Coupling constants alcohols

H and 13C NMR Data. The examples in Scheme 3.23 provide characteristic proton and carbon chemical shift and coupling constant data for fluorinated alcohols, ethers, thioethers, sulfoxides, and sul-fones. An ether substituent serves to deshield the carbon of a CH2F by about 20 ppm. This can be compared to the 40-ppm deshielding generally observed in a nonfluorinated ether system. Thus, the fluorine substituent seems to have a damping effect on the usual effects of other substituents. 

Table 12. CH-CH Shifts and Coupling Constants of the Tartaric Ester Moiety of 0,0 -Diacyltartaric Acid Esters of ac-Amino Alcohols with Rigid Ring Structure (d, DMSO-rf6)...

Table4. Vicinal H, H Coupling Constants in Diastereomeric P-Alkoxy, /1-Amino and / -Fluoro Alcohols OH OH...

The vicinal H,1SF coupling constants in the fluoro alcohols (Table 4) are 12-14 Hz in the syn- and 14-17 Hz in the ann-diastereomers 36°. There is no obvious explanation for this sequence, which is opposite to that of 3/HH. 

Only when the rate of alcohol exchange is lowered by cooling is the nonequivalence of fluorine atoms evident in the NMR spectrum. These exchange effects are observed because at room temperature the chemical shift between fluorine atoms in the two environments is comparable to the exchange rate. Chemical shiftsf and coupling constants of nuclei in molecules are comparable to the rates of many chemical processes. Consequently this possible complication must always be kept in mind. Exchange phe-... 

The 1II NMR corroborates diis conclusion since two vinyl protons are observed both in the reactant and product however, a new two-proton doublet appears at 4.155 for die newly produced allylic methylene group. The acid O-H proton is moved far upheld as well. The coupling constants of die vinyl protons (./ = 16 Hz) show the starting compound to be dans, and die large splitting for the downheld vinyl doublet of die product (J = 16 Hz) shows die trails stereochemistry to be maintained in die unsaturated alcohol product. Moreover die splitting between the methylene group and the upheld vinyl proton clearly supports its allylic position. 

The NMR spectrum of the cis-fused quinolizidol (64a) and its derivatives showed the presence of an equilibrium mixture of conformers where the form with an axial OH and equatorial phenyl group was only a minor component. The signal of H-l in 64b-d appears at <5 4.0-4.1 ppm as a triplet with a coupling constant of 4-5 Hz and W1/4 of 13-14 Hz. H-3 was in part unresolved from H-l in 64a,e and in 64c,d was a broad multiplet (a triplet of triplets with J 8-9 and 4.5 Hz) with W1/4 equal to 25-28 Hz. These couplings of H-l and H-3 favor that conformation with an axial phenyl and an equatorial hydroxyl. Compound 64a was synthesized by reduction of cis-fused quinolizidone (65b) with NaBH4 to yield mixture of 64a and its epimer in 1.3 1 ratio or with lithium tri-sec-butylborohydride, where 65% conversion to axial alcohol was observed. 

An enol ether type of vinyl group is present in ethyl vinyl ether, a reagent used for the protection of alcohols. This time all the coupling constants are smaller because of the electronegativity of the oxygen atom, which is now joined directly to the double bond. 

Data from NOE experiments nicely supplement information from coupling constants in the determination of three-dimensional stereochemistry loo. Reduction of this bicyclic ketone with a bulky hydride reducing agent gives one diastereoisomer of the alcohol, but which Irradiation of the proton next to the OH group leads to an NOE to tlie green proton. 

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