Question

CH3 - CH( CH3) - CH2 - CH( OH ) - CHO​

Answer 1

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Longest carbon chain has to be chosen such that the functional group has the lowest number.

So we start numbering from the carbon of aldehydic group (−CHO). Thus there are 5 carbon is the longest chain.

At C-2 ethyl group and at C-3 position methyl group is present. The suffix used for aldehydes is "al".

Therefore, the IUPAC name is: 2-Ethyl-3-methyl-pentanal.