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2023sponding tzg orbitals on each metal atom, then, gives three Fe-Fe bonds, one Q and two T .Concerning the evaluation of the Fe-Fe bond order in this compound, we are in agreement with Cotton' that any attempt to find a direct correlation of the metal-metal distance with bond order in this type of structures is meaningless. Therefore, it does not seem unreasonable to affirm that in the [FezH3(P3)z]+ complex cation there are three Fe-Fe interactions, some or all of which are weaker than a full bonding interaction.

The analysis of the pmr spectrum of cyclooctanone-2,2,7,7-d4 at -160°p rovides two values of geminal coupling constants: 2J = -11.0 and -16.0 Hz. The least negative value is associated with the methylene protons on C(2) of the BC conformation (1) and demonstrates unambiguously that the prediction of the Barfield-Grant relationship is wrong in the vicinity of = 120°a nd, further, provides an order of magnitude for the positive contribution to 2J from a carbonyl group predicted by molecular orbital calculations. The angular dependence of 2J is discussed in light of these results.

cis‐4‐Octen‐1,7‐diin (I) liefert mit tert.‐Butylat unter Annahme der Allen‐ Zwischenstufe (II) und weiterer Cyclisierung zu den tautomeren Formen (III) die beiden Dimeren (IV) und (V).

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