Structures involving two double bonds or a triple bond

The BF3 molecule is also planar with F—B—F angle of 120°. If we assume that only six electrons are involved, the structure is understandable because the repulsion between the bonded pairs is minimized in this configuration. However, it is isoelectronic with C03 ion so we might regard it as a compound with CO3 structures of the type 

8 STRUCTURES INVOLVING TWO DOUBLE BONDS OR A TRIPLE BOND 

If we hybridize only the s and 2p orbitals (sp hybridization) we obtain two sp hybrids, and I2, which are oppositely directed along a straight line (Fig. 23.15a). The electron configurations for the species of interest are 

The simplest example of the triple bond is in the nitrogen molecule illustrated in Fig. 23.15. Two 7C bonds are formed in addition to the o bond. The unshared pairs are 180° from the sigma bond on each end of the molecule. The formation of two n bonds results in the charge cloud having the shape of a cylindrical sheath around the axis of the molecule. (Compare to Fig. 22.5 for m = 1.) Species that are isoelectronic with nitrogen and therefore have the same electronic structure are C=0, C=N, and C=C.  

In the acetylene molecule, both carbon atoms are hybridized in this way. The cr bond and n bonds are shown in Fig. 23.16. The formation of two n bonds yields a cylindrical 

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Structures Involving Two Double Bonds or a Triple Bond 549... 

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