H-bond distances

Take C—H bond distance and bond strength for example Recalling that an elec tron m a 2s orbital is on average closer to the nucleus and more strongly held than an... 

Figure 4 shows the measured angle of 105° between the hydrogens and the direction of the dipole moment. The measured dipole moment of water is 1.844 debye (a debye unit is 3.336 x 10 ° C m). The dipole moment of water is responsible for its distinctive properties in the Hquid state. The O—H bond length within the H2O molecule is 0.96 x 10 ° m. Dipole—dipole interaction between two water molecules forms a hydrogen bond, which is electrostatic in nature. The lower part of Figure 4 (not to the same scale) shows the measured H-bond distance of 2.76 x 10 ° m or 0.276 nm. 

Structure. Ethylene is a planar molecule with a carbon—carbon bond distance of 0.134 nm, which is shorter than the C—C bond length of 0.153 nm found in ethane. The C—H bond distance is 0.110 nm, and the bond angles are [Pg.432]

Figure 6-20. Bond dissociation curve showing that the average R-H bond distance is greater than the R-D bond distance because of their zero-point energy difference.

Because of anomalous scattering by H the results for the as-precipitated Ni(OH)2 could not be refined. Nevertheless, cell constants and the O-H bond distance could be determined. The results showed that the as-precipitated material was different from the well-crystallized material. The unit cell dimensions were aQ =3.119 and c0 =4.686 A. Also the... 

Cyclopropane gave photographs showing four rings, with qualitative appearance corresponding closely to the calculated curve of Fig. 4. The s0 and I values given in Table V lead to the radial distribution curve shown in Fig. 3 (curve A), with peaks at 1.12 A. (C-H bond distance), 1.52 A. (C-C bond distance) and 2.2-2.5 A. (larger C-H... 

The intensity curves I, II, III, and IV of Fig. 4 are calculated for coplanar trans models with C-H = 1.06 A., the angle H - C=C = 115°, and the angle H—C—H = 109.5°. Although these hydrogen parameters are so chosen as to agree as well as possible with minor peaks of the radial distribution function, no great reliance can be placed on them, and indeed it is likely that for this molecule the C-H bond distance is 1.09 A. The models have the following additional parameters... 

Indications are that a C—D bond is slightly shorter than a corresponding C—H bond. Thus, electron-diffraction measurements of C2H6 and showed a C—H bond distance of 1.1122 0.0012 A and a C—D distance of 1.1071 0.0012... 

The isolated iron hydride complexes introduced in this chapter are listed in Table 12, where the hydride chemical shifts in the HNMR spectra and the Fe-H bond distances are summarized. 

Eshmate the optimum H-bonding distance corresponding to the calculated energy optimum via Eq. (14),... 

Table 12-2. Experimental values and deviation from experiment of the R0 H bond distance, the symmetric (vs) and the antisymmetric (vas) stretching frequency [cm-1], the dipole moment [D], and the mean polarizability [A3] of the water molecule. The aug-cc-pVTZ basis set is used throughout. 

The hard sphere exclusion distances for this system were chosen as follows nonbonded backbone carbons, 4.60 R (twice the C-H bond distance plus van der Waals radius for H) non-neighboring fluorines, 2.70 R (twice van der Waals radius for F) neighboring fluorines, 6.39 R (distance across phenyl ring using dimensions of Table I and van der Waals radius for Hof... 

Still, the reasons for this success were not quite clear for instance, the good performance of the method in reproducing the equilibrium C—H bond distance in methane was thought to depend on fortuitous cancellation of the nuclear repulsion and of the change in... 

Compounds C—H bond distances C=C bond distances ZCCH angles... 

FIGURE 23.2 Profiles of (a) energy and FF values for nucleophilic attack and (b) for electrophilic attack for distortion in the N-H bond distance of ammonia. 

Concomitant with the change in the oxygen coordination number is a shift of the first minimum of the O-H RDF from 1.30 A at 34 GPa to 1.70 A at 115 GPa. We observe a similar structural change in the H-H RDF in which the first peak lengthens from 1.63 A (close to the result for ambient conditions) to 1.85 A. These observations bear a strong resemblance to the ice VII to ice X transition in which the covalent O-H bond distance of ice becomes equivalent to the hydrogen bond distance as pressure is increased.82 However, the superionic phase differs from ice X, in that the position of the first peak in g(RoH) is not half the distance of the first 0-0 peak.82 We analyze the effect... 

---