The C-C -bond activation step can be understood in more detail through further consideration and analysis of transition state. In all cases, breaking of the M-C, and making of the M-C bond accompanies C  -C  bond activation. As a result, the C  =C  ---C  motif adopts an electronic structure reminiscent of an allyl ligand in the TS (Figure ). For example, TS-2 when M = Mg and n = 1 has a short C=C bond length of 1.42 Å, stretched C-C bond of 1.94 Å, and even, near symmetric, Mg-C and Mg-C distances of 2.22 and 2.26 Å respectively. Charge localisation occurs across the allyl moiety, but primarily at the terminal carbons, C (-1.01) and C (-0.94), rather than C (-0.18). AIM calculations capture bond paths between both C and C with Mg, but not between C and C in the breaking bond. Wiberg Bond Indices from NBO provide a similar picture of electron distribution in this TS, with partial double bond character in the C=C unit (1.42) and a weakened C---C bond (0.57).