Question

Why is PROPANONE the first member of Ketons???

Answer 1

HEY MATE HERE IS YOUR ANSWER--

The first member of Ketones is  (IUPAC name) 2 - propanone.   H3C - CO - CH3.    This is also called Acetone.

Ketone series of Organic compounds have the group CO in them between two groups that contain Carbons.

  The Carbonyl group is in the center.  The structure of Ketones is as follows:

          O

          ||

    R - C - R'

      H        O     H

       |         ||      |

H - C  -     C  -  C - H

      |                  |

     H                 H

Q) WHY PROPANONE IS FIRST MEMBER OF KETONE??

The ketone group lies in between. Since methanone would only contain 1 carbon atom - no such compound exists, the first compound with a susbstitued ketone group is thus propanone. This conversation is already 

Answer 2

Because ketons have double bond O with a carbon somewhere in middle of the compound.

So you cant put it with one carbon because.

If you put it with two carbons it becomes ethenal as aldehyde has double bond O with the last carbon of the compound.

So the next choice is with three carbons which becomes propanone