what terms refers to two structurally dissimilar molecules with the same molecular formulascience

In general, the term "isomer" is used to describe two
molecules with different structures and the same molecular formula.  However,there are a
variety of  supplemental terms used, depending on the type of dissimilarity between the
two molecules.

1. Structural or constitutional isomers
refer to two compounds of different types. For example, the formula C2H6O could be
ethanol (C2H5OH) or methyl ether (CH3OCH3).

2. In compounds
where there is a double bond present, there can be geometric isomers.  They have the
same structure, but one molecule has two groups on the same side of the double bond
while the other molecule has the two groups on opposite sides of the double bond. These
are denoted as "cis" or "trans" isomers.

3. Two molecules
with identical structures may exist as mirror images of each others. If this is true,
they are referred to as "enantiomers".

4. Some molecules,
without a double bond, may have different 3-D shapes or arrangements and these are
referred to as "diastereomers".