Torsion of the NH2 group

TABLE 6. Basis set dependence of calculated geometries of vinylamine (115) with (planar (119) and pyramoidal amino groups rotated out of the vinylic plane by 90° (120 and 121). Distances in A and angles in deg 

In the case of the +90° rotated pyramidal NH2 group, 120 and 121, the C=C distance is elongated only by 0.0008 A from ethene in 120 where the nitrogen lone pair is outside and shortened by 0.0008 A in 121 when the nitrogen lone pair is inside. 

The two bonds C2—H1 and C2—H2 at / -carbon in Table 6 are now very similar, but shorter than those of ethene in the corresponding basis set except in the case of 

The C2CXN angle is about 123.8° for the rotated planar amino group of 119 and is increased to 126° for 120 and decreased to 122° for 121, which has the nitrogen lone pair inside. The H4NH5 angle is reduced from 118° to 107° on rotated pyramidalization (120 and 121) which is less than the value of 112° calculated for coplanar pyramidalization in 117. 

Experimentally, free enthalpies of activation (AG n) corresponding to rotational barriers around C—N bonds of variously substituted enamines have been obtained from a linear correlation, represented by equation 7. This was derived from a relation of the 

FIGURE 3, Rotational barriers (in kcal mol ) of vinylamine calculated with use of the 6-31G basis set from values presented in Table 9. is the angle between the orientation of the electron lone pair on N and the vinylic n-system 

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