Follower ring

The kinetics of this type of polymerization are the same as for simple condensation for this reason, the use of the term polycondensation is perhaps more appropriate. Unless kinetic evidence suggests otherwise, polymerizations involving the formation of chain polymers from cyclic compounds, following ring scission, are classed as condensation polymerizations. Some important con-... 

Thomson fOV Click Organic Interactive to learn to recognize the most stable conformations of cyclohexanes following ring-flips. 

Prostaglandins belonging to die PGFa group have the following ring structure ... 

Draw the most important Lewis structure for each of the following ring molecules (which have been drawn without showing the locations of the double bonds). Show all lone pairs and nonzero formal charges. If there are equivalent resonance... 

In a research program to explore the possibilities of synthesizing useful polymeric materials from silazane (Si-N) containing ring compounds, reactions of the following ring systems were studied ... 

For numerous [5,5] (2Nl)-compounds, mass spectra data have been included in their spectral characterization. Mostly the molecular ion has been given, and in some cases fragments have also been assigned. Only few reports contain a complete analysis these include the following ring systems ... 

Click "Next" to see the following ring (the rings appear in the same order in which the program has detected them. This order cannot be predicted). At any moment you can click "Cancel" to leave out the rings which have still not come up. In the upper left part of this dialog box you can check how many rings out of the total number have been seen. 

Product concentrations as a function of the contact time suggested the following ring closure pathway of heptadiene over chromia (22) ... 

The reaction of cyclobutanone oxime 277 with S2GI2 affords the conjugated 1,2-thiazine 70 in 45% yield (Equation 38) <1996JOC9178>. The proposed mechanism for this transformation involves the intermediate nitrile 278, which reacts to form imino-disulfide 279. Following ring contraction of 279 and further chlorination, product 70, whose structure was confirmed by X-ray analysis, is obtained. 

In the great major tiy of applications that use the intramolecular nitrile oxide-alkene cycloaddition, the intention is to prepare intermediates for the synthesis of natural products or related compounds. The most popular transformations of these isoxazolines are the following ring cleavage modes ... 

The l,3,4-oxadiazin-6-one (240) undergoes cycloaddition followed by a remarkable rearrangement to give the triazole A(-imine 241 and an open-chain product (136). Cycloadditions have also been carried out with the following ring systems 1,2-dihydroisoquinoline (242) (137) dihydro-1,3-oxazine (243) (138,139), 2H-, 3-benzothiazine (244) (140,141), and 27/-l-pyran-2-thione (245) (142). 

Exercise. Compute the marginal and conditional probabilities for the following ring-shaped bivariate distribution ... 

On the basis of these assumptions it can be said that the first ring present in the molecule contains six carbon atoms and each following ring adds four carbon atoms to this number. 

A rather unique synthetic example based on the well-known pyrrole-pyridine carbene insertion reaction involves the following ring expansion.16... 

It was demonstrated by Coughlin (16) that formaldehyde catalyzed the N-nitrosation of 1,3-thiazolidine at pH 7. Therefore, it is possible that HCHO catalyzed the formation of N nitroso-1,3-thiazolidine in these reactions, presumably following ring closure. 

We have observed that diol 3, cis-2-butene-l,4-diol, and cis-1,2-bis(hydroxymethyl)cyclohexane react smoothly with TPP-CClq to afford 4 (78%), 2,5-dihydrofuran (65%), and cis-8-oxabicyclo[4.3.0]-nonane 84%). Reaction of diol 5 with TPP-CCli in CH3 CN gives 52% of 5-chloropentanol, 6 (11%), and 1,5-dichloropentane (25%) while diol 7 affords 6-chlorohexanol (48%) and 1,6-dichlorohexane (39%). Comparisons of the ether chlorohydrin dichloride product distributions arising from these simple diols reveal a trend for efficiency of chain closure to 3 - 7 membered rings where the formation of cyclic ethers appear to decrease in order of the following ring size 3-5>6>4-7. 

Ring formation by reaction of N-nucleophiles onto carbonyl groups is well established and continues to be reported. For example, reductive amination following ring opening of the diol 56 gave the azasugar 57 (Equation 193)... 

Note that the use of the colon in (9) indicated the subordination of the following rings to the central one, whereas the semicolon in (13) indicates the independence of these rings. Also, the final semicolon in (13) represents the continuation (back to the beginning) of the super-cycle. 

Propose a mechanism for the following ring-opening transesterification. Use the mechanism in Problem 21-13 as a model. 

Other ring transformations giving isoxazoles (or isoxazolines capable of conversion into isoxazoles) are as follows ring expansion of oxirans41 and oxetanones42 ring contraction of pyrimidines, pyrimidinium salts, pyrimidine JV-oxides,43 pyrylium salts,44 ketonylidenepyrans,45 chromones, thiochromones, chromylium salts,46-51 and oxazinones 52 photoisomeriza-... 

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