Enantiomers are stereoisomers that are non-superimposable mirror images of one another.
Some compounds with two stereogenic centres are not optically active due to symmetry planes
If there are two stereogenic centres, one half of the molecule is the mirror image of the other half.
The mirror images are non-superimposble because the compound is asymmetric (has no symmetry planes or centres).
In compounds with two stereogenic centres, the enantiomer has the opposite configuration at all stereogenic centres.
The first two structures in the diagram below show trans-1,2-dichlorocyclohexane and its mirror image.
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In compounds with two stereogenic centres, the enantiomer has the opposite configuration at all stereogenic centres.
The first two structures in the diagram below show trans-1,2-dichlorocyclohexane and its mirror image.
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The third structure is included to show that the mirror image is not superimposable as would be expected for a pair of enantiomers.
Some compounds with two stereogenic centres are not optically active due to symmetry planes
If there are two stereogenic centres, one half of the molecule is the mirror image of the other half.
These are referred to as meso forms. The cis dichlorocyclohexanes shown below are all meso forms.
The diagrams show that these compound and its mirror image are in fact the same due to the configuration at the stereogenic centres being opposite.
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