Staggered bonds

Conformations m which the torsion angles between adjacent bonds are other than 60° are said to have torsional strain Eclipsed bonds produce the most torsional strain staggered bonds none Because three pairs of eclipsed bonds are responsible for 12 kJ/mol (2 9 kcal/mol) of torsional strain m ethane it is reasonable to assign an energy cost of 4 kJ/mol (1 kcal/mol) to each pair In this chapter we 11 learn of additional sources of strain m molecules which together with torsional strain comprise steric strain... 

Molecules prefer conformations that stagger bonds on neighboring tetrahedral carbons (see Chapter 5, Problem 1). Does the same apply to trigonal carbons ... 

It is clear that this representation of c/5 -dimethyl-cyclohexane shows a plane of symmetry, and we can deduce it to be a meso compound. No such plane of symmetry is present in the representation of fran -dimethylcyclohexane. Why does this approach work Simply because the transformation of planar cyclohexane (with echpsed bonds) into a non-planar form (with staggered bonds) is a conformational change achieved by rotation about single bonds. The fact that cyclohexane is non-planar means we may have to invoke the conformational mobihty to get the three-dimensional picture. 

Fig. 4.35 The field ion images show two W adatoms forming a straight bond, or configuration 0, and staggered bonds, or configurations 1 on a W (112) surface. Also shown are pair energies at four bond distances for Re-Re pairs, from Ehrlich and co-workers, and W-W pairs, from Cowan and Tsong. interacting across the atomic channels of the W (112) plane.

Fig. 199. Rubber hydrochloride. Molecular configuration suggested by the repeat distance and the principle of staggered bonds. (Hydrogen atoms omitted.)...

The principal interest of the rubber hydrochloride structure (apart from its bearing on the theory of the relation between the physical properties and the molecular structure of polymers) is that it formed the first test of validity and usefulness of the principle of staggered bonds. Abnormal structures f In all the structures considered so far two... 

First, there is the chair form (Fig. 9.4). If we sight along each of the carbon-carbon bonds in turn, we see in every case perfectly staggered bonds ... 

Fig. 4.4. The normalized, staggered bond dimerization, of the ground state of an odd-site chain obtained by iterating eqn (4.21). The wavefunction of the mid-gap state, is also shown.

Fig. 4.12. The normalized, staggered bond dimerization, <5 , of the state for various extrinsic dimerizations, te. (The plotted results are scaled by the te = 0 values of So and. ) A = 0.2.

Fig. 10.8. The staggered bond dimerization in A as a function of bond index from the centre of the chain) of various states 1 A+ (diamonds), (circles) and...

Fig. 6.6 Dispersion of the electronic susceptibilities in Eq. (21) as a function of wavevector q for an alternating Hiickel chain with 8 = 0.20, hopping integral t = 1 and unit cell 2a = 1. The staggered bond order dominates at = 0. Source Ref. 60.

The TT-electron force constants in Eq. (24) can readily be found for butadiene, which motivated the reference force field F in Table 6.2. Since is phenomenological and PPP parameters include some core effects, the precise experimental identification of 7r-electron contributions emphasized above does not extend to precise theoretical connections to PPP or other models. PPP results indicating additional delocalization beyond butadiene can simply be associated with AF(N) = F N) - F 4). The staggered bond order couples to the out-of-phase combination, 5 = (5j - 52)2 of single and double bonds, and 5 is the special ECC coordinate [22] of PA. The PPP force constants for 5 -- are... 

---