28, 511. 

Ramalingam and coworkers have performed detailed computational studies at various levels of theory with respect to the insertion of HCIC and CbC singlet carbenes into the carbon-hydrogen bond of small alkanes and identified two insertion modes (Fig. 6.8)." Of these, the a approach has been found to be preferred over the n mode at all levels of theory because the k attack leads to the eclipsed conformation (compare transition state 143 to 144, which is a secondary saddle point). In the initial phase of the insertion process there is a net charge flow from the alkane to the carbine. Barriers for the insertion... 

An ab initio SCF calculation of Cp2Ge calculated a linear structure (38) rattier the experimentally reported bent structure (5b,60). However, it was pointed out that the lone pair electrons on Ge were stabilized in a bent geometry and that the 2>d electrons of Ge were of secondary importance in bonding between Cp and Ge (39). Recent SCF calculations of Cp2Sn and Cp2Pb showed both metallocenes have C2v eclipsed stmctures as the lowest-energy conformer (40). However, the calculated C(Cp)-E distances are quite different from the experimental values (see Table 3) (5b,8,41). 

Fig. 6. The mass-radius relation for both components in each of fifty eclipsing binary stars. The primaries and secondaries are shown as squares and circles (based on [19])...

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