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Exam 2: CHEM245 Study Guide

by: Brie

Exam 2: CHEM245 Study Guide Chem 245-002

Marketplace > Colorado State University > Chemistry > Chem 245-002 > Exam 2 CHEM245 Study Guide

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This study guide thoroughly covers chapters 4, 5, and 6. Included are examples and drawings further explaining the concepts. I've included 50 practice problems with an answer page. Good Luck! ...
Fundamentals of Organic Chemistry
Patricia Somers
Study Guide
Organic Chemistry, chem245, Ochem, coloradostate, csu, exam2, ochemexam2
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This 16 page Study Guide was uploaded by Brie on Monday October 10, 2016. The Study Guide belongs to Chem 245-002 at Colorado State University taught by Patricia Somers in Spring 2015. Since its upload, it has received 58 views. For similar materials see Fundamentals of Organic Chemistry in Chemistry at Colorado State University.


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Date Created: 10/10/16
Study Guide: Exam 2    CHEM245 Chapter 4  1  E/Z Isomers  o E Isomer: Two groups with the higher priorities are on opposite sides o Z Isomer: Two groups with the higher priorities are on the same side 2) Identifying asymmetric centers  o Stereocenter: Bonded to 4 groups  1. Don’t include atoms that can’t be chiral centers  a. CH2 (due to hydrogens attached), CH3 (due to hydrogens  attached), NH2 groups, Oxygens, Halogens, atoms that are  a part of double or triple bonds (double and triple bonds can’t have bonds to four different groups)  2. Check for an atom with 4 groups attached to it 3   Chiral v. Achiral and Mesocompounds   Chiral: No mirror image o Ex) Hands or Keys o Has stereogenic center o Chiral molecule is optically active  Achiral: Mirror Image o Doesn’t have a stereogenic center o Ex) A Baseball  Meso Compound: Has multiple stereocenters that are superimposable on  it’s mirror image  o Must have 2 stereocenters 4   Determining if an asymmetric center has the R or S configuration  R Configuration: If priority groups go clockwise around the stereocenter  S Configuration: If priority groups go counterclockwise around the  stereocenter 5   Identical, constitutional isomers, enantiomers, diastereomers, geometric  isomers or unrelated).   Constitutional Isomers: Same molecular formula and different connectivity/ arrangement   Enantiomers: Non­superimposable mirror images and contain chiral  centers o Chiral  Disastereomers: Stereoisomers that are not mirror images of each other  but contain chiral centers o Different chemical and physical properties   Geometric Isomers: Cis/ Trans or E/Z  Identical Molecules: Superimposable mirror images that are achiral   Unrelated: If the chemical formula is not identical then they are not  isomers  Chapter 5    1)  Electrophile vs. Nucleophile.   Electrophile: Region of low electron density (+)  o Electron Lover   Nucleophile: Higher electron density (­)  o Nucleus Lover o Lone pairs/ Negative Charge/ Double Bonds aka electrons to share  Electrons flow from high electron density to low electron density   Negative attracted to positive  2)  Draw products or intermediates from curved arrows on reactants or  intermediates.   Curved arrow: Shows where the electrons start from and where they’ll go  to  o Tail = origin o Head = destination  o Never goes from positive to negative charge  o If arrow starts at bond between two atoms, then that bond is  broken  o If the arrow ends between 2 atoms then a new bond is formed  there (If atoms are already bonded then that indicates a double or  triple bond)  o Charges  Decreasing Charge: Atom shares a lone pair (which it  previously had) so it’s /charge decreases by 1; neutral  would be +1  Increasing Charge: Atom gains a bonding pair all to itself,  then the charge will increase by 1; neutral would be ­1 3) Drawing the correct curved arrows given reactants and/or intermediates  and/or products.  4)   Stereoselectivity.   Stereoselectivity: Property of a chemical reaction where a single reactant  forms an unequal mix of stereoisomers. 5) Reaction coordinate diagrams, qualitative relationships between G and  Keq, energy of activation, the rate of a reaction.   Reaction Coordinate Diagrams o Describes energy changes in a reaction  o Total Energy of species v. progress of reaction o Left (reactant) to Right (product)  o Stability: The more stable a species, the lower the energy  o Transition State: The reaction maximum energy state   If transition state is too high in energy then the reaction will  not take place o Equilibrium Constant: A relationship based on equilibrium  concentrations o Favorable Reaction: Reasonable likelihood to proceed if favorable  o Gibbs Free­Energy Change: A thermodynamic quantity = to  enthalpy minus the product of entropy   Free energy of products – free energy of reactants   If products are more stable: o Δ G is negative o Reaction releases more energy than it consumes o Exergonic  If products are less stable: o ΔG is positive o Reaction consumes more energy than it releases o Endergonic o Exergonic: Releases energy o Endergonic: Consumes energy  Always requires energy to start   Keq o What happens to Keq if products are favored?  It will be greater than 1 o What happens to Keq if reactants are favored?  It will be less than 1   G vs. Keq Relationship o If Keq is greater than 1 then Δ G ° is negative (Exergonic) o If Keq is less than 1 then Δ G ° is positive (Endergonic)   Energy of Activation:   Rate of reaction: Rate = change in concentration/ change in time  6) The rate limiting step given a reaction coordinate diagram     Rate determining step (or Rate Limiting Step): The step that has it’s  transition state at the highest point on reaction coordinate diagram  7) Rate Constant   A fast reaction will have a large rate constant  A slow reaction will have a small rate constant  8) The effect of a catalyst on a reaction    Increases the reaction rate by lowering the activation energy of the  reaction  Catalyst is not consumed or changed during a reaction  With catalyst present, the sigma H2 bond breaks and the two hydrogen  atoms will bind to the metal With metal interaction, the pi bond of the alkene weakens  9) Heats of hydrogenation to rank relative stability.     Least stable = Least substituted   Most stable = Most substituted  Chapter 6    1) Naming an alkene, cycloalkene or an alkyne.   Alkene: One or more double bonds o Changes from “ane” to “ene’  o The number will indicate where the double bond is o Naming starts with the part closest to the double bond  o Multiple Double Bonds:   “Diene”, “triene,” “tetraene” etc.  Vinylic Carbon: The sp2 carbon of an alkene   Allylic Carbon: The sp3 carbon adjacent to a vinylic carbon  Vinylic Hydrogen: The hydrogen bonded to a vinylic carbon  Allylic Hydrogen: The hydrogen bonded to an allylic carbon  Cycloalkene: Closed ring of carbon atoms   Alkyne: An organic chemical compound that contains a triple bond  o Naming: “ane” to “­yne” o Terminal Alkyne: A triple bond at the end of a chain  o Internal Alkyne: A triple bond located elsewhere on the chain 2  Regioselectivity. Know the reagents needed to do the reaction, if given the  reactant and product.   Regioselective: A reaction in which 2 or more cnsitutional isomers could  be obtained as products but one of them predominates  o H will add to the carbon with the most H o The halide will add to the carbon with the least H 3) Relative stability of carbocations.   Resonance: A stabilizing feature  o How? It delocalizes the positive charge and creates more bonding  between adjacent atoms  o Decrease electron deficiency = Increases the stability   Increasing substitution increases stability   Resonance is more important than substitution  i. Ex: A secondary carbocation without resonance would be  considered less stable than a primary carbocation with resonance


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