Chemistry 210: Chapter 2, Lectures 8, 9, and 10
Chemistry 210: Chapter 2, Lectures 8, 9, and 10 CHEM 210
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This 3 page Class Notes was uploaded by Julianna Sickafus on Sunday September 18, 2016. The Class Notes belongs to CHEM 210 at Pennsylvania State University taught by Maslak in Fall 2016. Since its upload, it has received 228 views. For similar materials see Organic Chemistry I in Chemistry at Pennsylvania State University.
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Date Created: 09/18/16
Chemistry 210 Chapter 2: Isomers and Stereochemistry Lectures 8,9, and 10 9/9/16-9/16/16 Lecture 8: Isomers, Hydrocarbon Nomenclature, and Definitions Nomenclature: Prefix-Locant-Parent-Suffix Prefix: where/what the substituents are Locant: where is the primary functional group Parent: how many carbons Suffix: what is the primary functional group -functional groups -groups of atoms whose structure/chemical behavior does not change substantially, regardless of environment -isomer -term that describes structural relationships between molecules that appear to be similar -have to be drawn and counted -some notation: 1- primary 2- secondary 3- tertiary 4- quaternary -indicates the number of carbons attached to a carbon -also applies to hydrogen -based on carbon they are attached to Definitions: -chiral molecule -any molecule that has a non-superimposable mirror image -achiral -not chiral -enantiomer -a pair of molecules that are non-superimposable mirror images of one another -racemic mixture -a 50/50 mix of enantiomers -optical activity -the physical property of rotation of plane-polarized light by a solution of chiral molecules -stereogenic center -an atom that has 4 different substituents -diastereomers -any stereoisomers that are not the same molecule or mirror images of one another -geometrical isomers -molecules that differ only by rotation about a double bond -enantiomeric excess -measured excess of one enantiomer over the other in a mixture of enantiomers Lecture 9: Enantiomers and Diastereomers -absolute configuration -molecular level structural characteristic -determining absolute configuration: -assign priority numbers -based on atomic number -isotopes with higher mass have priority -lone pair has lower priority than H -orient molecules with lowest priority pointing away -assign direction based on priority decrease -R for clockwise -dextrorotary -S for counterclockwise -levorotary -multiple bonded atoms are considered equivalent to the same number of single bonded atoms -use of dummy atoms -absolute configuration and the electrostatic charge of molecule are NOT the same -enantiomers have identical physical and chemical properties in achiral environments -except optical activity -diastereomers have different chemical and physical properties Chirality: -indications: -1 stereogenic center (4 different substituents) -more than 1 stereogenic center -counter indications -plane of symmetry -symmetry center (rare) -complications: -chiral compounds without stereogenic center (chiral shapes) -achiral compounds that have 2 or more stereogenic centers (meso) -compounds that have chiral shapes or centers but are not chiral -rapid process of interconverting the enantiomers -the following have meaning if on a stereogenic center: -lines = no stereochemistry implied -wedges = single enantiomer (triangle) -bars = racemic mixture (rectangles) -relative stereochemistry Lecture 10: Inversion, Geometrical Isomers, and Chirality in Nature -inversion of stereogenic centers: -involves atoms with lone pairs -enantiomers -inverts, intermediate configuration is planar -occurs because inversion doesn’t cost a lot of energy -planar intermediate = achiral = no optical activity -process occurs even more easily with radicals -hence the instability of radicals -molecules previously known as “cis” and “trans”: -high priority on same side = Z (cis) -high priority on opposite side = E (trans) -if enantiomers have the same chemical and physical properties then why did the samples passed around in class smell different? -enantiomers have the same properties in ACHIRAL environments -humans are chiral -our scent receptors are chiral -has an influence on what we smell