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

Abstract

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): $$\begin{array}{c}{r}_s(\mathrm{C}\equiv \mathrm{N}{\text{)=1.163}}_7\hspace{0.17em}\mathrm{A}{\mathrm{,r}}_s(\mathrm{C}-\mathrm{H}{\text{)=1.086}}_3\hspace{0.17em}\mathrm{A},\\ r_s(\mathrm{C}-\mathrm{C}{\text{)=1.425}}_6\hspace{0.17em}\mathrm{A}\mathrm{,\angle }\mathrm{C}=\mathrm{C}-\mathrm{C}{\text{=122}}^{\circ }{37}^{\prime },\\ r_s(\mathrm{C}=\mathrm{C}{\text{)=1.338}}_9\hspace{0.17em}\mathrm{A}\mathrm{,\angle }\mathrm{H}-\mathrm{C}-\mathrm{C}{\text{=121}}^{\circ }{44}^{\prime }.\end{array}$$ 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.