CHM 255 Exam 2
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| Define chiral | An object is not super imposable on its mirror image
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| What constitutes a stereocenter | A carbon with 4 different groups attached to it
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| What are enantiomers | Non-super imposable mirror images with one chiral center
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| How do you determine between pairs of enantiomers in nomenclature | R (clockwise) & S (counterclockwise)
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| What is the purpose of the Cahn/Inglod/Prelog rules? | Indicate the chirality or handedness of a stereocenter
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| How to determine R or S enantiomerism (3 steps) | 1. Order substituents by atomic weight of the 1st atom attached to the sterocenter
2. Put the lowest order substituent away from you
3. Draw an arrow connecting substituents 1,2,3: clockwise(R) & counterclockwise (S)
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| Where do you put the R/S in nomenclature? | At the very beginning of the name
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| What do you do if the 1st atoms attached to the stereocenter are the same? | Go to the next attached atoms and the one with the highest atomic weight wins
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| How do you determine R/ S priority with double/triple bonds | Double-Count as an extra carbon atom on each carbon in the double bond
Triple - count as 2 extra carbon atoms on each carbon in the triple bond
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| If one enantiomer is in an R arrangement can you determine the other? | Yes; S
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| How do you determine R/S if H is in the plane of the paper? | Put your eye on the other side of the molecule and use the reversal rule
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| What are fischer projections good for | Acyclic molecules with more than one chiral center
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| What do the vertical and horizontal lines in a fischer projection represent? | Vertical: bonds going into the plane
Horizontal: bonds coming out of the plane
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| When checking to see if molecules are superimposable you should rotate the fischer projection ____degrees ___the plane of the paper. | 180; INTO
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| For an acyclic molecules with n stereocenters, what is the maximum number of steroisomers possible? | 2^n
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| What are diastereomers | Stereoisomers that are not mirror images
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| What is a meso compound | An achiral molecule having 2 or more stereocenters
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| What are the 3 properties of enantiomer pairs | 1. Identical physical properties
2. Interact with and rotate plane polarized light
3. May interact with biological systems differently
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| _____________ molecules do not rotate plane-polarized light; __________ molecules do. | Achiral; chiral
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| Rotation of plane polarized light to the left is (?), right is (?) | (-); (+)
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| Enantiomers rotate plane polarized light how much and in what relative direction? | The same amount; opposite directions
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| What is a racemic mixture | 1:1 mixture (equimolar) of a pair of enantiomers
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| Is a racemic mixture optically active and what is its specific rotation | Optically inactive; [a]^20D=0 deg
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| Optical Purity | Enantiomeric excess
=ee=([a]Dimpure/[a]Dpure)*100
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| What are 3 characteristics of diastereomers | 1. Unique molecules with unique physical properties
2. Interact with plane polarized light differently
3. May interact with biological targets differently
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| What is an alkene? | Organic molecule that contains a double bond
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| ____ alkenes are less stable because of ______. | cis; strain in the interaction between CH3 groups
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| 3 Rules for nomenclature of alkenes | 1. Use the infix -en instead of -an
2. The parent chain is the longest containing the double bond
3. # the parent chain so that the double bond has the lowest # possible
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| How to use the E-Z system (3 steps) | 1. Use R-S priority rules
2. Divide molecules in two and compare priority of 2 substituents on each side
3. Z: high/high or low/low; E: high/low or low/high
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| Bond length: 1. Alkane 2. Alkene | 1. 1.54 A
2. 1.34 A
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| Bond dissociation energy: 1. Alkane 2. Alkene | 1. 90kcal/mol
2. 172 kcal/mol
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| Bond rotational barrier: 1. Alkane 2. Alkene | 1. Relatively free rotation around C-C (3kcal/mol)
2. p-orbitals& pi bond restrict rotation (63kcal/mol)
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| Many organic reactions have an energy of activation of _________________? | 10-35 kcal/mol
10-20 can happen at room temp
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| What kinds of molecules are nucleophiles (3)? | 1. Compounds with a site of (-) charge
2. Compounds with atoms with love pairs of electrons
3. Compounds with pi bonds
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| What kinds of molecules are electrophiles (2)? | 1. Compounds with a site of positive charge
2. Compounds that have an electron deficient site
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| Nucleophile vs electrophiles | Nucleophiles: donate e-; electrophiles: accept e-
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| A bond in the _________ may need to break in order to maintain the octet rule | electrophile
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| Alkenes will be a _____________ that can be treated with many different ________ | nucleophile; electrophiles
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| What is electrophilic addition | Adding an electrophyle to an alkene
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| What is a carbocation? | A cation of carbon
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| What is the order of carbocation stability? | methy cation < 1(o) < 2(o) < 3(o)
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| In what two ways can alkyl groups stabilize carbocations | 1. inductive effect: neighboring carbons help share the positive charge (donate e- density)
2. hyperconjugation: adjacent pi bonds overlap with the vacant p orbital
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| Why would a rearrangement occur | Hydrogen can shift to form the more stable carbocation
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| T/F: Alkyl groups and hydrogens can shift to any carbon on the molecule to form the most stable carbocation | FALSE: Can only shift to the C next door
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| What does it mean to be stereoselective? | One stereoisomer is formed in preference to all others; occurs for reactions with a bridged ion intermediate
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| What is anti-addition? | Addition from opposite sides of the double bond
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| Cyclic addition of alkenes always yields a molecule that is a. cis, b.trans, c. both, d. neither | b. Trans
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| Markovnikov vs. Anti-Markovnikov addition | M: Substituent ends up on the more substituted end of the double bond
A-M: Substituent ends up on the lest substituted
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| What are conjugated double bonds | When two or more double bonds are separated by one single bond
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| What are unconjugated double bonds | When two or more double bonds are separated by more than one single bond
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| Which is more stable and why between a conjugated and unconjugated double bond? | Conjugated because e- in the pi system can be delocalized over both double bonds
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| A reaction is an oxidation if the starting material 1.___OR 2.___. | 1. Has lost H2
2. Has gained O
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| A reaction is an reduction if the starting material 1.___OR 2.___. | 1. Has gained H2
2. Has lost O
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| What is syn addition | Stereoselectivity: Addition of H2 on the same side of the double bond; results in a cis product
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| How do you form a radical | Homolytic cleavage: Take a bond with 2e- and send on in each direction
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| How do you indicate that you are moving only 1 e-? | 1/2 an arrow head
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| A reaction of radicals will proceed until all radicals are consumed. A process known as _______________ | Chain termination
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| What is the result of non-productive chain termination when forming alkyl halides from alkanes | The reactant or the reagent reforming
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| What is the relative stability of allylic radicals? | Allylic radicals>3(o)>2(o)>1(o)
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| When is electrophillic addition possible | ONLY at room temperature
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| How can we avoid the problem of unwanted electrophilic addition reaction at room temp with alkenes and Br | Using a different reagent: NBS
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| What does halogenation of alkanes | Heat/Light and Cl2 or Br2 or NBS
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| What is an allylic carbon | Adjacent C to a C=C... C1-C2=C3 & C1 is allylic
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| What is allylic substitution | A substitution a the allylic C
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