CONFORMATION-DEPENDENT EFFECTS OF THE NITRO-GROUP UPON SOME STRAINED TERTIARY C-C BONDS

Computational studies (SCF-MO, 3-21G) have shown that an NO2 substituent can have a weakening effect on strained tertiary C-C bonds, depending upon its conformation relative to these bonds. This is particularly significant when the C-C-N plane is perpendicular to that of the NO2. The weakening is greatly reinforced when an NH2 group is on the other carbon of the C-C bond; indeed, the "perpendicular" conformer of aminonitrotetrahedrane was found to undergo a rearrangement to 1-amino-3-nitrocyclobutadiene. This does not happen for the corresponding monoaza system nor does any significant bond weakening take place in the unstrained nitroethane and 1-amino-2-nitroethane molecules. An orbital correlation analysis of nitrotetrahedrane has shown that the bond-weakening effects can be interpreted in terms of interactions between a -type NO2 orbital and the C-C bonding orbitals. 1990 American Chemical Society.

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