what is structural isomer? can you alos give me examples? thanks !
Draw the structure pentant (acutally it is n-pentane) out to see it.
CH3CH2CH2CH2CH3
H3C
    \
     CHCH2CH3
    /
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.
H3C
    \
     CHCH2CH3
    /
H3C
Hope this one looks better.
A structural isomer is a type of isomer, which means it is a compound with the same molecular formula but different structural arrangements or connectivity of atoms. In other words, structural isomers have the same atoms but are arranged differently.
For example, let's consider n-pentane (CH3CH2CH2CH2CH3). It is a straight-chain hydrocarbon with five carbon atoms in a row, with all the hydrogen atoms attached to them.
However, there are other isomers of pentane that have the same formula (C5H12) but different structural arrangements. One example is 2-methylbutane. In this isomer, the second carbon atom from the left has an additional methyl (CH3) group attached to it, branching off from the main carbon chain. The structure of 2-methylbutane is:
H3C
     \
      CHCH2CH3
     /
Another example is 2,2-dimethylpropane. In this isomer, both the second and third carbon atoms from the left have methyl (CH3) groups attached to them, resulting in a branched structure. The structure of 2,2-dimethylpropane is:
H3C
    \
     C(CH3)3
    /
These are just a few examples of structural isomers of pentane. By changing the way the carbon atoms are connected or arranging additional functional groups, you can create various structural isomers with the same molecular formula.