Fig.1

Oxalic acid (ethanedioic acid)

Fig.2

Malonic acid (propanedioic acid)

Fig.3

Succinic acid (butanedioic acid)

Fig.4

Glutaric acid (pentanedioic acid)

Fig.5

Adipic acid (hexanedioic acid)

Fig.6

Maleic acid (cis-2-butenedioic acid)

Fig.7

Fumaric acid (trans-2-butenedioic acid)