Diazo compounds geometry

Calculations on the 4-aminobenzenediazonium ion were also carried out by Alcock et al. (1980a) using ab initio and MINDO/3 techniques. They came to the conclusion that both methods have poor predictive value for the geometry of an ion of such complexity. However, two other semiempirical methods, namely MNDO (Dewar and Thiel, 1977) and AM-1 (Dewar et al., 1985), were applied with better results to a similar, but even more complex, zwitterionic diazo compound, 2-diazonio-4,6-dinitrophenolate, by Lowe-Ma et al. (1988 see 4.4 in Sec. 4.2). 

Diazo compounds can often be isolated, although many intramolecular cycloadditions occur at room temperature. Thus, the diazo compounds have typically been treated as reactive intermediates. Both 1,3-cycloaddition and 1,1-cycloaddition reactions have been observed, depending on the substrate geometry. 

The molecular geometries and the frontier orbital energies of heterophospholes 28-31 were obtained from density functional theory (DFT) calculations at the B3LYP/6-311- -G, level. The 1,3-dipolar cycloaddition reactivity of these heterophospholes in reactions with diazo compounds was evaluated from frontier molecular orbital (FMO) theory. Among the different types of heterophospholes considered, the 2-acyl-l,2,3-diazaphosphole 28, 377-1,2,3,4-triazaphosphole 30, and 1,3,4-thiazaphosphole 31 were predicted to have the highest dipolarophilic reactivities. These conclusions are in qualitative agreement with available experimental results <2003JP0504>. 

The Wolff rearrangement has been very successfully used in the synthesis of propellanes.40 The highly strained 3-diazo[3,2.2]propellan-2-one was photolyzed in dichloromethane at — 70 °C in the presence of dimethylamine to give A W-dimethyl tricyclo[2.2.2.0 u4]octane-2-carboxamide (5), a very highly strained interesting compound with inverted geometry at the bridgehead carbons,42 in 40% yield.41... 

The isolation of pyrinoderains (43-46) was followed by the discovery of a new bicyclic 3-AP from the sponge Cribrochalina sp. [20]. This compound, pyrinadine A (47), Fig. (11), possesses an unprecedented azoxy moiety in the middle of the alkyl chain. The geometry of the diazo double bond was deduced to be Z from the UV absorbance maximum, and its position was established by ESI MS/MS analysis on 47 and on its reductive degradation product. 

The vast majority of diazo (generically C—N=N) compounds studied by X-ray diffraction involve extensive delocalization through unsaturated groups involving the C atom. Very few diazoalkanes or azidoalkanes have been reported and even here the canonical forms contributing to the effective resonance hybrids involve considerable electron delocalization. For these reasons, the geometries of diazo and azido compounds for all types of substitution are covered in Section III.B.4. 

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