Stable compound

Despite the occurrence of binary AIB2 borides (see also Fig. 2), no ternary representatives are known (Mn, Mo)B2 found from isothermal sections is a stabilized high-T phase by conversion to lower T by a statistical ( ) metal-metal substitution. Both MnB2 and M0B2 are high-T compounds stable above 1075°C and 1517°C respectively WB2 is claimed but is either metastable or impurity stabilized. Similar examples are observed with (W, Pd>2B5 (M02B5 type) as well as (Mo, Rh),, (B3 and (W, Ni), B3 (Mo,., 83 type). The phase relations in the B-rich section of the Mo(W)-B binaries, however, are not known precisely. 

Whereas adducts of instable stannylenes with bases are stable, easily isolatable compounds, stable stannylenes form adducts which are difficult to handle and to characterize. Taking [(Me3Si)2CH]2Sn (14) and Me2Si(NCMe3)2Sn (1) as examples 133 134), it is found that these two compounds can be coordinated with a base like pyridine (and also with other bases, see Ref.133)). However, the 1 1 adduct is only stable at —30 °C and decomposes at room temperature. The base attached to the stannylene can easily be removed in a vacuum at reduced pressure. When allowed to recondensate, it again forms a complex with stannylene 134). The equilibrium formulated by Eq. (10) can thus be shifted to the desired side. 

The amino-substituted five-membered heterocycles are unstable compounds, but their acetyl and formyl derivatives can be isolated. N-(Selenienyl-3)formamide can be obtained via the reaction route shown in Scheme ll.134 An ortho, electron-attracting substituent, such as formyl or nitro, renders amino compounds stable. However, the yield of 2-nitro-3-aminoselenophene is quite low. 

Simple dialkylgermanethiones are stable only at very low temperatures. A stable diaryl-germanethione (31) was synthesized with stongly sterically hindered aryl groups 11, as shown in reaction 14. The diarylgermanethione 31 is a solid crystalline compound, stable at room temperature. However, it undergoes addition reactions across the Ge=S double... 

N-Hydroxy-N-nitrosamines with an aliphatic group at O2 produce a compound stable to aqueous acid and base (Fig. 3.4, 29) [158], whereas all other N-hydroxy-N-nitrosamines are susceptible to hydrolysis and appropriate 02-derivatives also render these materials vulnerable. The hydrolysis endpoint is the formation of nitroxyl (HNO) [which dimerizes to form nitrous oxide (N20)] and a C-nitroso compound. These products are formed from aryl [159] and alkyl bound unsubstituted diazenium-diolates as well as Oralkylated derivatives [160]. Studies of the solvolysis of Oi-alkyl derivatives are complicated by their tendency to decompose via competing radical pathways [161], but the Oi-benzyl derivatives are unique in that they hydrolyze back to the original synthetic precursors (Scheme 3.14) [162]. 

XeF2 is a colorless crystalline compound stable up to 500°C, m.p. -129°C, with considerable vapor pressure for solids—4.5 mmHg (20°C). It is a linear symmetrical molecule. The mean thermochemical energy of the Xe—F bond in XeF2 is 132kJ/mol,3 which is less than the F—F bond energy—157.3 kJ/mol.4... 

All elements that form solid, liquid, and gaseous compounds stable over a wide temperature range are likely to have variations in isotopic composition. Generally, the heavy isotope is concentrated in the solid phase in which it is more tightly bound. Heavier isotopes tend to concentrate in molecules in which they are present in the highest oxidation state. 

Replacement of hydrogen by alkyl groups gives compounds like lithium triethylborohydride (Super-Hydride ) [100], lithium tris sec-butyl)borohydride [101] (L-Selectride ) and potassium tris sec-butyl)borohydride (K-Selectride ) [702], Replacement by a cyano group yields sodium cyanoborohydride [103], a compound stable even at low pH (down to 3), and tetrabutylammonium cyanoborohydride [93],... 

Unstable compound stable only in dilute aqueous solutions solution turns yellow on standing decomposes when heated to 100°C. 

The compounds included in this section are very ephemeral due to the instability of the 000 and OOOO chains at room temperature. In Section VtlLA the primary ozonides were mentioned, and they may be conserved for some time at low temperatures. An example of a compound stable at room temperature (296) is mentioned in Section Vin.C.4. A brief review appeared of unstable ozonization products derived from various sources, involving hydrotrioxides . ... 

In several cases thietane derivatives have been used as ligands in organo-metallic compounds. Stable enolate complexes have been derived from tetra-methyl-3-thietanone and diiron nonacarbonyl. Both compounds were heated in n-hexane at 60°C in an argon atmosphere for longer periods of... 

Now that we have an understanding of radioactive isotopes and their utility in constraining the timing and rates of nebular, planetesimal, and planetary processes, we will turn our attention to the most volatile elements and compounds. Stable isotopes in them provide additional constraints on cosmochemical processes. 

So far, the discussion of the influence of temperature on the stability of chemical compounds has shown, in a qualitative way only, that, on increasing temperature, compounds stable at low temperature will first decompose into compounds with smaller molecules, secondly into atoms and finally into ions and electrons. 

Boron has two isotopes, 10B (20%) and nB (80%), of which the former strongly absorbs neutrons to give a-particles according to equation (21). One aim of the work with boron heterocycles was to find nontoxic compounds, stable in the human body, for use in neutron capture therapy of cancer. It was hoped that boron-nitrogen analogues of benzene or pyridine should have derivatives with these properties, but no such compound has been found. 

Amino-substituted selenophenes are in general unstable compounds, and are conveniently isolated as IV-acetyl or iV-formyl derivatives. An ortho situated electron-attracting substituent such as acetyl, formyl or nitro renders the amino compounds stable. Derivatives of this type can be diazolized and the resulting diazonium salts converted into azides (by reaction with azide ion) (75CR(C)(281)317) and selenocyanates (by reaction with selenocyanide ion) (79BSF(2)237). 3-Acetamidoselenophene can be thiocyanated or selenocyanated in the 2-position by treatment with bromine and potassium thiocyanate or potassium selenocyanate, respectively (78TL1797). 

It was felt initially that unstable cycles have only an academic interest in the sense that they cannot be final states. However, I realized later that compound stable cycles can be derived from each simple stable cycle, by incorporation of 1, 2, 3,. . . m,. . . runs of the unstable cycle. For instance, from the simple stable cycle C , one can derive an unlimited number of compound cycles (Cl, C2,. . . C ,. . . ) ... 

A series of studies were conducted to define parameters related to reactivity, solubility, and stability of alkoxysilane hydrolysis mixtures for the purpose of generating model compounds stable in water solution and maintaining coupling agent activity. 

The first neutral silaaromatic compound stable at room temperature was recently synthesized by Okazaki and coworkers6,272. The 2-silanaphthalene 573 is characterized by... 

A major advance in silylene chemistry over the past five years has been the synthesis of persistent dicoordinate silicon compounds stable silylenes . 

The structure of beryllium(II) chloride in its various phases has been described, together with the relevant thermochemistry, in Section 3.3. The dimer Be2Cl4 is an example of scheme (2) bonding, while the chain structure of BeCl2(s) represents scheme (3). Scheme (2) is rather unusual, and in compounds stable at room temperature it is mainly restricted to some organometallic compounds of Be. The example given in Table 6.3 has the structure ... 

The methyl esters can be also determined by GC-FID. Using a 30 m x 0.32 mm ID x 0.25 pm (film thickness) capillary column, such as DB-1701 or equivalent, the compounds can be adequately separated and detected by FID. The recommended carrier gas (helium) flow rate is 35 cm/s, while that of the makeup gas (nitrogen) is 30 cm/min. All of the listed herbicides may be analyzed within 25 min. The oven temperature is programmed between 50 and 260°C, while the detector and injector temperatures should be 300 and 250°C, respectively. The herbicides may alternatively converted into their trimethylsilyl esters and analyzed by GC-FID under the same conditions. FID, however, gives a lower response as compared with ECD. The detection level ranges from 50 to 100 ng. For quantitation, either the external standard or the internal standard method may be applied. Any chlorinated compound stable under the above analytical conditions, which produces a sharp peak in the same RT range without coeluting with any analyte, may be used as an internal standard for GC-ECD analysis. U.S. EPA Method 8151 refers the use of 4,4,-dibromooctafluorobiphenyl and 1,4-dichlorobenzene as internal standards. The quantitation results are expressed as acid equivalent of esters. If pure chlorophenoxy acid neat compounds are esterified and used for calibration, the results would determine the actual concentrations of herbicides in the sample. Alternatively, if required, the herbicide acids can be stoichiometrically calculated as follows from the concentration of their methyl esters determined in the analysis ... 

---