To observe a significant change in the polaritonic ground state (due to the non-resonant light-matter coupling terms in the Hamiltonian), it generally requires a very strong light-matter interaction strength between a single molecule and the cavity mode. This light-matter coupling regime can be realized by using state-of-the-art plasmonic nano-cavities, which provide realistic experimental parameters that were used for these simulations. In these systems, the cavity mode volume is extremely small, on the order of Å3 . For example, a recent nano-cavity achieved a mode volume 50 of V = 0.15 nm 3 . The coupling strength typically required 20 to observe any interesting changes to the ground state is λ = 1/εV ≈ 0.1 a.u. corresponding to A 0 ≈ 0.3 a.u. or field strength E = 10.8 V/nm that can be experimentally accomplished Experimentally, the NanoParticle on Mirror (NPoM) cavity structure 51 can achieve such coupling strengths with electric field intensities E = ω c A 0 ≈ 2-10 V/nm. For the specific case of a gold plasmonic nano-cavity, the cavity frequency is ω c = 1.8 eV.These coupling strengths from NPoM cavities are also consistent with a mode volume of V = 0.15 nm 3 . Fig. presents the relative energetic stability of the meta-and ortho-cationic intermediate species, computed as E ortho 0 (R) -E meta 0 (R) inside the cavity, as a function of θ and ϕ. Fig. presents the results of E para 0 (R) -E meta 0 (R). The cavity polarization direction ê with respect to the X, Y, and Z directions of the molecule is defined by the polar angle θ and the azimuthal angle ϕ (see Scheme 1a(ii) and the inset of Fig. ). In Fig. all possible spatial orientations of the cavity polarization direction ê with respect to the molecule are presented. When θ = 90 • and ϕ = 0 • (or equivalently ϕ = 360 • ), ê = X and when θ = 90 • and ϕ = 90 • , ê = Ŷ .