The structure and energetics of the ring isomers of C4n+2 (n=3–5) carbon clusters were studied by using coupled-cluster singles and doubles excitation theory to overcome the vast differences existing in the literature. The results obtained in the present study clearly indicate that C14, C18, and C22 carbon rings have bond-length and bond-angle alternated acetylenic minimum energy structures. Contrarily, density functional theory calculations were unable to predict these acetylenic-type structures and they ended up with the cumulenic structures. It is found from the coupled-cluster studies that the lowest-energy ring isomer for the first two members of C4n+2 series is a bond-angle alternated cumulenic D(2n+1)h symmetry structure while the same for the remaining members is a bond-length and bond-angle alternated C(2n+1)h symmetry structure. In C4n+2 carbon rings, Peierls-type distortion, transformation from bond-angle alternated to bond-length alternated minimum energy structures, occurs at C14 carbon ring.