Table 1: Viability of the different proton and neutron combinations.

Cisphasic # (reactive ends in phase)Transphasic × (reactive ends out of phase)

Two protons
p # p
Notviable
Two protons
p × p
Viable

Two neutrons
n # n
Notviable
Two neutrons
n × n
Viable

Proton joined to neutron
p # n
Viable
Proton joined to neutron
p × n
Notviable