Which compound is LESS stable?

[mnnob07]

below are two simple compounds. this is from a first semester general chemistry test and there were four compounds total all with the same number of C H and O we had to tell which one was least stable and why.

I don't remember the other two because both had a formal charge of 0 on everything while these two had a +1 on the O (most of the time not a good sign) and -1 on the C.

I picked the first one as less stable because of the formal charges and because I was used to seeing the hydrogen atoms bonded to the C.

Can anyone tell me if I was right and what is the best way to approach these problems aside from straight formal charges?

 

[GCT]

Does the top carbon have a hydrogen on it? Please make sure that all structures have the right numbers of hydrogen.

 

[mnnob07]

What do you mean? notice that there are two structures separated by a bit of whitespace. The top structure has no hydrogens on the carbons. Would you like me to draw the lone pairs?

 

[mnnob07]

I drew the lone pairs on the top one:

 

[GCT]

This problem is a test of your understanding of the concept of oxidation states - there a rules in calculating these values and it does involve considering the formal charge - oxidation states also takes into account the type of atoms that a particular central atom is bonded to as well as its bonding arrangement while formal charge takes into account soley the bonding arrangement of the particular atom.