Isomerguide - enantiomers (HINT: look for chiral C atom(s)...

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How to determine the relationship between molecules There are different types of isomers. Below are a set of guidelines for how you determine the relationship between molecules: Question 1 : do all molecules have the same molecular formula? If the answer is NO, then those are different molecules & you don’t need to go on. If YES , then the molecules are isomers & you need to determine what type of isomers the molecules are go on to question 2. Question 2 : are all the atoms connected in the same way? If the answer is NO, then the two molecules are constitutional (or structural) isomers . For example C 2 NClH 6 can go together like this CH 3 H 2 N Cl H OR H 2 CN H CH 3 Cl If the answer is yes, then the two molecules are either 2 versions of the same molecule or stereoisomers , but there are different types of stereoisomer so, go on to question 3: Question 3 : are the two molecules mirror images of one another (that cannot be simply rotated to get the same molecule) (also ask if one is R- and the other is S)? If yes
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Unformatted text preview: enantiomers (HINT: look for chiral C atom(s) and check that there is NO plane of symmetry in the molecule you are looking at watch out for meso compounds-the molecule has a chiral centers AND a plane of symmetry). For example: CH 3 H 2 N Cl H and CH 3 Cl NH 2 H If no then the molecules are diastereomers . Diastereomers are stereoisomers that are not mirror images of each other & go on to question 4. Question 4 : Do the molecules differ in the spacial placement of groups around a double bond or a ring? If yes, then the molecules are cis-/trans- isomers (or geometric isomers) . For example for C 2 NClH 4 : H NH 2 Cl H or NH 2 H Cl H Trans- Cis- Question 5: is there more than 1 chiral center? If yes , then the molecules are (configurational diastereomers) diastereomers also include molecules that contain more that one chiral center (more than 1 chiral C atom). For example sugars: CHO OH H H OH H OH OH H HOH 2 C and CHO OH H H OH OH H OH H HOH 2 C...
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This note was uploaded on 02/13/2011 for the course CHEM 2344 taught by Professor Slack,wu during the Spring '11 term at University of Houston.

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