Dipole moment nitro group

Compare the geometry of para-nitroaniline to those of both aniline and nitrobenzene. Is there any evidence for push-pull resonance contributors Is there shortening of bonds to the amino and nitro groups Are the bonds in the ring localized Is the dipole moment for para-nitroaniline smaller, larger or about the same as the sum of the dipole moments for aniline and nitrobenzene What does your result say about the importance of push-pull resonance contributors ... 

TABLE 16. Selected structural parameters of die nitro group (bond lengths in A, bond and torsional angles in degrees, dipole moments in Debye) for the set of nitro compounds used in die parameterization of MM2 and MM3 as obtained by the two force fields and... 

The conformation 325 with the axial nitro group and both R groups equatorial has been shown to predominate for 325 (R = benzyl and R = cyclohexyl) by dipole-moment measurements293,294 and Jgtm values are in accord with this.295 For the related diethyl compound, a low-temperature ( — 63°C) H-NMR spectrum shows 326 as the major conformer (A2ai,2eq 1.31 ppm) in equilibrium with 327 (A2ai 2eq 106 ppm).296... 

Eliel et a/.268 seem to confirm the observation that the nitro group in this type of heterocyclic system is preferred in the axial position. Katritzky et a/.269-271 have found on the basis of dipole moment measurements that tetrahydro-l,3-oxazines without a 5-nitro group have V-alkyl in the preferred equatorial position, although the axial N-CH3 and -C2H5 are important minor contributors (42 and 32%, respectively). 

We started the analysis of the sulfonyl group as an acceptor with the calculation of 4-methylsulfonylaniline (I), which is an analogue of p-nitroaniline (II), and their methylated derivatives (III, and IV, respectively). We have found that while the ground state dipole moments are comparable for the nitro and sulfone derivatives (Table I), the p coefficients are different in magnitude, and depend on the method of calculation (Table I). 

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