Carbon sp3 hybrid orbitals

FIGURE 7.7 The bonding in methane. Each of the four C-H bonds results from head-on (singly occupied carbon sp3 hybrid orbital with a singly occupied... 

Tetrahedral displacement of carbon sp3 hybrid orbitals which overlap withhydrogen Is orbitals. 

The structure of ethane. The carbon-carbon bond is formed by a- overlap of two carbon sp3 hybrid orbitals. (For clarity, the smaller lobes of the sp3 hybrid orbitals are not shown.)... 

The concept of hybridization explains how carbon forms four equivalent tetrahedral bonds but not why it does so. The shape of the hybrid orbital suggests the answer. When an 5 orbital hybridizes rvith three p orbitals, the resultant sp3 hybrid orbitals are unsyimmetrical about the nucleus. One of the two... 

When we discussed sp3 hybrid orbitals in Section 1.6, we said that the four valence-shell atomic orbitals of carbon combine to form four equivalent sp3 hybrids. Imagine instead that the 2s orbital combines with only two of the three available 2p orbitals. Three sp2 hybrid orbitals result, and one 2p orbital remains unchanged- The three sp2 orbitals lie in a plane at angles of 120° to one another, with the remaining p orbital perpendicular to the sp2 plane, as shown in Figure 1.13. 

It will thus be apparent why the use of hybrid orbitals, e.g. sp3 hybrid orbitals in the combination of one carbon and four hydrogen atoms to form methane, results in the formation of stronger bonds. 

Figure 1.11 Hybridization of pure atomic orbitals of a carbon atom to produce sp3 hybrid orbitals. 

Carbon atoms (1) and (4) use sp3 hybrid orbitals to form four sigma bonds, three by overlap with the hydrogen Is orbitals and one by overlap with an sp2 orbital from the central carbon (2). The two carbon atoms involved in the double bond undergo sp2 hybridization. They form C-H bonds by overlapping with Is orbitals of the H atoms. The C=C double bond is formed similarly to that described in (a). 

In dimethyl ether, the oxygen atom is sp3 hybridized. In creating two single bonds, each bond is formed by the overlap of one of its sp3 hybrid orbitals with the sp3 hybrid orbital on the adjacent carbon atom. Each of the remaining two hybrid orbitals on the oxygen atom contain a lone pair of electrons. The resulting molecule is polar. The intermolecular forces found operating between molecules of dimethyl ether are therefore dipole-dipole interactions and London forces. 

In this case since carbon has only two unpaired electrons, it seems likely that it will only form only two covalent bonds, but it is known that carbon can form four covalent bonds. To form four bonds, one electron is promoted from the 2s orbital to the 2pz orbital. Then the one 2s orbital and three 2p orbitals mix together to form four new sp3 hybrid orbitals as shown in Figure 5. So in this case of hybridization, three p and one s orbital combine to give four identical sp3 orbitals. 

Figure 5 Energy changes during the formation of the sp3 hybrid orbitals in a carbon atom.

The carbon atom (6C) has the electron configuration of ls22s22p2. There are 4 valence electrons, of which only two are unpaired in the ground state. During the formation of carbon compounds, one 2s and three 2p orbitals combine to give four identical sp3 orbitals by the promotion of an electron from the 2s orbital to a 2p orbital. These 4 unpaired orbitals then mix to form four identical sp3 hybrid orbitals. 

Carbon undergoes hybridization and forms four identical sp3 hybrid orbitals. 

For example, in the methane molecule (CH4), the four sp3 hybrid orbitals of the carbon atom overlap end to end with one Is orbital from each hydrogen atom to form four C — H bonds. Those bonds are all o bonds. 

Similarly, C — H sigma bonds in the C2H6 molecule are formed by the end to end overlap of sp3 hybrid orbitals of the carbon atoms with the Is orbitals of the hydrogen atoms. The C—Co bond is formed by the end to end overlap of the sp3 hybrid orbitals of the C atoms. So in the C2H6 molecule there are six C — H o bonds and one C—Co bond making seven o bonds in total. 

The lowest unfilled molecular orbitals in the haloalkanes are formed from the out-of-phase overlap of an sp3 hybrid orbital of the carbon atom... 

The platinum(II)-ylide bond involves donation of a pair of electrons in a formally sp3 hybrid orbital on carbon to an empty orbital on platinum(II). The short bond lengths and XPES spectroscopy suggest some multiple bond character. 

FIGURE 2.8 sp3 Hybridization (a) Electron configuration of carbon in its most stable state, (b) Mixing the s orbital with the three p orbitals generates four sp3 hybrid orbitals. The four sp3 hybrid orbitals are of equal energy therefore, the four valence electrons are distributed evenly among them. The axes of the four sp3 orbitals are directed toward the corners of a tetrahedron. 

FIGURE 2.10 The C—C a bond in ethane, pictured as an overlap of a half-filled sp3 orbital of one carbon with a half-filled sp3 hybrid orbital of the other. 

Ethylene is planar with bond angles close to 120° (Figure 2.15) therefore, some hybridization state other than sp3 is required. The hybridization scheme is determined by the number of atoms to which carbon is directly attached. In sp3 hybridization, four atoms are attached to carbon by ct bonds, and so four equivalent sp3 hybrid orbitals are required. In ethylene, three atoms are attached to each carbon, so three equivalent hybrid orbitals... 

Bonding in methane is most often described by an orbital hybridization model, which is a modified form of valence bond theory. Four equivalent sp3 hybrid orbitals of carbon are generated by mixing the 2s, 2px, 2py, and 2pz orbitals. Overlap of each half-filled sp3 hybrid orbital with a half-filled hydrogen Is orbital gives a cr bond. 

The carbon-carbon bond in ethane is a cr bond in which an sp3 hybrid orbital one carbon overlaps with an sp3 hybrid orbital of the other. 

An orbital hybridization description of bonding in methylamine is shown in Figure 22.2. Nitrogen and carbon are both sp3-hybridized and are joined by a a bond. The unshared electron pair on nitrogen occupies an sp3-hybridized orbital. This lone pair is involved in reactions in which amines act as bases or nucleophiles. The graphic that opened this chapter is an electrostatic potential map that clearly shows the concentration of electron density at nitrogen in methylamine. 

---