O-Aromaticity

Reaction o( aromatic amines with sulfur nxMiochioride and an acyi chlonde in the presence o( Zn salts to give 1,3-benzothia20ies... 

B+ (Psh, A, ) la1 2le1 4le2 4la2"22a1 2 5 1 1 Ti-Aromatic o-Aromatic... 

Scheme 3.2-44. From two-dimensional n aromatics (planar 2, C2BH3) to three-dimensional o aromatics (polyhedral 15, 39 and higher members of the series) via folded aromatics (3, 2 ) connecting both classes.

Fig. 14 Chemical shift anisotropy (< 33— 11) for the protonated (O) aromatic carbons and unprotonated ( ) aromatic carbons in PET (from [12])...

Fig. 17 Cross-polarisation contact times, fi/2, for the aromatic carbons in the phenyl rings, in both the pure PET and the PET/TPDE blend O aromatic carbons in PET and aromatic carbons in the blend that contains 10% TPDE (from [12])...

Aromaticity is not only related to the 7i-system. Cyclopropane, the saturated three-membered ring is considered to be o-aromatic [92, 93], The o-aromaticity, which results in stabilization [93] but also in magnetic properties [87], is not restricted to carbon. The saturated three-membered rings containing nV. -P atoms (1-3) (see Scheme 7) were also shown to be aromatic [94], It is, however, difficult to separate the stabilizing effect of this type of aromaticity from ring strain. 

The diphosphirenium cation with two a A,5-P atoms (14) has also been reported. For an explanation of its stability, the effect of o aromaticity (interaction of the lone pair at the carbanion with the a PN antibonding orbitals) has been considered, although it has not been further investigated [120],... 

Figure 3.16. The Stern-Volmer constant as a function of the half-wave potential E /2 for the reactions with trivalent phosphorus compounds (o), aromatic amines ( ), aliphatic amines ( ), and alkoxybenzenes (A)- The solid broken line represents the diffusional (horizontal) and kinetic branches of Ko for the irreversible reaction, while the dotted line is k from Eq. (3.22). The dashed curve represents Ko for reversible reactions. (From Ref. 121.)...

O aromatic / lipophilic O H-bond donor I H-bond acceptor H-bond donor 4 acceptor... 

The term in-plane aromaticity has been used for molecules such as the didehy-drophenyl cation (see Section II). However, we stress that the compounds in question are homoaromatic rather than aromatic molecules, which can be directly related to a-aromaticity Therefore, the appropriate notation should be homo-o--aromaticity rather than in-plane aromaticity. The concept of c-aromaticity is very controversial. One can completely avoid this term by referring to the mode of electron delocalization as was done by Cremer While 7r-aromaticity and homo-7r-aromaticity are connected with ribbon delocalization of electrons along a conjugative cycle, molecules that have been considered to be either a-aromatic or homo-o--aromatic (in-plane aromatic) seem to prefer delocalization of electrons over a surface defined by the participating atoms (see the discussion in... 

Trimesitylgermyllithium was isolated as a yeUow solid in the form of a THE complex in 62% yield (equation 5). The polarity of the germanium-hthium bond was evident from the high field shift of the Mes signals in NMR spectra and the low field shift of the /p o-aromatic carbons in NMR spectra. 

Carbon is unique in its ability to form long chains of like atoms. Its compounds within each series react similarly, but not identically, chemskiii Builder 24.1 O Aromatic hydrocarbons do not react very similarly to alkenes or alkynes. 

Dewar suggested one further type of stabilization for cyclopropane. In analogy with benzene, which is stabilized by aromaticity provided by six ji-electrons, Dewar argued for o-aromaticity provided by the six o-electrons of the C-C bonds of cyclopropane. Dewar s arguments lay with simple MO theory and energetic analysis. 

It should be noted, however, that the concept of o-aromaticity is fairly limited in its applicability—to just three-member rings—certainly in contrast to the notion of aromaticity. For example, aromaticity can be nsed to gronp componnds with differing ring sizes (benzene, naphthalene, cyclopentadienyl anion, tropylinm cation, etc.), but no one is suggesting that cyclopentane, which has 10 o-electrons, exhibits... 

Cremer, D. Gauss, J. Theoretical determination of molecular structure and conformation. 20. Reevaluation of the strain energies of cyclopropane and cyclobutane - CC and CH bond energies, 1,3 interactions, and o-aromaticity, J. Am. Chem. Soc. 1986, 108, 7467-7477. 

The effect of reduced FBP on catalyst deactivation is not related to the reaction temperature as this was similiar for the naphthas with different FBP (Figure 9). Therefore the amount of coke precursors in the heavy end is the important factor. Table II presents the identified C,o aromatics (the heaviest components present in more than just trace concentrations) in the reformate at 102.4 RON. There is a distinct difference between the base naphtha and the FBP 149 °C naphtha with respect to feedstock as well as reformate content of propyl-toluenes and n-butylbenzene, which both can form bicyclic aromatics through direct side-chain cyclization. 

A Aliphatic ethers Halogenated ethers o Aromatic ethers... 

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