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Stereoisomers are isomers that differ in atom spatial arrangement rather than atomic connection order.

Definition of diastereomers-

If one of the asymmetric centres has the same configuration in both stereoisomers and the other asymmetric centre has the opposite configuration in both stereoisomers, stereoisomers with two asymmetric centres are called diastereomers.

There are four stereoisomers in a molecule having two chiral centres, such as 1-bromo-2-methylcyclopentane.

There are two asymmetric centres in 1-bromo-3-methylcyclohexane. The carbon that is connected to a Br and a H is also bonded to two distinct carbon-containing groups (—Because (—CH₂CH(CH₃)CH₂CH₂CH₂— and —CH₂CH₂CH₂CH(CH₃)CH₂—), the carbon connected to a CH₃ and a H is also bonded to two separate carbon containing groups, it is an asymmetric centre as well.

Both the cis and trans isomers have diastereomers that can be drawn. The four stereoisomers are all chiral.