Hybridization in ethylene

Section 2 20 Carbon is sp hybridized in ethylene and the double bond has a ct com ponent and a rr component The sp hybridization state is derived by mix mg the 2s and two of the three 2p orbitals Three equivalent sp orbitals result and their axes are coplanar Overlap of an sp orbital of one car bon with an sp orbital of another produces a ct bond between them Each carbon still has one unhybridized p orbital available for bonding and side by side overlap of the p orbitals of adjacent carbons gives a rr bond between them... 

Olah received the Nobel Prize in 1994 for proving its existence. Note that some textbooks still use erroneous nomenclature. Cations are very reactive, but can be stabilized by inductive or resonance effects. Resonance stabilization is illustrated in benzyl and allyl cations (Figures 1.6 and 1.7). The double bond in the ally lie cation is also in sp hybridization, with the p orbitals overlapping. Sp hybridization in ethylene is shown in Figure 1.8. 

Ethylene is planar with bond angles close to 120° (Figure 2 15) therefore some hybridization state other than sp is required The hybridization scheme is determined by the number of atoms to which carbon is directly attached In sp hybridization four atoms are attached to carbon by ct bonds and so four equivalent sp hybrid orbitals are required In ethylene three atoms are attached to each carbon so three equivalent hybrid orbitals... 

FIGURE 2 17 The carbon-carbon double bond in ethylene has a cr component and a tt compo nent The cr component arises from overlap of sp hybridized orbitals along the internuclear axis The tt component results from a side by side overlap of 2p orbitals... 

FIGURE 5 1 (a) The planar framework of u bonds in ethylene showing bond distances and angles (b) and (c) The p orbitals of two sp hybridized carbons overlap to produce a tt bond (d) The electrostatic potential map shows a region of high negative potential due to the tt elec trons above and below the plane of the atoms... 

FIGURE 17 2 Both (a) ethylene and (b) formal dehyde have the same num ber of electrons and carbon IS sp hybridized in both In formaldehyde one of the carbons is replaced by an sp hybridized oxygen Like the carbon-carbon double bond of ethylene the carbon-oxygen double bond of formaldehyde is com posed of a (T component and a TT component... 

The hybridization concept can also be applied to molecules containing double and triple bonds. The descriptive valence bond approach to the bonding in ethylene and... 

We conclude this introduction to hydrocarbons by describing the orbital hybridization model of bonding in ethylene and acetylene, parents of the alkene and alkyne families, respectively. 

Like the carbon atoms in ethylene, the carbon atom in formaldehyde is in a double bond and therefore sp2-hybridized. 

To illustrate this rule, consider the ethylene (C2H4) and acetylene (C2H2) molecules. You will recall that the bond angles in these molecules are 120° for ethylene and 180° for acetylene. This implies sp2 hybridization in C2H4 and sp hybridization in C2H2 (see Table 7.4). Using blue lines to represent hybridized electron pairs,... 

The double bond in ethylene contains one a bond and one 7r bond. The a bond forms from the end-on overlap of two hybrid orbitals, and the 7i bond forms from the side-by-side overlap of two atomic p orbitals. Figure 10-21 shows the complete orbital picture of the bonding in ethylene. Ethylene is the simplest of a class of molecules, the alkenes, all of which contain CDC double bonds. The alkenes are the subject of our Box on page 404. 

For example, for the most discrepant case in Table 3.2, the sp237 and sp1-44 hybrids for ethylene correspond, respectively, to 70% and 59% p character, rather than the expected 66%. 

Both carbon atoms in ethylene molecule undergo sp2 hybridization and form three identical sp2 hybrid orbitals. One p orbital remains unhybridized. Two sp2 hybrid orbitals from each carbon atom overlap end to end with the Is orbital of a hydrogen atom and four C — Ho bonds are formed in total. Also, between the two carbon atoms, a C — Co bond is formed as a result of the overlap between two sp2 hybrid orbitals. So, in the C2H4 molecule in total there are five o bonds. Meanwhile, the unhybridized p orbitals of the two carbon atoms overlap side by side and form a rt bond. So between the two carbon atoms in the C2H4 molecule there is one o bond, formed by the overlapping of sp2 hybrid orbitals and one n bond, formed by the side by side overlapping of the unhybridized p orbitals. In total, two bonds are formed, hence a double bond exists between the two carbon atoms. 

Since carbon of a carbonium ion is in an sp2 hybrid, the ion pair is planar with a vacant p orbital (as in ethylene) which is perpendicular to the plane of three covalent bonds to the carbon. 

Figure 10-4 shows the hybridization that occurs in ethylene, H2C=CH2. Each carbon has sp2 hybridization. On each carbon, two of the hybrid orbitals overlap with an s-orbital on a hydrogen atom to form a carbon-to-hydrogen covalent bond. The third sp2 hybrid orbital overlaps with the sp2 hybrid on the other carbon to form a carbon-to-carbon covalent bond. Note that each carbon has a remaining p-orbital that has not undergone hybridization. These are also overlapping above and below a line joining the carbons. 

The pATa of the hydrocarbon ethane is about 50, that of ethylene about 44, and that of acetylene is about 25. The hybridization of the C-H bond in ethane is sp (25% i character), in ethylene it... 

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