Heterocycles, inorganic

Both colourless and deeply coloured compounds are found among the common unsaturated heterocyclic inorganic systems. For example, borazine B3N3H6 (see Section 4.1.2.1), like benzene, is a colourless liquid which exhibits a strong absorption band in the UV region. Similarly, cyclophosphazenes (NPX2) ( = 3-6 X = halogen, alkyl, aryl, alkoxy, dialkylamino) are also... 

Heteroboranes, structure prediction for. 802-807 Heterocatenation. 741-742 Heterocyclic inorganic ring systems, 775-780 Heterogeneous catalysts, 705 Heteronuclear diatomic molecules. molecular orbitals in, 167-175... 

Heterocycles, inorganic, 9, 329-348 a-Heterodiazoalkanes, 9, 397-429 Homogeneous catalysis and oxidative addition reactions, 7, 84-90 Hydrocarbon-metal ir complexes, 10, 317-321... 

Chapters V-X deal respectively with Heterocyclic and Alicyclic Compounds Miscellaneous Reactions Organic Reagents in Inorganic and Organic Chemistry Dyestuffs, Indicators and Related Compounds Some Physiologically-Active Compounds and Synthetic Polymers. Many of these preparations are of course intended for advanced students, but a mere perusal of the experimental details of selected preparations by those whose time for experimental work is limited may assist to impress them on the memory. Attention is particularly directed to the chapter... 

Addition compounds form with those organics that contain a donor atom, eg, ketonic oxygen, nitrogen, and sulfur. Thus, adducts form with amides, amines, and A/-heterocycles, as well as acid chlorides and ethers. Addition compounds also form with a number of inorganic compounds, eg, POCl (6,120). In many cases, the addition compounds are dimeric, eg, with ethyl acetate, in titanium tetrachloride-rich systems. By using ammonia, a series of amidodichlorides, Ti(NH2) Cl4, is formed (133). 

Heterocyclic Alcohols. Thek reactions with chloroformates lead to carbonates. Thus furan- and tetrahydrofuran-derived alcohols give the corresponding carbonates in 75% yield (15). Inorganic bases and tertiary amines as acid acceptors increase the rate and yield in this reaction. 

H.G. Heal, The Inorganic Heterocyclic Chemistry of Sulfur, Nitrogen and Phosphorus, Academic Press, London (1980). 

T. Chivers, Sulfur-Niti ogen Heterocycles, in I. Haiduc and D. B. Sowerby (ed.) The Chemistry of Inorganic Homo- and Heterocycles, Vol. 2, Academic Press, London, pp. 793-870 (1987). 

A. W. Cordes, R. C. Haddon and R. T. Oakley, Heterocyclic Thiazyl and Selenazyl Radicals Synthesis and Applications in Solid-State Ai chitecture, in R. Steudel (ed.) The Chemistry of Inorganic Heterocycles, Elsevier, pp. 295-322 (1992). 

The criterion of ipsocentric ring current has been used to assess aromaticity in S-N heterocycles (and related inorganic ring systems). Current density maps indicate that the ten r-electron systems [SsNs], [S4N3] " and [S4N4] ", and the fourteen r-electron system [S5N5] " support diatropic k currents, reinforced by a circulations. 

I. Haiduc, The Chemistry of Inorganic Ring Systems, Part 2, (sulfur-nitrogen heterocycles), pp. 909-83, Wiley, London, 1970. 

What are the details of the reaction mechanism for inorganic aromatic heterocycles While we are still arguing about aromatic substitutions, we wish to add this new challenge for future investigations. 

Comprehensive Inorganic Chemistry (1973) Comprehensive Organic Chemistry (1979) Comprehensive Organometallic Chemistry (1982) Comprehensive Heterocyclic Chemistry (1984) International Encyclopedia of Education (1985) Comprehensive Insect Physiology, Biochemistry Pharmacology (1985) Comprehensive Biotechnology (1985)... 

Keywords Chemical orbital theory, Cw-stability, Cyclic conjugation. Disposition isomers. Diradicals, Donor-acceptor, Electron delocalization, Geminal bond participation, Inorganic heterocycles. Ring strain. Orbital phase. Orbital phase continuity. Polarization, Preferential branching. Reactivity, Selectivity, Stability, Tautomerism, Z-selectivity... 

Almost all known inorganic heterocychc molecules, where N, O and S atoms with lone pair orbitals are donors while B atoms with vacant p orbitals are acceptors, are classified into discontinuous conjugation. The donors and the acceptors are alternately disposed along the cyclic chain. The thermodynamic stabilities are controlled by the non-cycUc electron delocalization or by the number of neighboring donor-acceptor pairs, but not by the number of % electrons [83]. In fact, both 4n % and 4n + 2% electron heterocycles are similarly known [84,85] (Scheme 33), contradicting the Hueckel rule. 

Scheme 33 Known inorganic heterocycles containing N and B atoms...

Keywords Valence electron rule, Metal ring, Metal cluster, AN +2 valence electron rule, 8/V +6 valence electron rule, 6N +14 valence electron rule, Pentagon stability, Cyclopentaphosphane, Hydronitrogen, Polynitrogen, Triazene, 2-Tetrazene, Tetrazadiene, Pentazole, Hexazine, Nitrogen Oxide, Disiloxane, Disilaoxirane, 1,3-Cyclodisiloxane, Metallacycle, Inorganic heterocycle... 

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