Question

For butane,write condensed structural formula for an isomer which has only primary and secondary carbon atoms and another isomer which has one tertiary carbon atom?

Answer 1

Since butane has only 4 carbon atoms there are only two possible isomers.

Explanation:

Put all C's in a row and you get butane, also called n-butane. This one has two end-atoms (=primary) and two in-betweens (=secondary).
Condensed this would be `CH_3CH_2CH_2CH_3` or just `C_4H_10`

Put three in a row and attach the fourth to the middle one and you get iso- butane, or officially (2-)methyl propane. This one has three end-atoms (=primary), and one that is attached to three others (=tertiary).
Condensed this could be: `CH_3CH(CH_3)CH_3` or even:
`CH(CH_3)_3`

When drawing, you fill up the empty C-valences with H's.