5) E-1,2-dihydroxyethylenetautomers of 3 (unstable - an equilibrium greatly prefers 3)
6) Z-1,2-dihydroxyethylene
4) 1,1-dihydroxyethylenetautomer of 1 - equilibrium prefers 1
3) 2-oxoethanalQuote5) E-1,2-dihydroxyethylenetautomers of 3 (unstable - an equilibrium greatly prefers 3)
6) Z-1,2-dihydroxyethyleneQuote4) 1,1-dihydroxyethylenetautomer of 1 - equilibrium prefers 1
7 and 10 extremely chemically unstable
but from formal point ovf view OK