so in this lecture we're going to briefly revisit the concept of isomers now isomers are compounds that have identical molecular formulas but they differ in structures now isomers can be subdivided into two categories structural isomer also known as constitutional isomers and stereo isomers so let's begin by looking at structural isomers now structural isog are compounds that have the same molecular formula but different conductivity of atoms so let's look at one example of a structural isomer so this is a hydrocarbon it's composed of five carbons and 12 H atoms now both of these compounds have this molecular formula so they have identical molecular formulas but notice that the top Compound has a five five carbon backbone while this compound has a four carbon backbone one of the atoms has been removed from this position and placed on the second carbon so there is a difference in connectivity but we have the same exact molecular formula so these are known as structural isomers so now let's have a look at stereo isomers these guys are compounds that are the same exact molecular formula and the same connectivity but they differ in the arrangement of atoms in space now two types of stereoisomers exist we could subdivide this into en anomers and dumers so an anomers are nons superimposable miror images of one another so let's look at one such example so here we have a stereogenic carbon attached to four different groups if we take the mirror image of this compound we get a different compound so compound a and compound B and these differ in the arrangement of atoms and they're mere images of one another they're not superimposable and we know these guys as anomers now damers are all compounds other than in anomers so all compounds that are not mere images of one another and a few examples exist so cyrans or Ze isomers are example of dumers so number two confirmational isomer so Eclipse confirmation or stagger confirmation of a compound these are dumers also meso compounds meso compounds are ayal compounds that have stereogenic carbons these are all examples of the stereomers now stereo isomers and isomer these two words are usually used interchangeably but you should know the difference there's a big difference because isomers can be subdivided into stereo isomer as well as structural isomer so stereo isomer are isomer and isomer or an example of an isomer is stereoisomer but it's not the only one that exists there are also structural isomers that are not stereo isomers