Geminal coupling constants and

Both the geminal coupling constant and the chemical shift difference of the 1-methylene group are indicative of the predominance of the tram-fused (+)- -4a,5a-H-perhydro[l,3]oxazino[3,4-6]isoquinoline f u predominance... 

In compounds of the type F2C=CXY, a linear correlation between F-F geminal coupling constants and fluorine chemical shift has been found. It has been ascribed to a change in the density of the nuclear spin information carrying electrons to the intervening carbon atom due to valence bond resonance structures such as F2C -CF=CF-0 . 

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