Chem3A Exam 2 StudyGuide Problems

Chem3A Exam 2 StudyGuide Problems - Midterm #2: Study Guide...

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Midterm #2: Study Guide This does not cover everything, but it covers most important concepts. Radical Halogenation: always has three main phases Initiation - start of the reaction; form 2 radicals from no radicals. Break a weak bond (e.g. O-O bond) CH 4 + Br 2 h (light) CH 3 Br + HBr Propogation - the chain-reaction part of the reaction; must regenerate the radical you start with Termination - the end of the reaction; form no radicals from 2 radicals. Br Br 2 Br H 3 C H Br H 3 C + HBr H 3 C Br Br H 3 CBr + Br Some Possibilities: H 3 C CH 3 H 3 CCH 3 start with Br , end with Br start with 2 radicals, end with no radicals H 3 C Br H 3 CBr Br Br Br 2 S e l e c t i v i t y : when there are different kinds of H's on the molecule, selectivity trend: 3 o H > 2 o H > 1 o H H b H a H a H a H a H a H a H a H a H a Br 2 , h Br + Br h a lo g e n ti o t H io b 1 major product Always bear in mind that if you make a stereocenter, consider all possible stereoisomers! Cl F Br 2 , h Cl Br F Cl Br F +
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Stereochemistry : definitions to know stereoisomers - molecules w/ identical connectivities, different orientations in space. Very general term. stereocenter - an atom with four different groups around it H CH 3 Br Cl - If you swap ANY two groups on the stereocenter, you make the opposite stereocenter. - If you move three groups, it's the same as swapping two and then swapping two - you get back the original stereocenter. - The best way to determine if molecules are enantiomers, diasteromers, or neither is to compare stereocenters directly. enantiomers - molecules that are non-superimposable mirror images of each other Me H F Cl Me H F Cl - From these rules, it follows that if a molecule has only 1 stereocenter, it has an enantiomer but no diastereomers. diastereomers - molecules that are stereoisomers but not enantiomers. require 2+ stereocenters. CH 3 NH 2 Cl CH 3 NH 2 Cl 2 stereocenters are the same, 1 is flipped chiral - a molecule/object whose mirror image is nonsuperimposable (e.g. your hands!) meso - a molecule w/ stereocenters but which is achiral; has an internal mirror plane M i s c e l l e n e o u s T i p s CH 3 NH 2 Cl CH 3 NH 2 Cl A B C A B C stereocenter A is flipped from molecule 1 to molecule 2. stereocenter B is identical from molecule 1 to molecule 2. stereocenter C is identical from molecule 1 to molecule 2. molecule 1
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Chem3A Exam 2 StudyGuide Problems - Midterm #2: Study Guide...

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