CH 221 Edition 7Exam # 2 Study Guide Lectures: 1 - 25Note: This exam is cumulative so be sure to study lectures 1-12 from the previous study guide as well.Lecture 13 (February 6th) Plane Polarized Light- A chiral compound is optically active and rotates the plane of polarization in polar-polarized light- If it rotates the plane clockwise, it is (+) Dextroratory- If it rotates the plane counterclockwise, it is (-) Levoratory-[α]λT= αlxc -α = observed optical rotation-c=¿ concentration of solution (g/ml)-l = length of tube in decimeters- Enantiomeric excess = observed specific rotationspecific rotation of pure enantiomerx 100 %Compounds with Two Asymmetric Centers- When both hydrogens are on the same side of the Fischer model, it is called erythro- When hydrogens are diagonal to each other on the Fischer model, it is called threo- Diastereomers are stereoisomers that are not enantiomersLecture 14 (February 11th) Two asymmetric centers in three stereoisomers includes a meso compound and a pair of enantiomersMeso compounds have a plane of symmetry and have superimposable mirror images.- Cis- a meso compound- Trans- pair of enantiomers- Rings can be trans-fused or cis-fusedStereocenter- an atom at which the interchange of two groups produces a stereoisomer- Cyclic structures restrict rotation- Cis- substituents on same side of ring- Trans- substituents on opposite sides of ringAlkenes have a molecular formula= CnH2 n+n - There are two hydrogens for every π bond or ring- Degree of unsaturation= total number of π bonds and rings- Saturated hydrocarbons have no double bonds- Unsaturated hydrocarbons have one or more double bonds- Replace “ane” of alkanes with “ene” to name alkenes- Functional group gets lowest possible numberLecture 15 (February 13th)Stereoisomers are named using cis or trans prefix- Two double bonds = dieneNumber in the direction so that the functional group gets the lowest number- Substituents are listed in alphabetical orderCycloalkenes- A number is not needed to denote the position of the functional group: it is always between C1 and C2Vinylic- the sp2 carbon of an alkene- Allylic – carbons adjacent to vinylic carbons- Double bonds have restricted rotation- Rotation around a double bond would break the π bond- Six atoms of an alkene are in the same planeZ = zusammen (together) E = entgege (opposite)- Relative priorities depend on atomic numbers of the atoms attached to the sp2Lecture 16 (February 16th)An electrophile has a positive charge, a partial positive charge, or an incomplete octetNucleophiles have a negative charge or lone pair- Curved arrows used to show mechanics of a reaction- Mechanism of a reaction is a step-by-step description of the process by which the reactants are converted into products- Y ↔ Z- Thermodynamics: how much Z is formed- Kinetics: how fast Z is formed- A reaction coordinate diagram shows the energy changes that take place in each step of a reactionEquilibrium Constant- gives concentration of reactants and products at equilibrium- m A + n B ↔ s C + t D- Keq = [products][reactants]- Keq = [C ]s[ D]t[ A ]m[ B]n- ∆Gº = -RT ln KeqGibb’s Free Energy (∆Gº) - ∆Gº = ∆Hº - T∆Sº- Free energy of products – free energy of reactants- ∆Hº = heat required to break bonds – heat released from bonds breaking- ∆Sº = freedom of motion of products – freedom of motion of reactantsRates of Reactions- Increasing concentrations increases rate- Increasing temperature increases rate- Rate can also be increased by a catalyst- Rate of reaction = (number of collisions per unit of time) x (fraction with sufficient energy) x (fraction with proper orientation)- A  B (first order reaction) rate = k[A]- K is the rate constant and rate is the rate of the reaction- A + B  C + D (second order reaction) rate = k[A][B]- K is the rate constant and rate is the rate of the reactionLecture 17 (February 18th)- The rate limiting step of the reaction is the step that has its transition state at the highest point of the reaction coordinate diagram - A catalyst provides a pathway for a reaction with a lower energy barrier- A catalyst does not change the energy of the starting point (the reactants) or the energy of the end point (the products)Carbocation Stability- Alkyl groups decrease the concentration of positive charge on the carbon- Hyperconjugation stabilizes a carbocation- The more stable carbocation is formed more rapidlyLecture 18 (February 20th)Carbocation rearrangement is a 1,2-hydride shif- A carbocation will rearrange if it can form a more stable carbocationHydroboration-Oxidation- Borane (BH3) is an electrophile- Electrophile is added to the sp2 carbon bonded to the most hydrogen- Reagents are numbered because the second set of reagents is not added until the first reaction is over- No carbocation rearrangement can be made for vicinal dihalides- Alkenes cannot add I2 because it makes it unstableAn oxygen-oxygen single bond is a very weak bondLecture 19 (February 23rd)The formation of an epoxide converts a peroxyacid into an epoxide- MCPBA is a commonly used peroxyacidOzonolysis- Double bond is broken, bond is replaced by two double bonded oxygens-O3 is ozone- Ozone  molozonide  ozonide- Ozonide is converted to ketone and/or aldehyde. The addition of hydrogen requires a catalyst Pd/C- Catalytic hydrogenation is a reduction reactiona. Stabilities of AlkenesMost stable 4 R groups> 3 R groups> 2 R groups> 1 R groups> least stableTrans is more stable than Cis because the Cis isomer has a steric strainRegioselective reaction = A  B + C (B and C are constitutional isomers) more B is formed than C- Stereoselective reactions = A  B + C (more B is formed than C)- Stereospecific reaction A  B, C  D, all being stereoisomersLecture 20 (February 25th)- When a reactant that has an asymmetric center forms a product that has a new asymmetric center, that product is a pair of diastereomers- Four stereoisomers are obtained if the reaction forms a carbocation intermediate- A pair of enantiomers result from syn addition- The addition of H2 is considered a syn addition- Syn addition to a Cis isomer forms only the erythro stereoisomers- If the substituents are the same, the erythro stereoisomer is a Meso compound- Syn addition of H2 to a trans isomer forms only the threo stereoisomer- If the substituents are the same, the Cis stereoisomer is a Meso compound- Cyclic alkenes are Cis unless they have at least eight ring