Beta bond

The most important cracking reaction, however, is the carbon-carbon beta bond scission. A bond at a position beta to the positively-charged carbon breaks heterolytically, yielding an olefin and another carbocation. This can be represented by the following example ... 

Garland SL, Dean PM. (1999) Design criteria for molecular mimics of fragments of the beta-turn. 2. C alpha-C beta bond vector analysis. /. Comput.-Aided Mol. Des. 13 485-498. 

Fig. 14.7 General reaction steps leading up to PAH formation. The reactions include abstractions (Abs.), beta-bond scission reactions (p), and addition reactions (Add.).

The use of alpha and beta bonds simplifies describing several familiar "inorganic" anions. Figure 7 illustrates the traditional Lewis structure of the sulfate ion, with an explanatory note that a more realistically picture (which will involve metric, as well as graph theoretical, distances [12]) is a tetrahedral resonance hybrid [13]. In other words, there are four identical oxygen atoms, each bonded by 1 and 1/2 bonds to the central sulfur atom, rather than two single and two double bonds. The name for this aggregation ... 

Because of the incorporation of beta bonds directly into the nomenclature, for conjugated monocyclic compounds having molecular formula C2nH2n there is no need to add a declaration of odd vs. even in order to distinguish between compounds which are aromatic vs. anti-aromatic namely, when n is odd the compound is aromatic vs. when n is even it is anti-aromatic. This is spelled out directly in the nomenclature The bonds between carbon atoms of a monocyclic aromatic compound have bond order of 1.5 thus the compound is nomenclated by the formula... 

Note that because of the use of beta bonds, rather than fixed single and double bonds, there is not inconsistency between the molecule depicted and the common vs. the alternate IUPAC names. The double bonds are NOT localized, as the IUPAC picture implies. To the contrary, 5H-Pyrrole is, because of symmetry just another (non-canonical) name for 2H-Pyrrole. Additionally, one should note that a 3H-Pyrrole can also be formed. This would have as its systemic name NP(CP)4 (1H). 

One of the main reasons why nodal nomenclature [42] was created was that the IUPAC organic nomenclature did not allow for assigning unique canonical names to members of the class of molecules referred to as "cyclophanes" a problem that would not have arisen had beta bonds been available. This is not to devalue the many virtues of nodal nomenclature, rather merely to show how the proposed system nomenclates these compounds without difficulty. 

As well as new properties of these molecules that have come to light with the discovery and nomenclating of the higher lullerenes and fulleranes, an extension that is unfathomable using traditional nomenclature, but is readily explained using beta bonds is next described when some of the carbon atoms are replaced by metal atoms in various of the smaller fullerenes. These molecules, which historically are not in the domain of... 

Bond incidence matrix for benzene using beta bonds... 

Fig. 9 The beta-bonded structure with added hydrogen atoms for "twisted zetherene" system as ...

To this stage our cluster wave function has been left in the general form of Eq. (1), with the restriction that double substitutions are confined to an active space. Within the active space, the double substitution operator couples together all pairs of occupied orbitals with all pairs of virtual orbitals. Physically we expect this description to be more complicated than is essential for a qualitatively correct description of the main correlations in bond-breaking. As is evident in minimal basis dissociation of H2, they are surely the alpha-beta bond-antibond correlations necessary to permit homolytic bond separation. 

So, restricting ourselves to the 1 1 perfect pairing active space, the simplest possible version of a CCD wave function would be to retain only the linear number of excitations needed to provide alpha-beta bond-antibond correlations ... 

Person, M.D., P.W. Kash, and L.J. Butler (1992b), Nonadiabatidty and the competition between alpha and beta bond fission upon [n,it (C=0)] excitation in acetyl and bromoacetyl chloride, J. Chem. Phys., 97, 355-373. 

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