Nomenclature dissociation energy

There are numerous publications where the standard enthalpy of reaction 5.1 is calledbond dissociation energy and abbreviated by BDE or by >(A-B). However, this designation (as well as the abbreviations) can be misleading, and we favor the nomenclature just indicated. It should also be recalled (see section 2.2) that the International Union of Pure and Applied Chemistry (IUPAC) recommends Do for the dissociation energy at T = 0 (therefore, Do = DUfi = DH ) and De for the hypothetical dissociation energy from the potential minimum [13],... 

However, if we take the CH4 molecule apart stepwise, we get four different results that we may call the bond dissociation energies D (the nomenclature is arbitrary) ... 

The acronym SEC refers to the case where the reference wave function is of the MCSCF type and tire correlation energy is calculated by an MR-CISD procedure. When the reference is a single determinant (HE) the SAC nomenclature is used. In the latter case the correlation energy may be calculated for example by MP2, MP4 or CCSD, producing acronyms like MP2-SAC, MP4-SAC and CCSD-SAC. In the SEC/SAC procedure the scale factor F is assumed constant over the whole surface. If more than one dissociation channel is important, a suitable average F may be used. 

One can draw a useful analogy between acid-base and oxidation-reduction reactions. Both involve the transfer of a species from a source, the donor, to a sink, the acceptor. The source and sink nomenclature implies that the tendency of the proton (in the case of acids) or of the electron (for reducing agents) to undergo transfer is proportional to the fall in free energy. From the relation AG° = RTIn Ka. you can see that the acid dissociation constant is a measure of the fall in free energy of the proton when it is transferred from a donor HA to the solvent H2O, which represents the reference (zero) free energy level of the proton in aqueous solution. 

Figure 3.5 Nomenclature for peptide sequencing. Fragments resulting from backbone cleavages are mainly observed when MALDI peptide ions are fragmented in low-energy collision-induced dissociation (CID) tandem mass spectrometers. Of these, the cleavage at the amide bond will be most efficiently cleaved, resulting in y- and b-ions, depending on which part of the peptide will...

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