Unexpected configurations

Latent failures—conditions present in the system for some time before the incident, but evident only when triggered by unusual states or events. Examples include equipment design deficiencies, unexpected configurations of munitions, or routine ignoring of standard operating procedures. 

The only other unexpected configuration among the first-row transition metals is that of copper, which is [Ar]45 3t/ ° rather than the expected [Ar]45 3(/ . 

Unsubstituted isopenams have been prepared as shown in Scheme 67 (80CC928). It is interesting but not unexpected that the thermodynamically preferred configuration has the 3-carboxylate and the H(5) cis. 

In the 6-chloro-A " series diazomethane addition and pyrazoline cleavage require more strenuous conditions. " An unexpected result is observed with the 4-chloro-A system (15) which adds two equivalents of diazomethane to give the 4-chloro-la,2a 6, 7 -dimethylene compound (16) in 16% yield after cleavage of the labile crude bispyrazoline with a catalytic amount of perchloric acid. The assignment of the -configuration to the 6,7-methylene group is based on the shift of the 19-H NMR resonance to higher field. 

The isolation of the -isomer 139 was in fact unexpected, since all tetrasubstituted olefins previously obtained from thiirene dioxide have been assigned the cis-configuration with respect to the two phenyl substituents based on the principle of least motion during the ring opening to olefins ". It might well be, therefore, that the -isomer is obtained through the isomerization of the initially formed Z-isomer. 

It is not unexpected that M(II) ions with configuration give hardly observable MMCT transition in combination with M(d°) ions. Since the ionization potential of the donor ion increases with its charge, the consequence of this observation must be that M(III) CT will always be at higher... 

To understand the interdependence of the creation of the two chiral centers relative to each other and to the sulfoxide, monosubstituted vinyl sulfoxides (S)-53 and (S)-54 were prepared and reduced with BH3-THF under the same conditions (Scheme 5.19). Both the 2- and 3-phenyl substituted substrates gave the chiral products 54 and 55 with complete stereo specificities dictated by the configuration of the starting sulfoxides. These results again were unexpected and indicated that both hydrogens were delivered solely directed by the chiral sulfoxide. This was not consistent with the mechanism in which the chirality of the initially formed chiral center at the 3-postion dictates the chirality of the subsequently formed chiral center at the 2-position. 

Thus, as expected from earlier work 36,37), the dioxabicyclization proceeds with inversion of configuration at the 3-position of the m-2-frans-3-dibromide 30, the stereochemistry at the 2-position being unaffected. However, experiments with individual diastereoisomers unexpectedly showed that the franj-2-m-3-dibromide 31, also reacts with silver trifluoroacetate, albeit less efficiently, to give the same bicyclic peroxide. We feel that this probably proceeds via an isomerisation (Eq. 25). 

The occupancies of metal 4d and 5s orbitals correspond to an overall s015d515 configuration, deviating noticeably from the nominal s°d5 assignment. The d spin-orbitals of a spin are essentially completely filled (0.993-0.995), and thus chemically inert. However, the nominally empty spin-orbitals of (3 spin exhibit significant non-zero occupancies (0.063 in each member of the eg set and 0.017 in each member of the t2g set), and appreciable occupancy of both spins is also found in the 5s orbital (0.088 a, 0.082 (3). These unexpected occupancies (which would be strictly absent in the isolated ion) can be associated with the leading donor-acceptor interactions, namely... 

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