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Bond stretch isomers

Molecular equilibrium structures of the same spin state which - still hypothetically - differ only in the length of one or several bonds. [Pg.140]

The energy required to break a given type of bond between atoms ( i.e., to separate the atoms infinitely). [Pg.140]

Separation of the wavefunction into electronic and nuclear parts  [Pg.140]


This isomerization is a symmetry-forbidden one, since a level crossing such as the ones found in trimethylene and tetramethylene is found (22) (Fig. 13). It should be noted that, in all these cases, the two-minima structure due to level crossing might, in principle, be swept out by configuration interaction. If the barrier survives, however, the two isomers [4] and [5] can be called bond-stretch isomers. Another example is the isomerization [6] [7] (23). [Pg.17]

FIGURE 5. Possible conversion of the bond-stretch isomer to a tetrasilatetrahedrane upon replacement of the substituents in circles by more bulky silyl groups. Reproduced with permission from Reference 10. Copyright 1995 American Chemical Society... [Pg.127]

FIGURE 14. Bond-stretch isomers of [1.1.0]metallabicyclobutanes 2. Polycyclic and polyhedral metallanes... [Pg.52]

However, experimental studies soon showed that in the original case and apparently in all similar ones, as well as more complicated ones,14 no such bond stretch isomers exist. The isomer(s) with the longer bond are simply the normal (short- bonded) molecule co-crystallized with an impurity so that at some crystal sites a M—Cl bond occurs where there would be an M=0 bond in the pure oxo compound. The refinement of X-ray data from such a mixed crystal leads to the appearance of a longer M=0 bond. Also, the contamination of a blue compound by a yellow impurity gives the appearance that there is a green compound. From the theoretical side the concept seems counter-intuitive (reminiscent of polywater ) and, indeed, a high-quality molecular quantum study15 failed to confirm the earlier theoretical support. [Pg.38]

Parker, G. Do bond-stretch isomers really exist Acc. Chem. Res. 25, 455-460 (1992). [Pg.453]

NbECl3 (E= O, S) and their simple adducts remain very useful synthons (see, e.g., ref. 237-241). The systems NbECl3(PR3)2j3 (E = 0, s)240,241 have been at the forefront of the controversy concerning distortional (bond stretch) isomers.242-246... [Pg.261]

The copper(I) complexes of the tetradentate ligands and occur in three struc-turai forms two have been characterized by singie-crystai X-ray diffraction and are distortionai isomers (bond-stretch isomers [35-37], see Figure 18-11) [3, 38, 39]. [Pg.400]

The results of ab initio M.O. calculations, using a very restricted basis set, indicate that it may be possible to obtain in practice bond stretch isomers in the system (30). When the N and B are replaced by carbon atoms, the species at the right-hand side can never be isolated. [Pg.83]

Fig. 3 Original, incorrect proposals for the structures of blue and green isomers of MoOCl2(PMe2Ph)3. (a) cis and trans isomers (b) distortional (bond-stretch) isomers with short and long Mo=0 bonds. Fig. 3 Original, incorrect proposals for the structures of blue and green isomers of MoOCl2(PMe2Ph)3. (a) cis and trans isomers (b) distortional (bond-stretch) isomers with short and long Mo=0 bonds.
Fig. 4 Other examples of originally proposed bond-stretch isomers. Fig. 4 Other examples of originally proposed bond-stretch isomers.
Parkin. G. Hoffmann, R. Bond-stretch isomers and spin-state isomers A comment on the article Bond-Stretch Isomers Fact not Fiction. Angew. Chem., Int. Ed. Engl. 1994. 33, 1462. [Pg.126]

Finally, if 2 symmetry is broken, which happens if one of the F atoms in SF2(b A2) is replaced with Cl to yield SFC1( A"), two distinct minima are possible, one where the recoupled pair bond is between S and F and one where it is between S and Cl. We showed that SFC1( A") does indeed have two bond stretch isomers, although the barrier between the isomers is very small [13]. [Pg.62]

The recent synthesis of tetrasilabutadiene 1 [1] and of tetrasilacyclobutene 2 [2, 3] in the groups of Weidenbruch and Kira, respectively, has renewed the interest in Si4H6 isomers, their properties and their interconversions. The bicyclic compound 3 [4] has attracted considerable interest in the past, both theoretically and experimentally, due to the possibility of bond-stretching isomers [5,6]. More recently the groups of Kira [7] and Sekiguchi [8] were also succesful in the synthesis of silyl-substituted trisilacyclopropenes 4. [Pg.110]

As pointed out in Section II.B, tetrasilatetrahedrane (Si4R4) collapses with no significant barrier to a two-bond broken isomer when R = H, the latta being 37.3 kcal mol more stable at the BLYP/6-31G level . This enagy diffaence is decreased by 8.9 kcalmol with R = Me, but the two bonds still ranain broken. However, when R = SiHs, the bond-stretch isomer is by only 10.4 kcalmol more stable than the corresponding tetrasilatetrahedrane, having only one bond stretched. As Figure 5 shows, the structural features of the two isomers, especially the close contact between the substituents... [Pg.125]


See other pages where Bond stretch isomers is mentioned: [Pg.258]    [Pg.131]    [Pg.123]    [Pg.125]    [Pg.126]    [Pg.128]    [Pg.1467]    [Pg.500]    [Pg.500]    [Pg.41]    [Pg.52]    [Pg.54]    [Pg.2752]    [Pg.471]    [Pg.466]    [Pg.466]    [Pg.90]    [Pg.2751]    [Pg.11]    [Pg.120]    [Pg.120]    [Pg.121]    [Pg.127]    [Pg.202]    [Pg.203]    [Pg.108]    [Pg.338]    [Pg.123]    [Pg.126]    [Pg.128]    [Pg.1467]   
See also in sourсe #XX -- [ Pg.131 ]




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