Tetrahedral bond angle

Like alcohols, ethers have nearly the same geometry as water. The R-O-R bonds have an approximately tetrahedral bond angle (112° in dimethyl ether), and the oxygen atom is 5p3-hybridized. 

Furthermore, spz bonding is connected with tetrahedral bond angles (as in Figure 16-11). These expectations are consistent with the experimentally determined structure of diamond, shown in Figure 17-2. 

Although we have described the structures of several molecules in terms of hybrid orbitals and VSEPR, not all structures are this simple. The structures of H20 (bond angle 104.4°) and NH3 (bond angles 107.1°) were described in terms of sp3 hybridization of orbitals on the central atom and comparatively small deviations from the ideal bond angle of 109° 28 caused by the effects of unshared pairs of electrons. If we consider the structures of H2S and PH3 in those terms, we have a problem. The reason is that the bond angle for H2S is 92.3°, and the bond angles in PH3 are 93.7°. Clearly, there is more than a minor deviation from the expected tetrahedral bond angle of 109° 28 caused by the effect of unshared pairs of electrons ... 

An instructive illustration of the effect of molecular motion in solids is the proton resonance from solid cyclohexane, studied by Andrew and Eades 101). Figure 10 illustrates their results on the variation of the second moment of the resonance with temperature. The second moment below 150°K is consistent with a Dsi molecular symmetry, tetrahedral bond angles, a C—C bond distance of 1.54 A and C—H bond distance of 1.10 A. This is ascertained by application of Van Vleck s formula, Equation (17), to calculate the inter- and intramolecular contribution to the second moment. Calculation of the intermolecular contribution was made on the basis of the x-ray determined structure of the solid. 

Answer. Nitrogen undergoes sp hybridization, not sp, so it is tetrahedral. The additional sp orbital is occupied by a lone pair of electrons from the nitrogen. This lone pair results in electron-electron repulsion that causes the other sp orbitals bonded to fluorines to be closer together than the normal 109° tetrahedral bond angle, hence the 107.3 F-N-F bond angle. 

Additional differences are noted in the EPR spectra of these two complexes (Fig. 9). The g anisotropy in the EPR spectra is different for the two complexes in spite of very small differences in their tetrahedral bond angles (Fig. 7). The EPR spectrum for the protein (15) does not have the excellent resolution of that of the model complexes and further studies may be necessary to demonstrate quantitative similarities between the model complexes and the enzyme-Co2 + complex. 

Fig. 3—15 show four-, five- and six-atom chains (A—C -2—B) in their non-planar staggered conformations (dihedral angles of 60° and 180°). The individual bond conformations are denoted P (positive), M (minus), consistent with the proposals of Cahn, Ingold and Prelog 15>, and T (trans), as shown in 4. Using the familiar properties of triangles and the tetrahedral bond angle (cos r = — 1/3) (see Ref. 12 for the derivation of the equation in Fig. 3) we have derived expressions for the subtended areas (A) as needed for use with the helical conductor model (Eq. (1)). It turns out that all of these expressions contain the term L... 

With tetrahedral bond angles and staggered conformations ... 

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