N—H bond length

The parent compound of all amines, ammonia, has a pyramidal structure with N—H bond lengths of 101.5 pm and H—N—H bond angles of 106.6°. The electronic structure of the ground state may be represented as... 

The stretching of the N-H covalent bond in N-H—O systems, involving N-H bond lengths of 0.95-1.10 A, is not very significant (Figure 5), in comparison with the O-H—O system, 0.85-1.20 A (Figure 3) or in comparison with experimental error. The reason for the small variation in N-H bond lengths is probably that there are no or few exactly-matched structures reported in the CSD. We noted a difference... 

Figure 5. N—H bond lengths in N—H O hydrogen bonding systems. The phenomenon of N—H bond stretching is only weakly represented (if at all), probably because there are only few nearly matched systems that have been characterized by neutron diffraction. Neutron diffraction data are from the CSD. From top to bottom all N—ammonium-carboxylate, ApKa 5 neutral heterocycle-...

Potential, N-H Bond Length, and Inverse Vibration Frequencies as Functions of Intrinsic Reaction Coordinate for Inversion of the Ammonia Molecule... 

Let us now work out the representation of a point group for a very simple basis. We will choose just the changes, Ar, and Ar2, of the two N-H bond lengths of the diimide molecule, N2H2 (4-1). 

Figure 4-7. The four symmetiy operations of the C2h point group applied to the two N-H bond length changes of the HNNH molecule.

The diimide molecule (4-1) is our example again, and the basis is the two N-H bond length changes (see Figure 4-7). It is easy to generate the matrices corresponding to each operation using such a simple basis however, even this may not be necessary. As mentioned before, instead of the representations themselves, we can work with their characters. For this particular case the characters of the representation have already been determined ... 

Returning to the diimide N-H bond length changes, let us see how the above simple rules work. The identity operation, A, leaves... 

Table 3.5. Riding motion and anharmonicity corrections for C-H and N-H bond lengths in the neutron diffraction analyses at 15 K of deuterated benzene [203], thioacetamide [204], and 1,2,4-triazole [199]...

Figure 2.3 N-H bond length as a function ofN - H bond length for a series of accurately determined neutron structures. fR < 0.06, only N-H - N bonds with no additional contacts are included in the analysis.)...

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