Stereochemistry and NMR Spectra

The configurations of chiral thiiranes and thiirane 1-oxides can be determined by H NMR experiments in chiral solvents such as (R)-(-)- -phenyl-2,2,2-trifluoroethanol. The 

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The experimental observation of stereochemistry. It is worth pointing out some of the characteristics of the relationship between stereochemistry and NMR spectra which arise from the examples described. These practical considerations must be borne in mind when approaching the interpretation of a spectrum in terms of stereochemistry. 

In a few cases, the stereochemistry of adducts has been elucidated from their vibrational and NMR spectra. The arrangement in compound (IV) has already been displayed, the product of the reaction in entry 30 is known to be (V) (223) [and this is confirmed by an X-ray study of the GeMe3 analog (202)], while the product in entry 33 is (VI) (229). The adduct Ph3SiMnH(CO)2(Cp) (entry 4) adopts a piano-stool... 

The planar structure, except the geometry of a C8 double bond, was initially proposed shown in Fig. (9) by the detailed analysis of ID and 2D NMR (COSY, HMQC and HNBC) data and by comparison of its and NMR spectra with those of structurally related compounds such as aerothionin (18), purealin (19) and others [30-41]. Although the DQF-COSY spectrum of 17 showed few H- H correlations, the HMBC spectrum was very useful for elucidating the planar structure of 17. The geometiy of C8 double bond was elucidated by a NOESY H7 /NH correlation to be trnas. The relative stereochemistry of 17 was clarified by... 

Anomaline (57), demethoxyanomaline (58), and 12-O-methylanomaline (59) are three new alkaloids related to aspidocarpine, which have been extracted from the bark of Microplumeria anomala (M. Arg.) Mgf., collected from the banks of the Rio Negro (72). These structures were deduced mainly by analysis of their proton and NMR spectra, and by comparison of their NMR data with those of appropriate models again, structures 57-59 show only the relative stereochemistry. 

Phytochemical studies on Narcissus obesus have resulted in the isolation of a new alkaloid named obesine (420) (see Fig. 24), accompanied by several known Amaryllidaceae alkaloids (74). The stereochemistry and structural determination of the alkaloid 420 have been carried out by spectroscopic analyses and by application of 2D NMR techniques. Although the H-6)8 proton (5 4.38) is masked by the H-3 proton (5 4.30-4.40), the H-6a proton (54.02) was assigned at higher field on the basis of the nuclear Overhauser effect (NOE) with H-12 endo (5 3.10) observed in the 2D NMR experiment. On the other hand, the a disposition of H-3 was confirmed by the NOE between H-3 (5 4.30-4.40) and H-12 exo (5 3.01). In the C-NMR spectrum of 420 a characteristic signal due to the C-11 carbon was observed at 82.7 (singlet) ppm. Also, a comparison of the H and NMR spectra of obesine (420) with those of the related alkaloid 3-epi-marconine (303) (50) was performed. 

Securinol C, isomeric Avith both securinol A and B 57), exhibited IR, UV, and NMR spectra consistent with a hydroxylated dihydro-securinine formulation (5S). Treatment of securinol C with methanesul-fonyl chloride in pyridine gave allosecurinine (Section II, D). Thus securinol C is a 14,15-dihydroallosecurinine-type alkaloid with a hydroxyl group located at C-14 or C-15. The latter possibility (C-15-OH) was excluded by showing that securinol C was not enantiomeric with either of the two possible 14,15-dihydroviroallosecurinine alkaloids, securinol A and B. Further examination of the NMR and mass spectra of securinol C provided evidence for the assignment of structure and partial stereochemistry 163 to securinol C. 

The stereochemistry was assigned from the and NMR spectra. Reductive elimination of acetone showed first-order kinetics, with EHt = 25.0 kcal moU and A5 f = 5.3 calK moUT ... 

There are a number of reports on the synthesis of the saturated ring system, and NMR spectra were used to determine the structure. In some cases, the stereochemistry has been established by spectroscopic analysis <90JOC2254>. Some 0x0 derivatives, such as (97), have been studied by attached proton test (APT) and heteronuclear shift correlation (HETCOR) experiments <9lJOC858>. Pyrrolidine ring conformation in two 2,3-dioxoperhydropyrrolo[l,2-c]imidazoles were analyzed from H NMR data using a generalized Karplus equation <85BSB187>. 

Stereochemistry of the Rhodium Hydride and Rhodium Methyl Complexes. On the basis of IR and proton and NMR spectra, all of the cationic hydrides [Rh(ttp)HCl(L)] (where L = CO, CH3CN, C2H5OH) and [Rh(ttp)HBr(CO)] are six-coordinate whereas the methyl cation [Rh(ttp)CH3Cl] can be isolated as the five-coordinate species as well as the six-coordinate compounds [Rh(ttp)CH3Cl(L)] (L = CH3CN, CO). 

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