Through-bond

The accuracy of an additivity scheme can be increased by going from atomic contributions through bond contributions to group contributions. 

The greater positive character hence the increased acidity of the O—H proton of 2 2 2 tnfluoroethanol can be seen m the electrostatic potential maps displayed m Figure 1 8 Structural effects such as this that are transmitted through bonds are called indue tive effects A substituent induces a polarization m the bonds between it and some remote site A similar inductive effect is evident when comparing acetic acid and its trifluoro derivative Trifluoroacetic acid is more than 4 units stronger than acetic acid... 

Cladding and backing metals are purchased in the appropriately heat-treated condition because corrosion resistance is retained through bonding. It is customary to supply the composites in the as-bonded condition because hardening usually does not affect the engineering properties. Occasionally, a post-bonding heat treatment is used to achieve properties required for specific combinations. 

The polarity of covalent bonds between carbon and substituents is the basis of important structure-reactivity relationships in organic chemistry. The effects of polar bonds are generally considered to be transmitted in two ways. Successive polarization through bonds is called the inductive fect. It is expected that such an effect would diminish as the number of intervening bonds increases. 

Let us now look at the details of this through-bond interaction mechanism. We consider the four-orbital system shown in Fig. 32. 

Pentadienyl radical, 240 Perturbation theory, 11, 46 Propane, 16, 165 n-Propyi anion conformation, 34 n-Propyl cation, 48, 163 rotational barrier, 34 Propylene, 16, 139 Protonated methane, 72 Pyrazine, 266 orbital ordering, 30 through-bond interactions, 27 Pyridine, 263 Pyrrole, 231... 

Through-bond interactions, 27, 47 Through-space interactions, 26 Trimethylene (edge-to-edge), 161... 

Originally the constant for the field/inductive effect was called the inductive constant ((jj). The field (through-space) contribution is, however, clearly larger than the inductive effect proper, i. e., the through-bond contribution. 

Fig. 3 A schematic illustration of through-bond and through-space interactions between the radical centers. The singlet-triplet energy gap, the activation energy (E, and the energy...

Fig. 5a-c Through-bond interactions in the triplet state of 1,3-diradical, a Mechanism of electron delocalization and polarization of a-spin electrons, b Cyclic orbital interaction, c Orbital phase continuity... 

As mentioned above, the unpaired electrons of diradicals may interact with each other through bonds. The orbital phase relationships between the involved orbitals control the effectiveness of the cyclic orbital interactions underlying the through-bond coupling. 

To summarize, the properties of triplet and singlet diradicals are closely related to the effectiveness of through-bond and through-space interactions, which are governed by the orbital phase continuity/discontinuity properties. In the next two sections, we will utilize this simple model to predict the spin preference and intramolecular reactivity for a broad range of diradicals. 

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