Ethane, bond angles structure

The structural features of methane ethane and propane are summarrzed rn Ergure 2 7 All of the carbon atoms have four bonds all of the bonds are srngle bonds and the bond angles are close to tetrahedral In the next sectron we 11 see how to adapt the valence bond model to accommodate the observed structures... 

FIGURE 2 7 Structures of methane ethane and propane showing bond distances and bond angles... 

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]

The bond angles are also satisfactorily reproduced in most of the cases. This is also true for dihedral angles which are sometimes more accurately predicted than by the use of the larger, double-zeta sets. For instance, experimental evidence favors the gauche structure for 1,2 difluoro ethane. STO-3G calculations lead to a gauche structure, while 4-31G calculations predict a trans structure. 

Ball-and-stick models of organic substances provide a convenient means of studying the structures of various organic compounds. Balls with holes represent the atoms, and sticks represent the covalent bonds. Figure 1-3 shows two conformations of ethane in which the dark balls represent carbon and the light balls represent hydrogen. All bond angles are the normal 109.5°. 

Bond Distances, Bond Angles, and Bond Energies in Ethane, Ethene, and Ethyne (Table 9.1, p. 342) Structures of a-Amino Acids (Table 27.1, pp. 1054-1055)... 

Most molecules can avoid high-energy, sterically-hindered structures by distorting their geometries in some way. Compare the CC and CH bond distances, and the HCC bond angle, of fully staggered and eclipsed ethane. Which, if any, of these parameters undergoes distortion in order to relieve steric repulsion in the eclipsed molecule Explain. 

The three-dimensional structure of ethane, C2H6, has the shape of two tetrahedra joined together. Each carbon atom is sp3 hybridized, with four sigma bonds formed by the four sp3 hybrid orbitals. Dashed lines represent bonds that go away from the viewer, wedges represent bonds that come out toward the viewer, and other bond lines are in the plane of the page. All the bond angles are close to 109.5°. 

Structures for the two simplest acyclic alkanes were given in Chapter 1. Methane, CH4, has a single carbon atom, and ethane, CH3CH3, has two. All C atoms in an alkane are surrounded by four groups, making them sp hybridized and tetrahedral, and all bond angles are 109.5°. 

This quantum mechanical structure of ethylene is verified by direct evidence. Electron diffraction and spectroscopic studies show ethylene (Fig. 5.4) to be a flat molecule, with bond angles very close to 120 The C—C distance is 1.34 A as compared with the C—C distance of 1.53 A in ethane. 

The structure of the ethane molecule illustrates further the structural principles mentioned in the discussion of the methane molecule and the diamond crystal. The carbon-carbon bond length is 1.54 A, as in diamond, and the carbon-hydrogen bond length is 1.10 A, as in methane. The H—C—H and H—C—C bond angles have been found by experiment to have the regular tetrahedral value 109.5° to within the experimental uncertainty, about one-half a degree. 

The structure of the normal butane molecule, /1-C4H10, is shown in the adjacent drawing. (The prefixed letter n in the formula is the abbreviation for normal.) The bond lengths and bond angles have the same values as in ethane. The zigzag chain of carbon atoms and the positions of the hydrogen atoms correspond to the stable (staggered) orientation about each of the four carbon-carbon bonds. The n-butane molecule thus presents us with no surprises. 

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