Notes for week 5
Notes for week 5 Chem 345
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This 2 page Class Notes was uploaded by Bethany Lawler on Friday September 25, 2015. The Class Notes belongs to Chem 345 at Washington State University taught by Dr. Crouch in Summer 2015. Since its upload, it has received 22 views. For similar materials see Organic Chemistry 1 in Chemistry at Washington State University.
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Date Created: 09/25/15
Chemistry 345 Week 5 921 925 1 Stereochemistry A chiral compound is optically active This means they rotate a plane polarized light When the light is rotated clockwise a is added to the notations When clockwise a There is no way to predict which direction a compound will rotate but a chiral molecule s enantiomer will always reverse the direction A mixture with equal parts of a chiral molecule and its enantiomer called a racemic mixture has no optical activity Fischer projections are a way of representing a chiral molecule The four substituents that are bonded to the carbon are aligned with the cardinal directions and drawn at The assumption is that the two substituents to the right and left or east and west if you like are coming out of the plane of the paper and the substituents to the north and south are below the plane of the paper When naming a chiral molecule the handedness of the molecule must be assigned This is determined in the following way 0 The substituents are assigned priority based on atomic number The largest atomic number has the highest priority If two substituents have a fist atom of the same atomic number the chain is traced to the next major atom in the chain and whichever is larger has more priority For example if two of the substituents are CH3 and CH2CH3 the CH2CH3 group will have higher priority because after the initial carbon which is the same as CH3 it has another carbon whereas CH3 only has a hydrogen 0 After priority has been assigned a Newman projection is created by eclipsing sighting along the bond the lowest priority substituent o The molecule is then rotated in such a way that the highest priority group goes towards the second highest priority group 0 If it goes in the clockwise direction the molecule is R o If it goes in the counterclockwise direction the molecule is S When the handedness is determined the chiral center is labeled R or S in front of the compound name in parentheses in the following manner of chiral center in chainRS of chiral center in chainRS In a compound with multiple stereo centers chiral atoms there will be 2n stereoisomers where n is the number of stereo centers The easiest way to predict the shape these isomers is to use a Fischer projection No matter the number of stereo centers each individual formation of the compound only has one enantiomer The other formations which are not enantiomers of the given formation are called diastereomers In cyclic compounds the entire ring must lack symmetry for a chiral center to exist These have cis and trans isomers as well as enantiomers 2 Alkenes Alkenes are unsaturated hydrocarbons they contain double bonds When naming them they use almost all of the same conventions as alkanes but there use the suffix ene and the locations of the double bonds are indicated before the suffix and the number of bonds is indicated using the naming prefixes just as for substituents The carbon chain for alkenes is numbered from the end closest to the double bond so that the double bond falls on the smallest number When a double bond acts as a substituent such that one of the carbons in the double bond is also bonded to a carbon in the main chain it is called vinyl When a double bond acts as a substituent and it is bonded to another carbon which is then bonded to the main chain it is called allylic Because double bonds do not rotate they have cis and trans isomers but cis and trans are only applicable labels when there are two hydrogens When there are not two hydrogens present EZ notation must be used EZ notation is applied in the following way 0 The substituents on the double bonded atoms are assigned priority in the same way that substituents on a chiral molecule are assigned 0 When the two highest priority molecules are on the same side this is known as Z 0 When the two highest priority are on opposite sides this is known as E Note when two isotopes of the same atom are substituents the heavier isotope has higher priority 3 Reactions An electrophile is a Lewis acid that has a positive or partial positive charge or and incomplete octet A nucleophile is a Lewis base that has a lone pair andor negative charge A carbocation is a carbon that is electrophilic Carbocations are classified as primary secondary or tertiary based on how many other carbons they are bonded to The more substituents a carbocation has the more stable it is because they substituents help balance the slightly positive charge
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