Neutral rings

Inorganic Rings and Polymers of the p-Block Elements From Fundamentals to Applications 

Interestingly, an attempt to produce the trimer (BNMe2)s by reductive coupling of monoboron and diboron fragments generated (in very low yield) a colourless compound 9.3 that had the molecular mass of the hexamer 

For the heavier group 13 elements, there is an extensive cluster chemistry of neutral oligomers of the type (MX) (X = halide), (MR) (R = alkyl) or (MNR2) . For example, the series of tetramers [MC(SiMe3)3]4 (M = A1, Ga, In, Tl) all form tetrahedral structures,cf. (B Bu)4. In the formal + 1 oxidation state, these elements do not form monocyclic ring systems even with the stabilising influence of dialkylamino substituents. 

---

Dihydro-lH-l,2-azaboroles derive from cyclopentadiene by the isoelectronic replacement of a C=C group by a BN moiety ". The neutral rings react in xs boiling Fe(CO)j without any other solvent to form red-brown iron-dihydro-1,2-azaborolyldi-carbonyl dimers as their cis and transisomers in 56% yield, or with CojfCOg in petroleum ether at 60-80°C to the half-sandwich complex (dihydro-1,2-azaborolyl)Co(CO)2 (40%). The CO group can easily be substituted by olefins ... 

Exercise 3.2. Verify that the net charge at each carbon atom of each of the neutral ring systems shown in Figure 5.3 is zero (to two significant figures). 

The neutral rings react readily with radicals and other electron-deficient species, and a variety of reactions at surfaces are known. 

Neutral rings composed of an odd number of C—H groups have an odd number of electrons and hence cannot be closed-shell molecules. In study of odd-mem-bered rings, attention has focused on ions with even numbers of electrons, obtained by processes like those indicated in Equations 1.11 and 1.12. Rings containing a... 

Oxidation and reduction of all-carbon annulenes are known to result in cationic or anionic species with aromatic properties different from those of the neutral ring, offering a textbook example of the validity of Hiickel rules [87], hi pyrrole-containing porphyrinoids, such oxidations and reductions can be realized with retention of charge neutrality because the charge can be adjusted by protonation or... 

First, let us see how VB theory explains the symmetry properties of 4n versus An + 2 electronic systems in neutral rings. Consider a ring involving 2N atomic p orbitals, labeled from 1 to 2N, (3 in Scheme 5.1) and having one... 

A number of coal-derived liquids were examined by cyclic-voltammetry and other electrochemical techniques and found to show some activity. At anodic potentials films form on glassy carbon electrodes. It is suggested that this film formation is caused by oxidative coupling of radical cationic species with neutral ring structures through a mechanism similar to that which causes charring and coking in coal conversion processes. 

Neutral rings Monocations Dications Ring derivatives... 

Benzo derivatives, such as the benzo[l,3]dithiolium tetrafluoroborate 35 <2004JME5265>, are also known. For polycyclic systems that are isoconjugate with dianions, neutral rings with two oxygen/sulfur atoms, such as the cyclopenta[l,2]dithiole 36 , can be made. The occurrence of bicyclic systems with a bridgehead sulfur, such as the trithiapentalenes 37, should also be noted <1971AHC(13)161>. 

Draw one canonical form for each of the following aromatic compounds a three-membered carbocyclic cation with 2 electrons (n=0, 3 p sub-orbitals) a five-membered carbocyclic anion with 6 electrons (n= 1, 5 p sub-orbitals) and a six-membered neutral ring containing one nitrogen atom and five carbon atoms (n= 1, 6 p sub-orbitals). 

In case of neutral ring systems with an odd number of centers there exists only one Kekul6 structure without charge separation, in contrast to neutral and even membered rings. 

---