Eight-ring Oxygen Compounds

A similar case90, this time with a rectangular distortion of the [SnS]2 geometry, is caused by weak coordination of 2N at each Sn in [(Me2NCH2CH2CH2)2Sn(Ph)S]2 to give irregular six-coordination at Sn. The two Sn-S distances are 244 and 248 pm and the two Sn... N values are 281 pm (trans to the shorter Sn-S) and 316 pm. The CSnC angle is 137° and SSnS is 93°. 

A fuller NMR study91 of exchange in [Ar2ES]2, for E = Sn, Pb, demonstrated redistribution over combinations of Ar and Sn or Pb. When the four-membered [BujSnSh was included in the exchange, mixed element products were identified with both four- and six-rings, such as [(Pt PbSXBujSnS) ] for x = 1 or 2. 

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All quantitative calculations are carried out by computer programs (2,6,16). Calibration data are at present available for 95 heteroaromatic compound types, including one-to-seven or -eight ring thiophenes, furans, mono- and dihydroxyaromatics, pyrroles, pyridines, and nitrogen/oxygen compounds. Semiquantitative data are available on an essentially unlimited number of additional heteroaromatics. 

In contrast to the 1,4-dithiocin system, 1,4-dioxocin (1) is well-known and has been characterized as an olefinic compound by its spectra as well as its chemical behavior.5-6 The reason why 1,4-dioxocin in contrast to 1.4-dihydro-1.4-diazocine (see Section 1.4.) and 4//-l,4-oxazocinc (sec Section 1.12.), does not qualify as a 107r-aromatic species, is the less pronounced tendency of oxygen atoms for 7t-electron delocalization. An X-ray analysis of the 6-substituted 1,4-dioxocin 2 confirms the presumed nonplanar conformation of the 1,4-dioxocin structural element.9 The eight-membered ring exhibits a twisted boat-chair confirmation. 

The transannular interaction in the eight-membered (and also in nine-membered) ring amino ketones decreases the oxygen (170) exchange rate with water, as shown by 170 NMR, which also reveals an unusually shielded 170 chemical shift in such compounds (72HCA907). 

In addition to our Investigation of oxygen reactions with carbanlone, we have also studied the reaction of sulfur on carbanlons. Sulfur exists naturally under the form of an eight membered ring Sg. Different authors have Introduced sulfur In organic compounds via various methods. 

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