Nuclear spin isomerism in molecules other than H2 I was reading my teacher's material about ortho- and para- hydrogen, and I found stated that 


  "every homonuclear molecule, with nuclides with spin other than zero ($\ce{H2}$, $\ce{D2}$, $\ce{T2}$, $\ce{N2}$, $\ce{^{17}O2}$...) has nuclear spin isomers".


What is not clear to me is: are there any nuclides with spin zero? Is there, hence, any homonuclear molecule without spin isomers?
Nucleons of the same type tend to pair up and cancel out each others' spins, so nuclides with an even number of protons and an even number of neutrons will have zero spin. Some common nuclides with this property include $^4\ce{He}$, $^{12}\ce{C}$, and $^{16}\ce{O}$.