Alkenes and other compounds with C sp2 —Cl bonds

The C—Cl bond in chloroethylene [173.0(4) pm] is by about 4-5 pm shorter than the C—Cl bond in chloromethane. This difference is larger than that between the covalent radii of sp2 and sp3-hybridized carbon (74 and 77 pm, respectively). The C—Cl bond distances 

TABLE 26. C—Cl bond distances (in pm) in ethylenes and other compounds with C(sp2)—Cl bonds 

Several chlorinated 1,3-butadienes have been investigated in the gas phase with the primary interest in the influence of chlorination on the conformational properties. In the dichloro derivatives the C—Cl bond distances vary by about 2 pm, depending on the positions of the chlorine atoms. C—Cl bonds which eclipse a geminal C—H bond, such as in 23, are shortest [172.4(2) pm], C—Cl bonds which eclipse the central C—C bond in 24 are intermediate [173.1(3) pm] and C—Cl bonds which eclipse a C=C double bond are longest 

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