Refers to the benzene ring, the 1 position is allyl, the 4 th position is bromine, and the 2 nd position is chlorine.
After determining the location of 1, write down the location of 23456. The structure diagram is as follows.
The kind we often see.
This is called structural simplification, so don't confuse it.
The structural formula is to write all atoms, and the structural simplification can be omitted.
Regarding the benzene ring, there must be a number 1, and the serial number after 1 is determined. The first number is the number. Then look at what substituents are written after the corresponding numbers and write them down. For example, this 1- allyl -4- bromo -2- chlorobenzene means that 1 is followed by allyl, No.4 is followed by bromine and No.2 is chlorine.
The college entrance examination may give this naming structure, but if you give a structural name, it will be at most two substitutions on the benzene ring, and there will be no three substitutions.