Molecular g Values and Paramagnetic Susceptibility in Pi-Bonding Systems: Vinylidene Fluoride

The first-order molecular Zeeman effect is observed in vinylidene fluoride to yield the molecular g values along the principal inertial axes. The results are | gaa | = 0.0373 ± 0.002, | gbb | = 0.0480 ± 0.003, and | gcc | = 0.0064 ± 0.003 where the a axis passes through both carbon nuclei and the b axis is in the molecular plane. The negative (positive) molecular g values and the molecular structure are used to give the diagonal elements in the paramagnetic-susceptibility tensor. The results are χaap = 103 (89) × 10−6, χbbp = 108 (92) × 10−6, and χccp = 217(212) ± 10−6 all in ergsG−2·mole−1. These values are compared with the recent corresponding numbers in H2CO, F2CO, H2C2O, and H2CF2. A molecular-orbital theory of paramagnetic susceptibility is employed to interpret the paramagnetic susceptibility in the H2CO, H2C2F2, F2CO, H2C2O, and H2CF2 molecules. A detailed discussion is given concerning the molecular orbitals participating in the n→π* transition in H2CO.