Microwave Spectrum, Molecular Structure of Vinyl Cyanide and a Summary of CC, CH Bond Lengths in Simple Molecules

The microwave spectra of six isotopic species of vinyl cyanide (acrylonitrile) CH2CHCN have been investigated. From the rotational constants it is shown that the molecule is planar, and has the following structural parameters (exclusive of the CH2 group): r s ( C ≡ N )=1.163 7 A ,r s ( C − H )=1.086 3 A , r s ( C − C )=1.425 6 A ,∠ C = C − C =122 ∘ 37 ′ , r s ( C = C )=1.338 9 A ,∠ H − C − C =121 ∘ 44 ′ . The quadrupole hyperfine structure was interpreted according to the asymmetric top treatment leading to a value of eqQ = —4.21±0.04 Mc/sec for the quadrupole coupling constant along the C≡N bond. A table of the most accurate published values of CC and CH bond lengths is included. A graphical presentation of these results shows that the C–C, C=C, and C–H bond lengths vary linearly with the number of adjacent bonds.