Bonds Aromatic

Bonds Single, double, triple, and aromatic (or conjugated) bonds are indicated by the symbols and " respectively single and aromatic bonds should be omitted. 

A con jugated sp - -sp --" single bond (for example, the bond joining the tw o phenyl rings of biphenyl, the central bond of butadiene, with delocali/ed aromatic bonds, or phenyl amine, where N-G bond is labeled aromatic and nitrogen is sp2 b h ybridi/ed) IS described by a two-fold barrier, V2=l() kcal/mol. 

Aromatic bonds (as in benzene) have a two-fold barrier of V2=25 kcal/mol. 

Os04 will add to C=C bonds but will only attack the most reactive aromatic bonds thus benzene is inert, but it will attack the 9,10 bond in phenanthrene and will convert anthracene to 1,2,3,4-tetrahydroxytetra-hydroanthracene. It can be used catalytically in the presence of oxidizing agents such as NaC103 or H2O2 [53],... 

Among the compounds that form complexes with silver and other metals are benzene (represented as in 9) and cyclooctatetraene. When the metal involved has a coordination number >1, more than one donor molecule participates. In many cases, this extra electron density comes from CO groups, which in these eomplexes are called carbonyl groups. Thus, benzene-chromium tricarbonyl (10) is a stable compound. Three arrows are shown, since all three aromatic bonding orbitals contribute some electron density to the metal. Metallocenes (p. 53) may be considered a special case of this type of complex, although the bonding in metallocenes is much stronger. 

Log P calculation for quinidine with the atom contribution method according to Ghose and Crippen. R group connected to C X heteroatom = double bond aromatic bond aromatic single bond (e.g. C=N in pyrrole) subscripts give the hybridization state and superscripts the formal oxidization number. For the quinidine structure see Fig. 14.1. 

Reaction of [cp IrCl2]2 with 2,6-dimethoxyphenyl(diphenylphosphine), mdmpp, gives (222), and with tris(2,6-dimethoxyphenyl)phosphine, tdmpp, gives (223).394 Addition of tcne to a CH2C12 solution of (222) yields the structurally characterized complex (224), in which tcne has inserted into a C—11 aromatic bond.395 The complex (223) reacts with one molar equivalent of tcne to give (225), and with two molar equivalents to give (226) both have been analyzed by X-ray crystallography.396... 

Table 1 Calculation of some molecular-based descriptors for BOA, DIMBOA and MBOA. Physicochemical descriptor like logP (partition coefficient between octanol and water) constitutional descriptors like the number of a specified atoms or bonds (number of carbons, hydrogens, oxygens, nitrogens, single and aromatic bonds, the total number of atoms and bonds) and molecular weight quantum-mechanical descriptors like HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital).

Fragments in compounds 155—157 exhibit aromatic bond delocalization. The lowest aromaticity is calculated for Af-pyridinium cyclopentadienide 157, with the interfragmental C—N bond shorter than the corresponding one in 155 and 158. The phenolate moiety in 159 has a high NICS value (—4.6 ppm), in agreement with the one for deprotonated phenol (—6.2 ppm compared to —9.7 ppm for benzene, as cited),196 while the acceptor pyridinium counterpart has a NICS value of —5.5 ppm, showing aromatic delocalization. 

In the ortho positions, the substituent chemical shifts are between those for a double and a single bond, as would be expected on the basis of an aromatic bond. For these positions proximate interactions such as electric field effects assume an increased importance. 

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