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CH3CH2CH CH3CCH3 CH3CH2COH CH3COCH3 ... WHICH ONE OF THE FOLLOWING IS AN ALDEHYDE STRICTURE?
The first one structure is aldehyde, (an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center (a carbon double bonded to oxygen) bonded to hydrogen and an R group, C2H5 in your case).