High n (=50-250) molecular Rydberg states are characterized by a high density (rho proportional to n(3)/2Ry) of electronic stales and by unique intramolecular couplings (V) which involve long-range Rydberg electron-core multipole interactions. We explore spectroscopic and dynamic implications of the dipole coupling V = C-D(nn’)(-3/2) of a doorway Rydberg state n,1,N+,N] with a dense {n’,1’,N+-1,N]} manifold (n’> n) of bound Rydberg states, which are described by Hund coupling case (d). We establish the conditions for the realization of the statistical limit (V rho >> 1 and gamma rho < 1) and of the sparse mixed level structure (V rho >> 1 and gamma rho << 1) within the mixed electronic manifold (where gamma = Gamma(0)/n(3) are the nonradiative decay widths). The statistical Limit for an electronic quasicontinuum is realized for the coupling strength domain 1.109Ry(B/Ry)(3/8) < C-D < (Gamma(0)Ry/pi)(1/2), establishing how the characteristics of the level structure and dynamics sue determined by the rotational constant B, by the molecular dipole moment (C-D proportional to mu), by the decay width constant gamma(0), and by l (where C-D proportional to l(-7)). The statistical limit within all electronic quasicontinuum is expected to be amenable for experimental, observation in polar large molecules, while the np(N+=0)-n’d(N+=1) coupling in H2O (Gilbert, R. D.; Child, M. S. Chem. Phys. Lett. 1991, 187, 153) corresponds to the sparse mixed level structure. Our analysis provides a generalization and unification of the theory of intramolecular coupling and dynamics for an electronic quasicontinuum.