LAOCOON

Work on indazoles has the drawback of having to employ computer procedures to analyze the ABCDX system of C-unsubstituted indazoles. The first five examples in Table 9 correspond to LAOCOON-analyzed spectra and the last two to simpler systems for which the first-order analysis gives acceptable chemical shifts. 

Oxidation of dialkenyl disulfides gave the stereoisomeric 2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5-oxides 36 and 37, which are found in extracts of onion. Further conversion and oxidations afforded a series of various 2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane derivatives, which were characterized on the basis of the comparative X-ray structural and NMR and IR spectroscopic data. The 111 NMR peak assignments for 36 and 37 were facilitated by LAOCOON III analyses of these 10 spin systems and by examination of the shifts induced by Eu(fod)3 and d6-benzene (fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octadione) <1996JA2790>. 

The proton signals of uridine (36) dissolved in deuterium oxide are well separated at 220 MHz, and a complete analysis and simulation of the spectrum by means of the LAOCOON II computer program (see Section V, p. 74) has been reported.107 It was concluded from the temperature-independence of the coupling constants and chemical shifts of the D-ribofuranoid moieties of uridine, /3-pseudouridine (40), and a-pseudouridine (41), that each of these compounds... 

The probable errors of the refined chemical-shifts and coupling-constants are printed in the output of the LAOCOON programs, but these errors are now generally believed246 to be unreasonably small, and they have sometimes been multiplied by a factor of two248 or five247 when reported. 

The LAOCOON II program has been used to calculate theoretical spectra for l,3,4,6-tetra-0-acetyl-2,5-0-methylene-D-mannitol-1,1,6,6-d4 (76 p. 73),192 and in the iterative analysis and simulation of spectra of methyl 2,3- and 3,4-anhydroglycopyranosides86 (LAOCN3 was also used), the protons of the sugar portion of many nucleosides,104-105-107 109 for example, 2 -deoxyadenosine251 (84), and adenosine 5 -phosphate126 (55 p. 60). 

C-satellites), and trans 2-arylcyclo propanecarboxylic acids (44, Ar = various substituted benzene rings, LAOCOON II). 

The reaction of methyl 1/7-azepine-l-carboxylate with A,a-diphenylnitrone yields [2 -I- 3] dipolar cycloaddition products (28) as a mixture of exo- and e /o-isomers <92H(34)497>, the structures of which were assigned with the aid of LAOCOON III simulated NMR spectra. The almost equal distribution of isomers at C5 and the absence of any tra 5-product favors a concerted 1,3-dipolar addition rather than the involvement of a stepwise ionic mechanism, since in a stepwise reaction the conformational flexibility of the azepine ring would allow the second bond to be formed on either face of the azepine ring. 

This similarity aided assignment IH (4), the aromatic proton closest to the heteroatom and so most affected by Its replacement, can be assigned to the hlgh-fleld doublet LAOCOON simulation then confirms that H (3)... 

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