posted by jay! .
what is structural isomer? can you alos give me examples? thanks !
Draw the structure pentant (acutally it is n-pentane) out to see it.
See (if this came out right--usually there is a spacing problem) that the first one has C-C bonds from right to left. However, in the second one, the first C has two CH3 groups attached to it with all the others being a "straight" chain. This an example of an structural isomer. Instead of having an extra CH3 group attached to the second carbon from the left we could attach it to the third carbon from the left and have another (and different) isomer. I hope this helps.
Not bad but I left an H3C group off the lower /. The revised structure looks like this.
Hope this one looks better.