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I 2 Bonding

I, 2-bond (o/jQ - ov ap = 0.72 ct q - o/.nap = 0.585). This is because the order of the 2,3-bond is much lower than that of the 1,2-bond, so conjugative effects in particular are much less effectively relayed across the 2,3-bond. This again is exactly parallel to the effect of the chloro substituent in hydrogen exchange (protiodetritiation) of naphthalene (Scheme... [Pg.391]

Let us consider the first three structures (/, II and III in Table XXI) in which the tt bonds are only between neighbouring carbon atoms. These structures which may be referred to as the Kekul6 structures, will contribute more to the final state of the molecule than other forms because of the greater energy of the tt bonds. Since these three structures will contribute equally to the resultant molecule, the i—2 bond possesses two thirds double bond character, whereas the 2—3 bond possesses only one third double bond character. Thus the lack of equality of the bonds in naphthalene is explained. Furthermore, Sherman has shown that the symmetrical structure / makes a greater contribution to the resultant molecule than do the structures II and III. This will cause a further increase of the double bond character of the i—2 bond and a reduction of the double bond character of the 2—3 bond. [Pg.89]

Another uniformity concerns the special stability of aromatic hydrocarbons having 4n + 2 tt electrons n = 1 for benzene, n = 2 for naphthalene, etc. The reeison lies in the observation that, in such cases, all bonding m.o.s are filled whereas the anti-bonding ones are vacant. In these hydrocarbons, except for the lowest energy tt m.o. (two electrons), the bonding tt m.o.s invariably occur in pairs of degenerate orbitals - 4n electrons hence a total number of 4 -I- 2 bonding electrons. [Pg.227]

Cu(Tp CF3-)2)(C2H4)] has been prepared by the reaction of Na(Tp(CF3)2) with Cu(OTf) in the presence of ethylene. This compound has been characterized by 1H, 13 C, 19 F NMR, and IR spectroscopy and by X-ray crystallography and displayed notably high stability toward air oxidation and ethylene loss. X-ray structural data show a pseudotetrahedral copper ion and i 2-bonded ethylene units.204 [Cu(Tp1GF3l2)(NCMe)] has been also reported.221... [Pg.334]

For pairwise interactions we note that the Wk bond linking the white circles is equivalent to having a (I+/2) bond connecting each pair of white circles. [Pg.117]

This result follows from the fact that the projection of a given bond on the preceding bond is cos 0, while projections in two transverse directions averaged over free rotations are zero. This means that the projection of the k+i bond on the k+i—1 bond is cos 9, the projection of this projection on the k+i—2 bond is (cos 9), etc., which finally leads to the Eq. (5.12). The mean square end-to-end vector for freely rotating chain is... [Pg.69]

The total numbers of skeletal bonding orbitals in pyramidal nido systems generated by these three interactions are n — 1,1, and 2, respectively, leading to a total of 77 -I- 2 bonding orbitals holding 2n +4 skeletal electrons. Thus, the graph-theoretical treatment of nonpyramidal and pyramidal nido polyhedra with n vertices leads to the prediction of the same numbers of skeletal bonding orbitals, namely, n + 2, in accord with experimental observations. However,... [Pg.25]

I he results of their calculations were summarised in two rules. The first rule states that at least one isomer C with a properly closed p shell (i.e. bonding HOMO, antibonding I. U.MO) exists for all n = 60 - - 6k (k = 0,2,3,..., but not 1). Thus Qg, C72, Cyg, etc., are in lhi-< group. The second rule is for carbon cylinders and states that a closed-shell structure is lound for n = 2p(7 - - 3fc) (for all k). C70 is the parent of this family. The calculations Were extended to cover different types of structure and fullerenes doped with metals. [Pg.121]

Fig. 10. Demagnetization curves of hard magnetic materials A, Nd2Fe B B, Sm(Co, Cu,Fe,Zr)2 C, SmCo D, bonded SmCo E, Alnico 5 F, Mn—Al—C G, Alnico 8 H, Cr—Co—Fe I, ferrite , bonded ferrite. To convert T to G, multiply by 10". ... Fig. 10. Demagnetization curves of hard magnetic materials A, Nd2Fe B B, Sm(Co, Cu,Fe,Zr)2 C, SmCo D, bonded SmCo E, Alnico 5 F, Mn—Al—C G, Alnico 8 H, Cr—Co—Fe I, ferrite , bonded ferrite. To convert T to G, multiply by 10". ...
Four-membered heterocycles are easily formed via [2-I-2] cycloaddition reac tions [65] These cycloaddmon reactions normally represent multistep processes with dipolar or biradical intermediates The fact that heterocumulenes, like isocyanates, react with electron-deficient C=X systems is well-known [116] Via this route, (1 lactones are formed on addition of ketene derivatives to hexafluoroacetone [117, 118] The presence of a trifluoromethyl group adjacent to the C=N bond in quinoxalines, 1,4-benzoxazin-2-ones, l,2,4-triazm-5-ones, and l,2,4-tnazin-3,5-diones accelerates [2-I-2] photocycloaddition processes with ketenes and allenes [106] to yield the corresponding azetidine derivatives Starting from olefins, fluonnaied oxetanes are formed thermally and photochemically [119, 120] The reaction of 5//-l,2-azaphospholes with fluonnated ketones leads to [2-i-2j cycloadducts [121] (equation 27)... [Pg.853]

Step through the sequence of structures depicting rotation about the C i - C+ bond in 2-methyl-2-butyl cation. Plot energy (vertical axis) vs. CCCC dihedral angle (horizontal axis). What is the preferred conformation, with the ethyl group in plane or perpendicular to the plane ... [Pg.109]

For the preparation of compounds with an aromatic isoxazole system, two synthetic paths are of high importance first the condensation to form the 1—5 and the 2—3 bonds of the isoxazole ring (I—>2) and second that to form the 1—5 and 3—4 bonds of this... [Pg.366]

Construct a qualitative potential-energy diagram for rotation about the C-C bond of i,2-dibromoethane. Which conformation would you expect to be more stable Label the anti and gauche conformations of 1,2-dibromoethane. [Pg.105]


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See also in sourсe #XX -- [ Pg.679 ]




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