O∣∣CH3−C−CH3\qquad \quad O \\ \qquad \quad \mid \mid \\ \mathrm{CH}_{3}-\mathrm{C}-\mathrm{CH}_{3}O∣∣CH3−C−CH3
C6H5−CHO\mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{CHO}C6H5−CHO
H−COOH\mathrm{H}-\mathrm{COOH}H−COOH
CH3−CO\mathrm{CH}_{3}-\mathrm{CO}CH3−CO