Question

please explain this point

Answer 1

Here in the above molecule the CH3 group is attached to 2,3,and 5 carbon that is why it will not be 2,4,5 because on 4th position ch3 is not attached there..
hope it will help u
plzz thumps up

Answer 2

It simply means that while naming the compound, you have to number the branches in a way that the sum of those numbers should be the least.

Like in the given example, if we start counting from left to right then we get the branches at 2, 4 and 5 respectively. Their sum is 2+4+5 = 11.

But if we count from right to left then the branches occur at positions 2, 3 and 5. Their sum is 2+3+5 = 10.

As 10 is less than 11, so we have to number them as 2, 3, 5.

Hope this helps.