¹³C^-13C coupling constants in derivatives of trans‐stilbene and tetraphenylethylene. Determination of relative signs II

Magnitudes and signs of 13C-13C coupling constants in compounds of the type Ph13CR1R2-13CR1R2Ph have been determined and the results are discussed in a broader context. Two types of coupling constants, J(C‐i, C‐α) and J(C‐i, C‐β), between aromatic carbon atoms and the benzylic carbons, probably with different coupling mechanisms, are considered. Whereas 2J(C‐2, C‐α) are always found positive, 2J(C‐1, C‐β) in the present compounds are found to be negative or about zero. 3J(C‐3, C‐α) has the same sign as 2J(C‐2, C‐α). A 4J and a 5J were observed in trans‐stilbene.