The compounds ${\mathrm{CH}}_3\mathrm{CH}={\mathrm{CHCH}}_3$ and ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{CH}={\mathrm{CH}}_2$

are tautomers

are position isomers

contain same number of ${\mathrm{sp}}^3-{\mathrm{sp}}^3,{\mathrm{sp}}^3-{\mathrm{sp}}^2 \text{and }{\mathrm{sp}}^2-{\mathrm{sp}}^2$ carbon-carbon bonds

exist together in dynamic equilibrium